State of MN GPS Base Station Task Force, Update of MN, Sept 1994
Click HERE for graphic.
TABLE OF CONTENTS
TASK FORCE MEMBERSHIP. . . . . . . . . . . . . . . . . . . . . . . 2
EXECUTIVE SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . 3
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
TASK FORCE PURPOSE . . . . . . . . . . . . . . . . . . . . .11
PILOT PROJECT
TASK FORCE VISION . . . . . . . . . . . . . . . . . . . . . .11
TASK FORCE- CONCEPT . . . . . . . . . . . . . . . . . . . . .12
USERS NEEDS FOR GPS . . . . . . . . . . . . . . . . . . . . .12
CURRENT & FUTURE USES FOR GPS . . . . . . . . . . . . . . . .15
VISION FOR FUTURE USES OF GPS BY STATE OF MN. . . . . . . . .17
PLAN, STRATEGY, & STAGING . . . . . . . . . . . . . . . . . .17
COSTS . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
OUTCOMES . . . . . . . . . . . . . . . . . . . . . . . . . .20
PROBLEMS NEEDING DECISIONS. . . . . . . . . . . . . . . . . .21
CONCLUSIONS
ITEMS LEARNED FROM PILOT PROJECT. . . . . . . . . . . . . . .26
RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . .29
GLOSSARY . . . . . . . . . . . . . . . . . . . . . . . . . . . i-xix
APPENDICES
A. CURRENT GPS APPLICATIONS IN MN STATE & FED GOVERNMENT
B. ANTICIPATED GPS APPLICATIONS IN MN STATE & FED GOVERNMENT
C. EXISTING GPS EQUIPMENT IN MN STATE & FED GOVERNMENT
D. DIAGRAMS AND A LIST OF GPS BASE STATION LOCATIONS
E. OBTAINING GPS DIFFERENTIAL DATA IN MN
F. PCA POSSIBLE NOMINAL ACCURACY STANDARDS
TASK FORCE MEMBERSHIP
Minnesota Department of Transportation
Dave Gorg, Surveying & Mapping Section, (612) 296-5710
W. Todd Smith, Office of Information Policy, (612) 296-3741
Keith Slater, Metro Division Surveys, (612) 593-8464
Bob Fritz, Metro Division Surveys, (612) 797-3106
Andy Terry, Office of Electronic Communications, (612) 296-
7421
King Fung, Office of Electronic Communications, (612) 297-8266
Minnesota Department of Health
Justin Blum, Environmental Health Division, (612) 627-5165
Minnesota Pollution Control Agency
Yuan-Ming Hsu, Groundwater & Solid Waste Division, (612) 297-
2716
Minnesota Department of Natural Resources
Judy Winiecki, Bureau of Engineering, (612) 296-3589
University of Minnesota
Will Craig, Center for Urban & Regional Affairs, and Minnesota
Governor's Council on Geographic Information, (612) 625-1551
United States Army Corps of Engineers
Terry Birkenstock, GIS Center, (612) 220-0271
United States Department of Commerce, NOAA
Dixon Hoyle, National Geodetic Survey Division, (612) 296-1542
Metropolitan Airports Commission
Roy Fuhrmann, Aviation Noise/GIS Specialist, (612) 725-8334
2
EXECUTIVE SUMMARY
The Global Positioning System (GPS) first proved itself openly
to the world in Desert Storm. By using satellites for navigation
and inventory location methods, people could navigate effectively
in the middle of a desert at night, fly to targets of which they
had no maps, and program weapons to arrive at a specific window
miles away. The capability of GPS is tested and proven. Now, the
civilian community can save time and expense by using this
locational capability for an unlimited number of civilian
applications.
GPS is an essential part of almost all Geographic Information
System activities. Since we need to know where items occur, how to
get back to known places, and associate resources with other
resources, GPS provides us with the location coordinates we need.
Many different levels of appropriate accuracy (ñ 100 meters to ñ
1cm) can be obtained with various GPS equipment 24 hours a day,
anywhere on the earth. The simplicity and promptness of obtaining
this locational information by electronically attaching real-world
coordinates to any other data gathered make it an obviously
essential part of the day-to-day operations of anyone engaged in
resource management, facilities management, navigation, surveying,
transportation, and construction. Currently, there are boats,
trains, automobiles, airplanes, and pedestrians using GPS to
navigate, inventory, and track equipment, natural resources, and
personnel. This report is a first attempt to coordinate the GPS
knowledge, experiences, and directions for Minnesota State
Agencies. As this task force met and the pilot project unfolded,
it became apparent that we were on the leading edge of
coordination, development, and use. Other agencies, states,
counties, and private interests were kept informed, and were eager
to coordinate their work. ' Private vendors were asked to work
together to create the desired capabilities.
The "raw" GPS signal gives only ñ 100 meter accuracy. With
additional processing, using Differential GPS (DGPS), one can
improve the accuracy. The INTRODUCTION of this report explains DGPS
further. Users need Real Time Correction Messages (RTCM) which
corrects "raw" GPS signals immediately in the field instead of
hours or days later. RTCM makes DGPS viable for many more
applications.
3
Below is a summary of the factors and decisions leading to this
pilot project.
. GPS was endorsed as the location method of choice by both the US
Secretary of Transportation, and by the Intelligent Vehicle Highway
Society of America (IVHS America) this summer.
. The U.S. EPA identified GPS as the principal location method for
meeting their location data policy.
. GPS is an essential part of Automatic Vehicle Location (AVL),
Geographic Information Systems (GIS), IVHS, surveying, resource
management, and facilities management.
. making DGPS RTCM widely available in this pilot project's non-
proprietary method has not been accomplished before.
. because of the incredible opportunity to share resources (human &
equipment) in the learning, standards setting, automation, and
using of GPS equipment, it is imperative that state and local
government agencies coordinate their efforts.
. The DOT took the lead on this effort because:
. the DOT had many functional units looking at using GPS for
feature/incident location, surveying, facilities management,
and vehicle tracking & navigation.
. the DOT has the Office of Electronic Communications which handles
the electronic communications (radio repair & installation,
computer repair, etc.) for all MN state agencies.
. the DOT has a Geodetic Unit which maintains a geodetic
control monument database and was experienced with GPS
equipment since a 1985 cooperative effort with Ramsey County
to obtain a high-accuracy geodetic network for the Metro area.
. the Mn/DOT Geodetic Unit houses a National Geodetic
Advisor(US Department of Commerce, NOAA) who is an invaluable
resource about GPS data types and capabilities.
. the RTCM pilot project will mount a radio broadcast antenna on
the top of the First Bank Building in downtown Minneapolis.
. the radio frequency (151.445 mhz) will need to be received by
radio equipment and processed for use by non-proprietary GPS
receivers. Motorola has agreed to work on interfacing Motorola
radios to both Trimble and Magellan GPS receivers.
. even if the military didn't degrade (Selective Availability = SA)
the GPS signal, this RTCM would still be necessary to obtain better
accuracy than the "degraded" GPS signal. These other errors are
due to local atmospheric distortion.
4
. for this pilot project, many agencies supplied personnel, one state
agency supplied a dedicated statewide radio frequency, another agency
supplied the GPS base station and a dedicated phone line, and a third
agency bought the needed antenna and other radio equipment.
. if not for this coordinated and publicized effort, two or three
agencies and at least one county would have each sent $60,000+ for
redundant efforts. Instead, that cost was shared by each of the
agencies, and further cooperative funding agreements will be pursued.
. standardization of equipment is needed and being pursued to simplify
purchasing, resource sharing, and support.
. we considered all of the known alternative technologies and vendor's
methods of this data communication. Each method was either much too
expensive, did not have the wide area coverage, or was too
proprietary. We are still watching the rest of the world for
alternatives.
. this pilot project will teach many people a lot about the uses of
GPS, and help GPS fulfill its label as the "next utility". Regardless
of long-term decisions on RTCM broadcast methods, this learning and
education is still necessary.
RECOMMENDATIONS
. Get GPS equipment on "state contract" or allow purchasing
from Government Service Agreement (GSA).
. Decide who will be long-term equipment maintenance agency(s).
. Transfer of MDH GPS base station to another agency (Mn/DOT?).
. Concentrate efforts on providing sub-meter accuracy, code-
phase (< 1 m), real-time corrections for underground utility
location and other infrastructure applications.
. Monitor the development of FM side-band technology (RDBS) vs
a dedicated radio frequency that was used for the pilot
project. Current incompatibilities need to be resolved.
. Keep track of satellite broadcast technology for real-time
DGPS.
5
. Where possible, use a submeter base station since it will also
serve the ó5 m users and costs about the same.
. Keep track of FAA's activities. They may have statewide ó6 m
available for at least aircraft in 1995-96. We may be able to
rebroadcast their signal for ground/land use.
. Continue this task force with a new charge something like
... Study options and recommend the most economical and
practical solution to providing real-time DGPS statewide
Identify costs for testing the plan once plan is developed.
Develop and conduct joint projects (partnerships). Have this
task force report about current issuers and trends every six
months to the Governor's Council on Geographic Information.
. Provide the above task force formal involvement with all
initiatives where GPS technology will be used.
. Seek to develop agreements with county and municipal
governments to share the cost and development of running base
stations or ask the legislature to consider base station
operations as a line item, defining the agency responsible
for the administration.
. Seek to increase all agencies' funding of DOT's Office of
Electronic Communications to cover the costs of operating base
stations statewide.
. Create a policy that states any agency creating a new DGPS
base station will make the data files available via Internet
until real-time is available statewide. The central
coordination for these data files could be through the
Minnesota Land Management Information Center (LMIC).
. Focus on getting real-time DGPS available in population
centers (Metro, Duluth, Rochester, Brainerd/St. Cloud) over
the next two to three years. As submeter real-time DGPS
becomes available nationally (such as through the FAA) and
technology improves, convert the former stations to use for
centimeter accuracy work -- maybe as roving stations for
project/area specific work.
6
. Try to find an additional statewide frequency for use by the
roving real-time DGPS base stations.
. Continue to track DGPS private service providers' DGPS
positional accuracy and costs. Currently, costs are much too
high to warrant state agencies (with 1000's of users) using
them (see Table 1 below).
Table 1
State/Public Private
Service Service
Initial Equipment Costs $6,000 $6,000
Annual equipment rent
x 5000 (minimum users) 0 $10-20.0M
Annual equipment
maintenence, operating base $1.0M 0
station, staff, & utility fees
x20 (maximum stations)
TOTAL ANNUAL COSTS $1.0M $10-20.0M
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NTRODUCTION
The Global Positioning System (GPS) is a precise location and
navigation information technology that uses orbiting satellites
developed by the US Department of Defense for military
applications. GPS technology employs a constellation of 24 NAVSTAR
satellites orbiting the Earth twice a day. These satellites
orbiting the Earth twice a day. These satellites transmit highly
precise timing data generated by on-board atomic clocks. A GPS
receiver on the Earth picks up this timing information along with
satellite location information from at least four of the satellites
and mathematically computes latitude, longitude, altitude and clock
synchronization information.
The applications of GPS technology are endless- From
positioning soil drilling rigs to landing aircraft in low
visibility, from mapping highway facilities to management of snow
plows and emergency vehicles. For most of these applications
Differential GPS (DGPS)- a more accurate form of GPS information-
is needed (see Figure 1).
Click HERE for graphic.
8
GPS is an advance form of GPS that improves the accuracy of the
system from 100 meters of error (obtained with single receiver and
no differential corrections) to 1-5 meters of error for the less
costly receivers, and sub-meter or even centimeter accuracy for
more expensive receivers.
To understand how differential GPS works, we first need to
understand how those 100 meters of error creep into standard GPS
measurements. A variety of factors, both natural and man-made, are
to blame. One of the biggest culprits is the Earth's atmosphere.
Since the speed of light depends on the medium though which it
travels, GPS signals can be delayed as they move through variations
in the ionosphere and troposphere. This delay causes a
miscalculation of distance which, in turn causes errors in
position.
Click HERE for graphic.
9
nother source of error is the satellites themselves. Even though
they're synchronized by high-accuracy atomic clocks, these clocks are
still subject to slight inaccuracies which lead to position errors.
Furthermore, as the satellites drift from their predicted orbits,
further distance calculation errors can mount up.
On top of that, the Department of Defense reserves the right to
intentionally degrade the accuracy of the GPS signal for strategic
purposes. This policy called "Selective Availability" is the largest
source of the 100 meters of error to the equation.
Fortunately, DGPS counteracts all of these sources of error,
tightening up the working accuracy of GPS to just a few meters (even
better if you're stationary).
The technique is based on putting an extra GPS receiver at a known
locations location that has been independently surveyed to very high
accuracy. As GPS signals are received at this "reference station,"
the receiver calculates distances to the satellites based on the
satellites' GPS information and then compares it with its known
distances. Any difference between the two distances is a result of
the combined error sources mentioned earlier.
These errors in distance, or "error correction factors," can then be
applied to the readings of any mobile GPS receiver in the area. The
system works because the GPS satellites are so far out in space that
all receivers in the same local area on Earth receive signals that
passed through virtually the same slice of atmosphere and so have the
same errors.
The principle is simple, but getting it right under all conditions,
in real time, and without interruption, requires a sophisticated
integration of GPS hardware, software and communications technologies.
The charge of the GPS Base Station Task Force is to pilot differential
GPS services in a user friendly environment for the many applications
in state and local government. Since the State of Minnesota is
represented on the State of Wisconsin's GPS Task Force, and Wisconsin
was concentrating on post-processing of differential corrections, we
decided to concentrate our efforts on real-time differential
corrections, Both states were in contact regularly to share data and
to have input into the other's efforts.
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ASK FORCE PURPOSE
This task force purpose is derived from the original Statement of
Purpose & Charge from Mn/DOT's Council for Geographic Information.
. to coordinate access to GPS differential correction post-processing
base station files and broadcasting Real Time Correction Message
(RTCM) by Minnesota State Agencies
. to communicate and work with as many other public and private
partners as possible in sharing resources and developing standards
. to implement at least one GPS base station that governmental units
can access via computer network for post-processing of resource grade
(ñ 1-5 meter) differential corrections
. to conduct a pilot project to research test RTCM for use by many
state agencies
. to identify and evaluate the issues associated with the development
of a plan for carrier phase (ñ 1 meter) RTCM statewide
. to make recommendations for RTCM available statewide for code-phase
(ñ 1-5 m accuracy).
TASK FORCE VISION
It is the vision of this committee to implement a method of
determining geographic location that is economical, fast, accurate to
within one meter, and available statewide. As easy as looking at your
watch, this system can be used in real-time: no additional
computations or post processing of data. This location reference
system will be used to locate and relate all geographic information
in Minnesota for the purposes of resource management, facilities
management, decision making, planning, IVHS, etc.
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TASK FORCE CONCEPT
The concept that can best be used to achieve this vision involves
broadcasting a radio signal. This signal carries information for the
real time differential correction of positional information obtained
from GPS satellites. The corrections being broadcast are values
representing distance differences between true values and apparent
values observed at a predetermined time. The time of observation is
coordinated between the base station operator and a roving receiver
operator. The apparent value received at the roving receiver is
corrected by the difference computed at the base station.
This correction factor provides users in the field, who have
compatible GPS radio equipment, with the ability to achieve one meter
accuracy any place within the broadcast range.
The correction signal is to be broadcast over a State radio frequency
which covers most of Minnesota. The DOT Office of Electronic
Communications provides all state agencies with radio support and has
the technical expertise to provide this service. With statewide
coverage, all public agencies will be able to use differential GPS in
real-time. This will save money for all users, and provide uniformity
and standardization throughout the state.
The project is to be staged in three phases with a pilot project in
the metro area first. One future stage will provide statewide 1-5
meter accuracy, and another stage will provide sub-meter accuracy.
USER NEEDS FOR GPS
An assessment of the type and quality of locations needed is critical
for this project because it determines how the RTCM service is to be
delivered and whom it serves. User needs are broadly defined by
accuracy needs; in other words, the type and quality of locational
data needed is determined by the particular data use of the data or
problem to be solved.
There are many current uses for GPS technology in the public sector
and an unforeseeable number of future applications. These uses can
be classified into two general types: positioning and navigation. The
number of uses and users has
12
greatly increased in the past two years. The increase in demand is
exponential, not linear.
Positioning applications use GPS to create inventories of
geographically referenced features or objects, usually for further
analysis in a GIS. The end product of a positioning application is
not necessarily a physical map but could be the 'virtual" map created
in the computer. This electronic map is the foundation for navigation
applications.
Navigation applications use previously created inventories or maps to
locate, avoid, or navigate back to a feature or object. Potential
users of navigational GPS include all levels of government, public
utilities, and educational institutions that use geographically
referenced data, maps, and/or travel.
The following are grades of GPS accuracy in general use and the type
of institutional support needed for the particular accuracy:
Autonomous The GPS user that only needs location accuracies to
100 m does not need to perform differential
corrections and has no need for the RTCM broadcast.
This is generally called autonomous quality GPS.
The autonomous user needs the least amount of support.
Post-
Processing An application that requires accuracies smaller than
100 m, but not in real time, can obtain base station
data "after the fact" to perform differential
corrections. This is called post processing and gives
accuracies to 5 m or smaller but can not be used to
navigate because the accuracies are not available in
the field.
Post-processing requires minimal support because the
need for base station data is not time sensitive.
Data access is most efficiently provided via computer
network, less so over telephone modem, and least
effectively by hand transport of floppy disks by mail.
13
Navigation he applications that need the RTCM are those that
require better than 100 meter accuracy in real time.
Navigation application such as IVHS are generally of
this type and realtime 5 m accuracy measurements are
called navigation quality. Navigation requires the
most amount of support because of the radio link from
the base station to the roving receiver.
Survey Higher accuracy (1 meter or smaller) GPS measurements
are made by research scientists and land surveyors.
They perform what is generally called survey quality
RTPS.
The type of support needed for survey quality RTCM is
no different than navigation quality. However, the
number of base stations needed is greater because
accuracy is a function of distance from the base
station. It has been estimated that survey quality
RTCM will require a minimum of eight GPS base stations
located around the state. Whereas, statewide
navigation quality data can be obtained from the
existing base station.
The survey quality RTCM broadcast formats have not yet been
standardized by the responsible federal committees. Therefore, this
project is necessarily limited to implementing navigation quality
RTCM. As the high accuracy standard is defined, the ability to obtain
real time survey quality positions is planned to be included in the
statewide RTCM radio broadcast system.
There is a general consensus that IVHS will be the largest application
of GPS technology in the near future and, in particular, the largest
application of navigation quality GPS. Therefore, the current project
implementing RTCM broadcast in the Metropolitan Area is the most
appropriate to use as a pilot project because of the IVHS need for
navigation quality locations.
One side note. A common misunderstanding of GPS is the horizontal
coordinate system GPS uses, and the vertical elevation GPS gives. The
following page (Figure 3) gives a basic picture of the different
coordinate systems and the vertical measurement given by GPS.
14
Click HERE for graphic.
URRENT & FUTURE USES OF GPS IN
THE PUBLIC SECTOR
Applications that require navigation accuracies are found in many
state and local government agencies. When trying to describe the
potential user community for this type of service, it is often easier
to look at the function or kind of application rather than the agency
or program. The user community for the navigation quality GPS will
be drawn from agencies responsible for the following governmental
functions:
. Construction
. Facility, Traffic and Fleet Management
. Planning and Project Development
. Resource Management
. Public Health
. Public Safety
. Environmental Assessment
. Research
However, particular applications often overlap categories. For
instance, one GPS vendor has created a turnkey RTCM dispatch system
that tracks ambulance locations in a metropolitan area along with
traffic flow data. This system permits more intelligent decisions to
be made about routing of the ambulances and other emergency response
vehicles. The Traffic and Fleet Management, Public Safety, and Public
Health functions included in this application can also cross various
levels of government; local, state and federal.
In Minnesota, the public entities that currently use GPS (as of 7-20-
93) and the application or program area are listed on the next page.
15
Organization Division or Application
Counties; Dakota, St. Louis, Land Surveyors, GIS/LIS
and Itasca
State of Minnesota;
Dept. of Health Environmental Health
Dept. of Natural Resources Minerals
Dept. of Transportation Land Surveyors, GIS/LIS
Minnesota Geological Survey Water Well Inventory
Pollution Control Agency Ground Water and Solid Waste
Federal Government;
Fish and Wildlife Environmental Assessment
Army Corps of Engineers Construction Coast Guard
Navigation
NOAA Coast and Geodetic Survey
University of Minnesota;
Soil Science Dept., St.Paul Research
NRRI, Duluth Research
State Universities;
Geography Dept., St. Cloud Research, Instruction
Public Utilities;
Minnesota Power Utility Mapping
A detailed inventory of current and future uses of GPS have been
compiled and are shown in Appendixes A & B.
The inventory shows that besides IVHS there are few other applications
that absolutely require RTCM and many others that would benefit from
the reduced need for data processing.
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VISION OF FUTURE USES
FOR GPS
When a person or group tries to see into the future regarding new
technologies, it is often a guess. Applications seem to be limited
only to the creativity of the human mind. Technology now is
advancing rapidly in the areas of miniaturization and the
integration of systems on computer boards making it difficult to
see very far into the future.
However, in the area of DGPS RTCM, we feel that the future holds an
expanding area of applications across a side area of disciplines.
This type of GPS will be used to determine positions, guide all
navigating, and be use for most all motion analysis on the surface
of the earth. Recently, the US Secretary of Transportation and IVHS
America both endorsed GPS as the positioning method of choice. GPS
can be used for applications from the professionals solving
technical problems to normal everyday getting around town; from
locating and managing resources, managing facilities, constructing
maps and structures to directing moving vehicles and planes.
As we implement this capability across wider areas of the surface
of the earth, we can expect broader use, more applications, and a
general permeation in becoming more and more a part of our everyday
lives. This technology has often been billed as the "next
utility". From where we stand, this is a prophetic statement.
PILOT PROJECT
PLAN
The plan is to test the feasibility of implementing a GPS base station
that all governmental units can access for differential GPS
applications. This first base station serves differential GPS post-
processing needs, and will help the State of Minnesota better define
the plan and specifications for installing additional base stations
throughout the state. In addition to addressing the post-processing
needs, this base station will serve as a pilot project for research,
testing and development of "real-time" radio broadcasting of the
differential GPS corrections to receivers that are linked to a radio
capable of receiving the correction messages.
17
TRATEGY
The strategy consisted of forming a task force including
representatives from state and federal government who had expertise
and involvement in applications of GPS within their agencies. The
charge to the task force was to develop a plan for implementation of
GPS base stations utilizing Mn/DOT's existing communications network.
Initial funding needed for hardware and software purchases was to come
from fiscal year 1993 funds through the Mn/DOT Council for Geographic
Information. Expenditures were not to exceed $50,000.
The task force met every two weeks from February through July of 1993.
During the first two meetings, three goals were identified:
1. Make GPS post-processing data available through a computer
network
2. Implement testing of a Real Time Correction Message (RTCM)
broadcasting code-phase differential GPS (DGPS)
corrections for 1-5 meter accuracy needs.
3. Research the requirements needed for higher accuracy (sub-
meter) needs obtainable by carrier-phase data also
available through the GPS RTCM base station.
STAGING
After considerable discussion, the task force agreed to upgrade the
existing GPS base station located at the Minnesota Department of
Health (MDH) on the University of Minnesota Campus in Minneapolis
(East Bank). The base station data is currently available on the
state computer network (Internet) for postprocessing of code-phase GPS
data--for 1-5 meter accuracy needs. The upgrades also included
purchasing hardware, software, and firmware necessary to accomplish
goals number two and three shown above. Goal number one would be
enhanced by purchasing equipment necessary to add the carrier-phase
data for post-processing.GPS data for submeter accuracy needs. It was
also stated early in the discussions that the MDH is open to the
option of moving the base station to any location that would better
serve the three goals of this task force.
18
Goal number two soon became the focus of the task force since this
would serve the needs of most current and future applications of GPS
for positioning and navigating at the 1-5 meter accuracy level. The
major obstacle for broadcasting code-phase differential GPS
corrections was determining the statewide radio frequency and location
of the radio broadcast antenna. To accomplish this goal, the support
of the electrical engineers from the Mn/DOT Office of Electronic
Communications was critical to the task force. With their support,
the following steps were taken to implement goals number two.
. the DNR Minerals Division provided the statewide radio
frequency of 151.445 MHZ for broadcasting of GPS differential
corrections.
. the Minneapolis First Bank building was selected for the site
of the DGPS RTCM broadcasting tower, and a lease agreement was
reached. A 350 watt transmitter will have an estimated range of
60+ miles. This should cover the entire Minneapolis/St. Paul
seven county area. We will test for distance coverage and
accuracy of the RTCM.
. equipment was purchased to transfer the GPS data collected at
the MDH to the radio broadcast tower on the First Bank building
via a telephone modem.
Goal number three which addresses the needs of higher accuracy
applications (submeter) for real-time positioning or navigating has
fewer users but a large payoff. Currently, to position objects or
navigate at the high accuracy level, surveying equipment and expertise
are needed. This is labor intensive and costly. The equipment and
staging used for goals number one and two will allow for the
accomplishment of goal number three.
COSTS
* none of these costs reflects the hours of personnel time provided
by the various agencies in this task force. These numbers are
hardware and software only.
Below is a summary of the hardware and software costs for this pilot
project. For a diagram of these items, see the following page (Figure
4).
19
Click HERE for graphic.
existing MDH GPS base 15,000
upgrades to MDH GPS base 5,000
transmitting antenna set-up 2,000
. antenna building lease (12 months @ 500/mo) 6,000
cables and connectors 200
350 transmitter 14,500
GPS base receiver with modem 3,000
signal isolator 1,300
modems (2) to connect with MDH 1,600
hand-held test radio receivers (for
use with handheld GPS equip (2 @ 2700/ea) 5,400
miscellaneous fees and parts 1000
Motorola training and installation 5000
Total: $60,000
OUTCOMES
. since Wisconsin GPS task force working on higher accuracy
capabilities for post-processing, we concentrated on Real Time
Correction Messaging, and shared data.
. upgraded MDH GPS base to carrier-phase
. established a DGPS RTCM broadcasting base station on top of the
First Bank building in Minneapolis
. made the current MDH DGPS data available on Internet to all state
agencies (this was of immediate use to other state agencies).
. created the only document listing current GPS applications and
equipment in Minnesota State and Federal Governments
. developed a vision for the future of GPS related to the agencies
involved.
. currently attempting to get GPS equipment on the "state contract"
so purchasing in easier, less costly, faster, and equipment is
standardized.
. see Recommendations section in this report
. see Problems/Issues section in this report
. began partnering with other agencies to share knowledge, work
loads, reduce redundant efforts, standardize procedures, pool
funds, and staff time.
. began partnering with private entities to coordinate development
efforts to reduce unnecessary proprietary methods so public and
private entities benefit.
20
PROBLEMS NEEDING DECISIONS
During the implementation of the pilot study DGPS transmit site, and
the planing of a state wide differential DGPS broadcast system, the
following issues arose as items to be addressed. The problems
described below will need to be resolved in order to assure that a
statewide system is planned, implemented, and maintained in a manner
that meets the needs of the proposed users, and provides the desired
service.
The items identified fall into three categories; Technical,
Administrative, and Standards. This task force, or a similar
successor group, should be able to resolve the technical issues. It
is thought that standards issues can be resolved in mid-level multi-
agency workshops sponsored+ by the Governor's Council on Geographic
Information. The administrative issues reach into areas that can only
by resolved at the highest levels because they are the prerogative of
administrators, involving policy and politics.
Below is a list of identified long-range problems and a brief
discussion of each.
Technical issues:
. Internet storage media/archive capacity needs to be
researched. A network for access of this data needs to be
defined.
. What vertical accuracy requirements can be met by GPS.
. Multiple site use - Simulcast interference.
. Multiple frequency use. Regional systems on different
frequencies.
. Number of GPS base sites. Multiple transmit sites with
individual GPS receivers. Multiple transmit sites with one
central GPS receiver.
. Data handling limitations for two way transmissions.
Database management.
. Identify interface accessories for differing mobile and
portable radio equipment.
21
. For multiple DGPS fixed or mobile base stations, a method
needs to be developed to account for radio interference of
close proximity stations operating at the same frequency.
. In view of Federal Aviation Administration's (FAA) and US
Coast Guard's real-time DGPS base station development, how
many DGPS sites do we need for statewide availability?
. Is it technically feasible for the same real-time DGPS base
stations to provide the ó 5 meter accuracy data for the
separate US Coast Guard, US Army COE, FAA, IVHS (navigation)
applications, and provide the real-time and post-processing
data for GIS applications.
. What are the accuracy limitations of real-time code phase
data being broadcast from a base station as far away as 50
miles (i.e. can an over-determined solution of code phase
data provide submeter accuracy for a position being
collected 50 miles from the base station)?
. Are there public facilities and personnel distributed
throughout the state that are capable and willing to provide
daily maintenance and data storage for the post-processing
applications (for both ó5 and ó 1 meter applications)?
Administrative issues:
. Who is responsible for the system?
. Personnel needed to keep system functional.
. Maintenance and training of technical support staff.
. Equipment upgrades/replacement.
. System growth.
. Is a user charge needed? Who sets the fees? How will the
service be advertised, and monitored?
22
. Are there liabilities with allowing others to use the data?
. Who will be accountable for system accuracy and reliability
(performance).
. Should we allow our sites to be used as FAA certified GPS
base sites? What are the requirements associated with
certification? Should we propose this use or wait to be
approached.
. Will existing radios be used for GPS applications? Will
additional radios be purchased for use in GPS applications.
. The number of DGPS users and types of DGPS uses need to be
identified. Priority transmit locations need to be
identified for a system expansion plan.
. Access to this DGPS data (who & how)
. Who should be responsible for making statewide DGPS
available in real-time? This involves:
- integrity/reliability
- maintenance (equipment upgrades/replacement, user
training, support staff training)
- growth (priority locations,
advertisement/promotion)
- funding (free? user fees? annual fees?)
. Who should address public safety issues which involve
integrity of DGPS used in navigation (for automated flying,
shipping, driving)?
. How do we pursue the possibility of "piggybacking" on FAA
or USCG DGPS bases to make them more widely available and
usable (i.e. rebroadcast their signal forground/land use)?
. Should there be a fee assessed for users of the real-time
DGPS broadcast? Is this a public service?
. Real-time DGPS applications for facilities management will
have a tremendous impact on how utility companies collect
positions or
23
ocate their underground utilities (especially in public right-of-way)
when using submeter accuracy equipment and techniques. How should the
utility companies partner with others in the implementation of real-
time DGPS?
. Assuming DGPS data should be archived for post-processing
needs, how long should it be archived? Who should do this?
Where should the data be kept?
. Prepare an MOU, policy or whatever is necessary to
facilitate and encourage agencies to work together and with
private partners on issues.
Standards Issues:
. An accepted datum standard must be defined
. Will a state contract for equipment be established? Will
minimum equipment standards be developed for users of the
system?
. Quality assurance procedures must be developed
. Standard codes for positional accuracy to be used in
statewide databases must be established
. Develop a minimum list of GPS equipment features for all
agencies to follow when purchasing GPS equipment for certain
application.
. Specifications for GPS receivers need to be developed that
require automatic notification of accuracy. Data loaded to
a data collector should include Lat/Long, elevation, and
accuracy. A warning for the field user should be included
when the data are out of a selected accuracy range.
. Because of obstructions, radio interference and satellite
integrity, there will always be situations where GPS can't
be used. There should be standards and/or procedures
developed to handle these gaps in GPS data collection.
24
Quality assurance procedures must be developed.
. The accepted horizontal datum standard is North American
Datum of 1983 (NAD83). The accepted vertical datum is
National Geodetic Vertical Datum of 1929 (NGVD29) or North
American Vertical Datum of 1988 (NAVD88) using the most
current geoid model. This needs to be known and used to
obtain the best data from the GPS.*
*if calculating elevations, the DGPS signal is broadcast in
NAD83 (gives height above ellipsoid) which can be converted
to height above sea level (geoid is based on NGVD29 or
NAVD88) using the current geoid model (currently "Geoid
93"). See Figure 3.
25
ITEMS LEARNED FROM
PILOT PROJECT
. It is not a black box technology yet. The users want a turn-key
solution, but the right combination of separate boxes and cables
remains to be resolved.
. Signal range for digital data (800 feet above ground, 350 watt
transmitter) is about one-half the range for voice data.
. Partnerships are important to reduce redundant efforts and share
resources (money, equipment, personnel, and knowledge).
. We are working within a technological window no larger than 12
months in size. Significant changes will occur outside this
window; hence anything we recommend about technology will be
significantly outdated within 12 months.
. There are several methods for transmitting thedifferential corrections. There are advantages and
disadvantages to each. Here is a brief list:
. Radio frequency broadcast like this project
demonstrated -
. Advantages: one frequency for all equipment, total
control over signal.
. Disadvantages: multiple broadcast towers have to
constantly
. Broadcast using side-bands of existing radio stations -
. Advantages: others monitor broadcast integrity, can
use other's broadcast equipment, no overlapping
coverage areas with same frequency.
. Disadvantages: at mercy of many radio station's fee
structures; need to tune to different frequencies in
different areas.
26
. Use one of the many real-time DGPS services which
broadcast the message via pager networks or satellite.
. Advantages: others monitor broadcast integrity, can
use other's broadcast equipment.
. Disadvantages: at mercy of private fee structure;
these methods haven't been proven for consistency of
data.
. The greater the required positional accuracy (ó5 meter vs ó1
meter vs ó 1 cm) the smaller the number of users. This may
suggest that ó 5 m or ó 1 m be provided statewide, and ó 1cm be
handled locally by the users as needed.
. As quickly as technology improves to allow greater accuracy for
the same cost, inevitably the beneficiaries conjure a need for
that greater accuracy.
. Multiple uses and development efforts (utilities, counties, drug
enforcement, IVHS, fleet management) are hard to coordinate but
seem to group into four areas -
1. accuracy required is > 100 m (non-DGPS)
2. ó5m
3. ó1 m
4. ó1 cm
. The antenna on the receiving unit is at least as important as
the sending unit -
. rubber duck" (10 cm' black, rubber) antenna received to
approximately 20 miles.
. "roof antenna" (1 m metal, magnetic) on car to
approximately 45 miles.
. "pole" (3 m range pole) to approximately 60 miles.
. More and more users want real-time DGPS.
27
. Navigation requires real-time DGPS.
. Real-time DGPS takes less time than post-processing.
28
RECOMMENDATIONS
. Get GPS equipment on " state contract" or allow purchasing
from Government Service Agreement (GSA).
. Decide who will be long-term equipment maintenance agency(s).
. Transfer of MDH GPS base station to another agency (Mn/DOT?).
. Concentrate efforts on providing sub-meter accuracy, code-phase
(ó 1 m), real-time corrections for underground utility location
and other infrastructure applications.
. Monitor the development of FM side-band technology (RDBS) vs a
dedicated radio frequency that was used for the pilot project.
Current incompatibilities need to be resolved.
. Keep track of satellite broadcast technology for real-time DGPS.
. Where possible, use a submeter base station since it will also
serve the ó 5 m users and costs about the same.
. Keep track of FAA's activities. They may have statewide ó 6 m
available for at least aircraft in 1995-96. We may be able to
rebroadcast their signal for ground/land use.
. Continue this task force with a new charge something like ...
Study options and recommend the most economical and practical
solution to providing real-time DGPS statewide Identify costs for
testing the plan once plan is developed. Develop and conduct
joint projects (partnerships). Have this task force report about
current issuers and trends every six months to the Governor's
Council on Geographic Information.
. Provide the above task force formal involvement with all
initiatives where GPS technology will be used.
29
. Seek to develop agreements with county and municipal governments
to share the cost and development of running base stations or ask
the legislature to consider base station operations as a line
item, defining the agency responsible for the administration.
. Seek to increase all agencies' funding of DOT's Office of
Electronic Communications to cover the costs of operating base
stations statewide.
. Create a policy that states any agency creating a new DGPS base
station will make the data files available via Internet until
real-time is available statewide. The central coordination for
these data files could be through the Minnesota Land Management
Information Center (LMIC).
. Focus on getting real-time DGPS available in population centers
(Metro, Duluth, Rochester, Brainerd/St. Cloud) over the next two
to three years. As submeter real-time DGPS becomes available
nationally (such as through the FAA) and technology improves,
convert the former stations to use for centimeter accuracy work -
- maybe as roving stations for project/area specific work.
. Try to find an additional statewide frequency for use by the
roving real-time DGPS base stations.
. Continue to track DGPS private service providers' DGPS
positional accuracy and costs. Currently, costs are much too
high to warrant state agencies (with 1000's of users) using
them (see Table 1 on next page).
30
GLOSSARY
Almanac: The very approximate orbit used to support GPS
pre-survey planning. The almanac is used to determine rise-set
times, etc. A high efficiency, comparative low-accuracy,
analytical technique is sufficient to generate the almanac. he
navigation message transmitted by each GPS satellite, contains
an almanac for every other satellite in the GPS constellation.
AM: Measurement wave that is amplitude modulated.
Ambiguities: The uncertainty in the number of measurement waves
transmitted from the satellite to the receiver.
Anywhere Fix: The ability of a receiver to start position
calculations without being given an approximate location and
approximate time.
Argument of perigee: The angle or arc from the ascending node to
the closest approach of the orbiting body to the focus or
perigee point, as measured at the focus of an elliptical
orbit, in the orbital plane in the direction of motion of the
orbiting body.
Argument of latitude: The sum of the true anomaly and the
argument of perigee.
Ascending node: The point at which an object's orbit crosses the
reference plane (e.g., equatorial plane) from south to north.
Azimuth: The direction of a line, in the horizontal plane,
measured clockwise from North.
Bandwidth: A measure of the information-carrying capacity of
a signal (the range of frequencies in a signal), expressed as
the width of the spectrum of that signal (frequency domain
representation) in Hertz.
Base Station: A stationary GPS receiver.
Baseline: The three-dimensional vector distance between a pair
of stations for which simultaneous GPS data has been collected
& processed with DGPS.
i
Beat frequency: Either of the two additional frequencies obtained
when signals of two frequencies are mixed. The beat
frequencies are equal to the sum or difference of the original
frequencies.
Bias: See Integer Bias Terms.
Binary biphase modulation: Phase changes of either 0 or 180
degrees on a constant frequency carrier (representing a binary
0 or 1 respectively). GPS signals are biphase modulated.
Binary pulse code modulation: Pulse modulation using a string of
binary numbers (codes). This coding is usually represented by
ones and.zeros with definite meanings assigned to them, such
as changes in phase or direction of a wave.
Block I Satellites: Five operational satellites, from the
original experimental satellites.
Block II: 21-24 satellites, expected to be in full operation by
the mid 1990's, deployed in six orbital planes inclined 550 to
the equator. Like the Block I satellites, they will be in a
near circular orbit at an altitude of approximately 20,000
kilometers (12,000 miles) with an orbital period of 11 hours
58 minutes.
Bluebook: A slang term derived from a blue NGS reference book.
The book contains information and formats required by NGS for
survey data that is submitted to be considered for use in the
national network.
Broadcast Ephemeris: The predicted GPS satellite positions that
are contained within the navigation message which is
transmitted by each GPS satellite. Computed from
approximately one week of data from the five tracking
stations.
C/A code: The Coarse/Acquisition (or Clear/Acquisition) code
modulated onto the GPS Ll signal. This code is a sequence of
1023 pseudorandom binary biphase modulations on the GPS
carrier at a chipping rate of 1.023 Mhz, thus having a code
repetition period of one millisecond. This code was selected
to provide good acquisition properties.
Carrier frequency: The frequency of the umnodulated fundamental
output of a radio transmitter.
ii
Carrier: A radio wave having at least one characteristic (such
as frequency, amplitude, phase) which may be varied from a
known reference value by modulation.
Carrier-aided tracking: A signal processing strategy that uses
the GPS carrier signal to achieve an exact lock on the pseudo
random code. More accurate than standard approach.
Carrier-beat-phase: Phase comparison that is performed on the
wavelength carrier.
Celestial equator: The great circle that is the projection of the
Earth's geographical equator of rotation onto the celestial
sphere. Its poles are the North and South Celestial Poles.
Celestial meridian: That vertical circle through the elevated
celestial pole. It also passes through the other celestial
pole, the astronomical zenith, and the nadir.
Channel: A channel of a GPS receiver consists of the radio
frequency, digital hardware, and the software, required to
track the signal from one GPS satellite at one of the two GPS
carrier frequencies.
Chip: The length of time to transmit either a zero or a one in a
binary pulse code.
Chip rate: Number of chips per second (e.g., C/A code = 1.023
Mhz).
Clock bias (clock offset): The difference between the clock's
indicated time and true universal time.
Code division multiple access (CDNU): A method of frequency re-
use whereby many radios use the same frequency but with each
one having a separate and unique code. GPS uses CDMA
techniques with Gold's codes for their unique cross-
correlation properties.
Control segment: A world-wide network of GPS monitoring and
control stations that ensure the accuracy of satellite
positions and their clocks.
Conventional international origin (CIO): Average position of
Earth's rotation axis during the years 1900-1905.
iii
Correlation-type channel: A GPS receiver channel which uses a
delay lock loop to maintain an alignment ' (correlation peak)
between the replica of the GPS code generated in the receiver
and the received code.
Cycle-slip: Interruption of the signal between the satellite and
receiver, causing the receiver to lose track of the integer
number of measurement waves.
Data message: A message included in the GPS signal which reports
the satellite's location, clock corrections and health.
Included is rough information on the other satellites in the
constellation.
Deflection of the vertical: The angle between the normal to the
ellipsoid and the vertical (true plumbline). Since this angle
has both a magnitude and a direction, it is usually resolved
into two components: one in the meridian and the other
perpendicular to it in the prime vertical.
Delay lock: The technique whereby the received code (generated
by the satellite clock) is compared with the internal
code(generated by the receiver clock) and the latter is
shifted in time until the two codes match. Delay lock loops
can be implemented in several ways; tau dither and early-
minus-late gating.
Delta pseudorange: See reconstructed carrier phase.
DGPS: Differential GPS (see Differential positioning).
Differential (relative) positioning (DGPS): Determination of
relative coordinates of two or more receivers which are
simultaneously tracking the same satellites. Dynamic
differential positioning is a real-time calibration technique
achieved by sending corrections to the roving user from one or
more monitor stations. Static differential GPS involves deter
mining baseline vectors between airs of receivers.
Differential processing (DGPS): GPS measurements can be
differenced between receivers, satellites, and epochs.
Although many combinations are possible, the present
convention for differential processing of GPS phase
measurements is to take differences between receivers (single
difference), then between satellites (double difference), then
between measurement epochs (triple difference).
iv
Differential techniques:
Single difference: Two receivers tracking the same satellite
at the same time. The difference in carrier measurements
reduces some of the effect of error, especially satellite
clock error.
Double difference: Two receivers observing two satellites at
the same time, allowing for easy determination of cycle slips.
Triple difference: Two receivers observing two satellites at
two different times, allowing the phase ambiguity to be
eliminated.
Dilution of Precision (DOP): The multiplicative factor that
modifies ranging error. It is caused solely by the geometry
between the user and his set of satellites, given by the expre
ssion DOP = SQRT TRACE (AA) where AA is the design matrix for
the instantaneous position solution (dependent on satellite-
receiver geometry). The DOP factor depends on the parameters
of the position-fix solution. Standard terms for the GPS
application are:
GDOP Geometric (three position coordinates plus clock
offset in the solution) GDOP2 = PDOPI2 + TDOP2.
PDOP Position (three coordinates)
HDOP Horizontal (two horizontal coordinates)
VDOP Vertical (height only)
TDOP Time (clock offset only) RDOP Relative (normalized
to 60 seconds)
DNR: Minnesota Department of Natural Resources.
Doppler shift: The apparent change in the frequency of a signal
caused by the relative motion of the transmitter and receiver.
Doppler-aiding: A signal processing strategy that uses a
measured doppler shift to help the receiver smoothly track the
GPS signal. Allows more precise velocity and position
measurement.
Double-difference method: A method to determine that set of
ambiguity values which minimizes the variance of the solution
for a receiver pair baseline vector.
Dynamic positioning: Determination of a timed series of sets of
coordinates for a moving receiver, each set of coordinates
being determined from a single data sample, and usually
computed in real time.
v
Earth-centered earth-fixed - (ECEF): Cartesian coordinate system
where the X direction is the intersection of the prime
meridian (Greenwich) with the equator. The vectors rotate
with the earth. Z is the direction of the spin axis.
Easting: A colloquialism for "longitude.
Eccentric anomaly E: The regularizing variable in the two-body
problem. E is related to the mean anomaly M by Kepler's equat
ion: M = E - e.sine (e stands for eccentricity).
Eccentricity: The ratio of the distance from the center of an
ellipse to its focus to the semimajor axis.
e = (I - b2/a2)-1/2 where a and b are the semimajor and
semiminor axes of the ellipse.
Ecliptic: The earth-sun orbital plane. North is the direction of
the system's angular momentum. Also called the ecliptic pole.
Elevation: Height above mean sea level. Vertical distance above
the geoid.
Elevation Mask Angle: That angle below which we recommend that
you do not track satellites. Normally set to 15 degrees to
avoid interference problems caused by buildings and trees and
multipath errors.
Ellipsoid: In geodesy, unless otherwise specified, a mathematical
figure formed by revolving an ellipse about its minor axis.
It is often used interchangeably with spheroid. Two
quantities define an ellipsoid; these are usually given as the
length of the semimajor axis, a, and the flattening, f = (a -
b)/a, where b is the length of the semiminor axis. Prolate
and triaxial ellipsoids are invariably described as such.
Ellipsoid height: The measure of vertical distance above the
ellipsoid. Not the same as elevation above sea level. GPS
receivers output position -fix height in the WGS-84 datum.
Ephemeris: A list of (accurate) positions or locations of
satellite positions as a function of time. Available as
"broadcast ephemeris" or as postprocessed "precise ephemeris."
poch: Measurement interval or data frequency, as in making
observations every 15 seconds. Loading data using 30-second
epochs means loading every other measurement.
FAA: Federal Aviation Administration.
Fast-switching channel: A single channel which rapidly samples a
number of satellite ranges. "Fast" means that the switching
time is sufficiently fast (2 to 5 milliseconds) to recover the
data message.
FGCS: Federal Geodetic Control Subcommittee.
Flattening: f = (a - b)/a = 1-(l - e 2)11 a = Semimajor axis b =
Semiminor axis e = Eccentricity
Frequency spectrum: The distribution of amplitudes as a function
of frequency of the constituent waves in a signal.
Frequency band: A range of frequencies in a particular region of
the electromagnetic spectrum.
Fundamental frequency: The fundamental frequency used in GPS is
10.23 Mhz. The carrier frequencies L1 and L2 are integer
multiples of this fundamental frequency. L1 = 154F = 1575.42
MHz L2 = 12OF 1227.60 Mhz.
GDOP: Geometric Dilution of Precision. (see Dilution of
Precision)
Geocenter: The center of the earth.
Geodetic datum: A mathematical model designed to best fit part or
all of the geoid. It is defined by an ellipsoid and the
relationship between the' ellipsoid and a point on the
topographic surface established as the origin of datum. This
relationship can be defined by six quantities, generally (but
not necessarily) the geodetic latitude, longitude, and the
height of the origin, the two components of the deflection of
the vertical at the origin, and the geodetic azimuth of a line
from the origin to some other point. The GPS uses WGS-84,
which see.
vii
Geoid Height: The distance, N, at a point between the ellipsoid
and the geoid. If the geoid is below the ellipsoid, as it is
for NAD 83 in the continental U.S., the geoid height is
negative.
Geoid: The particular equipotential surface which coincides with
mean sea level, and which may be imagined to extend through
the continents. This surface is everywhere perpendicular to
the force of gravity.
GMT: Greenwich Mean Time. Also called Universal Time (UT), which
is the time at the meridian of O' longitude.
GPS: Global Positioning System. The GPS consists of the NAVSTAR
satellites (21 satellites plus 3 spares) in six different
orbits, five monitor stations, and the user community.
GPS ICD-200: The GPS Interface Control Document is a government
document that contains the full technical description of the
interface between the satellites and the user. GPS receivers
must comply with this specification if they are to receive and
process GPS signals properly.
Gravitational constant: The proportionality constant in Newton's
Law of Gravitation: G = 6.672 x 10-11 Nm2/Kg2
Handover word: The word in the GPS message that contains
synchronization information for the transfer of tracking from
the C/A to P code.
HDOP: Horizontal Dilution of Precision. See DOP and PDOP.
HOW: Handover word. The word in the GPS message that contains
time synchronization information for the transfer from the C/A
code to the P code.
Inclination: The angle between the orbital plane of a body and
some reference plane (e.g., equatorial plane).
INS: Inertial navigation system, which contains an inertial
measurement unit (IMU).
viii
Integer Bias Terms: The receiver counts the radio waves from the
satellite, as they pass the antenna, to a high degree of
accuracy. However, it has no information on the number of
waves to the satellite at the time it started counting. This
unknown number of wavelengths between the satellite and the
antenna is the integer bias term.
Integrated Doppler: A measurement of Doppler shift frequency or
phase over time.
Ionosphere: The band of charged particles 80 to 120 miles above
the earth's surface.
Ionospheric delay: A wave propagating through the ionosphere
[which is a nonhomogeneous (in space and time) and dispersive
medium experiences delay. Phase delay depends on electron
content and affects carrier signals. Group delay depends on
dispersion in the ionosphere as well, and affects signal
modulation (codes). The phase and group delay are of the same
magnitude but opposite sign.
ipar soln: Values giving the difference in each of delta X, delta
T, delta Z vector components.
IVHS: Intelligent Vehicle Highway System (also: Intelligent
Vehicle Highway Society).
JPO: Joint Program Office for GPS located at the USAF Space
Division at El Segundo, California. The JPO consists of the
USAF Program Manager and Deputy Program Managers representing
the Army, Navy, Marine Corps, Coast Guard, Defense Mapping
Agency and NATO.
Kalman filter: A numerical method used to track a time-varying
signal in t he presence of noise. If the signal can be
characterized by some number of parameters that vary slowly
with time, then Kalman filtering can be used to tell how
incoming raw measurements should be processed to best estimate
those parameters as a function of time.
ix
Keplerian orbital elements: Allow description of any astronomical
orbit:
a: semimajor axis
e: eccentricity
o: argument of perigee
1: right ascension of ascending node
i: inclination
t: true anomaly
Kinematic surveying: A form of continuous differential carrier
phase surveying requiring only short periods of data
observations. Operational constraints include starting from
or determining a known baseline, and tracking a minimum of
four satellites. One receiver is statically located at a
control point, while others are moved between points to be
measured.
L-band: The group of radio frequencies extending from 390 Mhz to
1550 Mhz. The GPS carrier frequencies (1227.6 Mhz and 1575.42
Mhz) are in the L band.
L1, L2: The primary L-band signal radiated by each NAVSTAR
satellite at 1575.42 Mhz. The L1 beacon is modulated with the
C/A and P codes, and with the NAV message. L2 is centered at
1227.60 Mhz and is modulated with the P code and the NAV
message.
Lane: The area (or volume) enclosed by adjacent lines (or
surfaces) of zero phase of either the carrier beat phase
signal, or if the difference between two carrier beat phase
signals. On the earth's surface a line of zero phase is the
locus of all points for which the observed value would have an
exact integer value for the complete instantaneous phase
measurement. In three dimensions, this locus becomes a
surface.
Latitude: The angular distance a line extends in a north or south
direction from the equator.
Longitude: The angular distance east or west measured by the arc
between two meridians, one of which passes through any given
point and the other through a point chosen as standard of
reference.
Mean anomaly: M = n (t - T) where: n is the mean motion, t is the
time and T is the instant of perigee passage.
x
Mean motion: n = 2/P where P is the period of revolution.
(Megahertz--Hertz): The international unit of frequency, equal to
one cycle per second. Megahertz - one million cycles per
second.
Microstrip antenna: A two-dimensional, flat, precisely cut piece
of metal foil glued to a substrate.
MNDOT: Minnesota Department of Transportation.
Monitor station: Worldwide group of stations used in the GPS
control segment to monitor satellite clock and orbital
parameters. Data collected here is linked to a Master Station
where corrections are calculated and controlled. These data
are uploaded to each satellite at least once per day from an
Upload Station.
Multichannel receiver: A receiver containing many independent
channels. Such a receiver offers highest SNR because each
channel tracks one satellite continuously.
Multipath: Interference similar to "ghosts" on a television
screen which occurs when GPS signals arrive at an antenna
having traversed different paths. The signal traversing the
longer path will yield a larger pseudo range estimate and
increase the error. Multiple paths may arise from reflections
from structures near the antenna.
Multipath error: A positioning error resulting from interference
between radio waves which have traveled between the
transmitter and the receiver by two paths of different
electrical lengths. Usually caused by one path being bounced
or reflected.
Multiplexing receiver: Also called switching receiver. Same
channel switches from one satellite to another.
Multiplexing channel: A receiver channel which is sequenced
through several satellite signals (each from a specific satellite
and at a specific frequency) at a rate which is synchronous with
the satellite message bit-rate (50 bits per second, or 20
milliseconds per bit). Thus, one complete sequence is completed
in a multiple of 20 milliseconds..
NAD 27: North American Datum, 1927.
xi
NAD 83: North American Datum, 1983.
NAVDATA: The 1500-bit Navigation Message broadcast by each
satellite at 50 bps on both L1 or L2 beacons. This message
contains system time, clock correction parameters, ionospheric
delay model parameters, and the vehicle's ephemeris and
health. This information is used to process GPS signals to
obtain user position and velocity.
NAVSTAR: NAVigation Satellite Timing and Ranging. The acronym
used to describe the Department of Defense GPS satellite
system built by Rockwell International.
NGS: National Geodetic Survey.
Northing: A colloquialism for "latitude."
Observing session: The period of time over which GPS data is
collected simultaneously by two or more receivers.
Outage: The occurrence in time and space of a GPS dilution of
precision value exceeding a specified maximum.
Overdetermined: A term used in the adjustment and analysis of
data by leastsquares method. An overdetermined condition
exists when the analyst applies more than the minimum number
of constraints necessary to keep the solution from becoming
singular. A singular condition exists when the determinant of
a matrix is zero. This can be tested by dividing all, the
elements in a row by their corresponding elements in another
row. If the quotient is the same in all cases then the matrix
is singular. (Example: reading eight satellites gives eight
equations with only four unknowns. Obviously this doesn't
lead to only one solution.)
P-Code: The Precise (or protected) 30-meter measurement wave of
10.23 Mhz that is modulated onto the L1 and L2 carriers and
repeats itself about every 267 days.
Parity error: A digital message is composed of Is and Os.
Parity can be defined as the sum of these bits within a word
unit. A parity error results when one of the bits is changed.
so that the parity calculated at reception is not the same as
it was at transmission of the message.
xii
PDOP: Positional Dilution of Precision. A number that describes
the geometric condition of the satellites with respect to a
ground station.
Perigee: That point in a geocentric orbit when the geometric
distance is a minimum. The closest approach of a body.
Phase: A portion of a complete cycle of a wave.
Phase lock: The technique whereby the phase of an oscillator
signal is made to follow exactly the phase of a reference
signal by first comparing the phases of the two signals, and
then using the resulting phase difference signal to adjust the
reference oscillator frequency to eliminate phase difference
when the two signals are next compared.
Phase observable: See reconstructed carrier phase.
Phase comparison: A procedure that measures the phase of one wave
and that of another at the same time.
Phase difference: The time in electrical degrees by which one
wave leads or lags another.
Point positioning: A geographic position produced from one
receiver in a stand-alone mode. At best, position accuracy
obtained from a stand-alone receiver is 15-25 meters,
depending on the geometry of the satellites.
Polar motion: Motion of the instantaneous axis of the rotation
of the Earth with respect to the solid body of the Earth.
Irregular but more or less circular motion with an amplitude
of about 15m and a main period of about 430 days (called
Chandler Wobble).
Positioning: Determination of a position (usually a GPS antenna)
with respect to a coordinate system (WGS 84, UTM, State Plane,
etc.).
Precise ephemeris: A post-processed ephemeris, more accurate
than the broadcast ephemeris. It defines the satellite
positions during the time period of the observations.
Precise positioning service (PPS): The highest level of military
dynamic positioning accuracy that will be provided by GPS,
based on the dual frequency P code and having high anti-jam
and anti-spoof qualities.
xiii
Prime vertical: The vertical circle perpendicular to the
celestial meridian.
PRN: Pseudorandom noise, a sequence of digital Is and Os which
appear to be randomly distributed like noise, but which can be
exactly reproduced. Each NAVSTAR satellite has its own unique
C/A and P pseudorandomnoise codes.
Pseudo-random code: A signal with random-noise like properties.
It is a very complicated but repeated pattern of l's and O's.
Pseudolite: A ground-based GPS transmitter station which
broadcasts a signal with a structure similar to that of an
actual GPS satellite.
Pseudorange: A distance measurement based on the correlation of a
satellite transmitted code and the local receiver's reference
code, that has not been corrected for errors in
synchronization between the transmitter's clock and the
receiver's clock.
Pseudorange difference: See reconstructed carrier phase.
Range rate: The rate of change of range between the satellite
and receiver. The range to a satellite changes due to
satellite and observer motions. Range rate is determined by
measuring the Doppler shift of the satellite beacon carrier.
RDOP: Relative Dilution of Precision. See DOP.
Real-time: immediate or instantaneous. In GPS practice (within 10
seconds of time).
Reconstructed carrier phase: The difference between the phase of
the incoming Doppler-shifted GPS carrier and the phase of a
nominally constant reference frequency generated in the
receiver. For static positioning, the reconstructed carrier
phase is sampled at epochs determined by a clock in the
receiver.
. it changes according to the continuously integrated
Doppler shift of the incoming signal, biased by the
integral of the frequency offset between the satellite
and receiver reference oscillators.
. it can be related to the satellite-to-receiver range,
once the initial range (or phase ambiguity) has been
determined. A change in the satellite-to-receiver range
of one wavelength of the GPS carrier (19
xiv
cm for L1) will result in a on-cycle change in the phase
of the reconstructed carrier.
Relative positioning: The process of determining the relative
difference in position between two marks with greater
precision than that to which the position of a single point
can be determined. Here, a receiver (antenna) is placed over
each spot and measurements are made by observing the same
satellite at the same time.- This technique allows
cancellation (during computations) of all errors which are
common to both observers, such as satellite clock errors,
propagation delays, etc. See also Translocation and
Differential Navigation.
Relative navigation: A technique similar to relative positioning
except that one or both of the points may be moving. The
pilot of a ship or aircraft may need to know his position
relative to a harbor or runway. A data link is I y used to
relay the error terms to the moving vessel to allow real-time
navigation.
Right ascension of ascending node: The angular distance measured
from the vernal equinox, positive to the east, along the
celestial equator to the ascending node. Typically denoted by
a capital omega. Used to discriminate between orbital planes.
RINEX: Receiver INdependent EXchange format. A set of standard
definitions and formats to promote the free exchange of GPS
data and facilitate the use of data from any GPS receiver with
any software package. The format includes definitions for
three fundamental GPS observables: time, phase, and range. A
complete description of the RINEX format is found in the
Commission VIII International Coordination of Space Techniques
for Geodesy and Geodynamics "GPS" BULLETIN," May-June, 1989.
Roving Receiver: Transported GPS receiver located in an "unknown"
location.
RTCM: Real Time Correction Message--used to counteract selective
availability. (also sometimes used for Radio Technical
Commission for Maritime Services--Commission set up to define
a differential data link to relay GPS correction messages from
a monitor station to a field user. RTCM SC-104
recommendations define the correction message format and 16
different correction message types)
xv
Satellite constellation: The arrangement in space of a set of
satellites.
Satellite window: When the satellites are above the observer's
horizon and positioned such that they can be tracked by the
receiver(s).
SATNAV: A local term referring to use of the older TRANSIT
system for satellite navigation. One major difference between
TRANSIT and GPS is. that the TRANSIT satellites are in low-
altitude polar orbits with.a 90 minute period.
Selective Availability (SA): A DoD program to control the
accuracy of pseudorange measurements, whereby the user
receives a false pseudorange which is in error by a controlled
amount. SA gives an error of approximately 100 meters.
Differential GPS techniques can reduce these effects for local
applications.
Semimajor axis: One half of the major axis of an ellipse.
SEP: Spherical Error Probable, a statistical measure of precision
defined as the 50th percentile value of the three-dimensional
position error statistics. Thus, half of the results are
within a 3D SEP value.
Session: The time period where all receivers observe the same
satellites at the same time to determine the coordinates of a
point.
Sidereal day: Time between two successive upper transits of the
vernal equinox.
Simultaneous measurements: Measurements referenced to time-frame
epochs which are either exactly equal, or else so closely
spaced in time that the time misalignment can be accommodated
by correction terms in the observation equation, rather than
by parameter estimation.
Slope distance: The three-dimensional vector distance from
station one to station two. The shortest distance (a chord)
between two points.
Slow switching channel: A switching channel with a sequencing
period which is too long to allow recovery of the integer part
of the carrier beat phase.'
Solar day: Time between two successive upper transits of the sun.
xvi
Space segment: The part of the whole GPS system that is in
space, i.e. the satellites.
Spheroid: See ellipsoid.
Spread spectrum: The received GPS signal is a wide bandwidth,
low-power signal (-l6OdBW). This property results from
modulating the L-band signal with a PRN code in order to
spread the signal energy over a bandwidth which is much
greater than the signal information bandwidth. This is done
to provide the ability to receive all satellites unambiguously
and to provide some resistance to noise and multipath.
Squaring-type channel: A GPS receiver channel which multiplies
the received signal by itself to obtain a second harmonic of
the carrier which does not contain the code modulation. Used
in so-called codeless receiver channels.
Standard positioning service (SPS): The normal civilian
positioning accuracy obtained by using the single frequency
C/A code.
State plane coordinates: A Northing (N), Easting (E) coordinate
system based on a conformal map projection that simplifies the
task of converting from latitude and longitude to a
rectangular coordinate system.
Static positioning: Location determination when the receiver's
antenna is presumed to be stationary in the earth. This
allows the use of various averaging techniques that improve
accuracy by factors of over 1000.
SV: Satellite vehicle or space vehicle.
Switching channel: A receiver channel which is sequenced through
a number of satellite signals (each from a specific satellite
and at a specific frequency) at a rate which is slower than,
and asynchronous with, the message data rate.
TDOP: Time Dilution of Precision. See DOP.
TOW: Time of week, in seconds, from midnight Sunday UTC.
xvii
Translocation: A version of relative positioning which makes use
of a known position, such as a USGS survey mark, to aid in the
accurate positioning of a desired point. Here, the position
of the mark, determined using GPS, is compared with the
accepted value. The three-dimensional differences are then
used in the calculations for the second point.
Trop: Tropospheric correction. The correction applied to the
measurement to account for tropospheric delay. This value is
obtained from the modified Hopfield model.
Troposphere: Inner layer of the atmosphere, located between 6 and
12 miles above the earth's surface.
True anomaly: The angular distance, measured in the orbital
plane from the earth's center (occupied focus) from the
perigee to the current location of the satellite (orbital
body).
Universal time: Local solar mean time at Greenwich Meridian.
Some commonly used versions of the Universal Time are:
UTO Universal Time as deduced directly from observations
of stars and the fixed numerical relationship between
Universal and Sidereal Time; 3 minutes 56.555 seconds.
UT1UTO corrected for polar motion.
UT2UTI corrected for seasonal variations in the earth's
rotation rate.
UTC: Universal Time Coordinated; uniform atomic time system kept
very close to UT2 by offsets. Maintained by the U.S. Naval
Observatory. GPS time is directly relatable to UTC. UTC -
GPS = seconds (changing constant = 5 seconds in 1988).
User interface: The way a receiver conveys information to the
person using it. The controls and displays.
User segment: The part of the whole GPS system that includes the
receivers of GPS signals.
User range accuracy (LTRA): The contribution to the range-
measurement error from an individual error source (apparent
clock and ephemeris prediction accuracies), converted into
range units, assuming that the error source is uncorrelated
with all other error sources. Values less than 10 are
preferred.
xviii
UTTM: Universal Transverse Mercator Map Projection. A special
case of the Transverse Mercator projection. Abbreviated as
the UTM Grid, it consists of 60 north-south zones, each 6
degrees wide in longitude.
VDOP: Vertical Dilution of Precision. See DOP and PDOP.
Vernal equinox: The intersection of the celestial equator with
the ecliptic, with the positive sense being from the earth to
the sun, as the sun crosses the equator from south to north.
Vertical: The line perpendicular to the geoid at any point. The
direction of the force of gravity at that point. Plumb line.
WGS-72: World Geodetic System (1972); the mathematical reference
ellipsoid previously used by GPS, having a semimajor axis of
6378.135 km and a flattening of 1/298.26
WGS-84: World Geodetic System (1984); the mathematical ellipsoid
used by GPS since January 1987. The shift from WGS-72 to WGS-
84 at our latitude (370N) is about 13.6 meters east, 45 meters
north and 2.7 meters up.
Z-count: The GPS satellite clock time at the leading edge of the
next data subframe of the transmitted GPS message (usually
expressed as an integer number of 6 seconds).
xix
APPENDIX A
CURRENT GPS APPLICATIONS IN
MINNESOTA STATE & FEDERAL
GOVERNMENT
Click HERE for graphic.
Click HERE for graphic.
APPENDIX B
ANTICIPATED GPS APPLICATIONS
IN
MINNESOTA STATE & FEDERAL
GOVERNMENT
Click HERE for graphic.
Click HERE for graphic.
Click HERE for graphic.
Click HERE for graphic.
Click HERE for graphic.
Click HERE for graphic.
Click HERE for graphic.
Click HERE for graphic.
APPENDIX C
EXISTING GPS EQUIPMENT
IN
MINNESOTA STATE & FEDERAL
GOVERNMENT
Click HERE for graphic.
APPENDIX D
GPS BASE STATIONS IN
MINNESOTA, THE FIVE
STATE REGION, AND
ACROSS THE U.S.
Click HERE for graphic.
Click HERE for graphic.
E A P E L E C T R O N I C M A I L M E S S A G E
Date: 20-Apr-1993 12:29pm EDT
From: BRENDA GROSKINSKY
(GROSKINSKY.BRENDA)
Dept: (REG,07,ESD) (E)
Tel No: 913-551-7188
See Below
Subject:Draft FGCS fixed ref. station list
Federal Geodetic Control Subcommittee
Fixed Reference Station Working Group
DRAFT REPORT 1.4
7 April 1993
ST LOCALITY ORG. CONTACT PHONE
AK Fairbanks NASA/JPL Ulf Lindqwister 818-354-1734
JPL/Allen Os Rogue
AK Petersburg FS Dave Wood 907-586-7888
Trimble CBS
AR Little Rack U. Ark Jud Rouch 501-569-8204
Ashtech L-12
AZ Prescott FS Mike Lange 602-445-1762
Trimble CBS
AZ Springerville FS M. Battin 602-333-4301
Trimble CBS
AZ Tucson FS Wallace Craig 602-670-4552
Trimble CBS
CA Barstow BLM Tim Read 619-256-2729
Trimble CBS
CA Eureka FS Larry Walter 707-442-1721
Trimble CBS
CA Goldstone NASA/JPL Ulf Lindqwister 818-354-1734
JPL/Allen Os Rogue
CA La Jolla NASA/JPL Ulf Lindqwister 818-354-1734
Ashtech P-12
CA Monterey Bestor Engr Tony Grissim 408-373-2941
Trimble 4000
ST LOCALITY ORG. CONTACT PHONE
CA Pasadena NASA/JPL Ulf Lindqwister 818-354-1734
JPL/Allen Os Rogue
CA Pinon Desert NASA/JPL Ulf Lindqwister 818-354-1734
JPL/Allen Os Rogue
CA Porterville FS Cheryl Spencer 209-784-1500
Trimble CBS
CA Sacramento FS Kevin Casey 916-551-3391
Trimble CBS
CA San Diego JCA Kurt Maynard 318-237-1300
Trimble 4000
CA San Francisco RACAL Tony Harrison 713-784-4482
Trimble 4000
CA Susanville FS Mike Jablonski 916-257-2151
Trimble CBS
CA Temucela TPC Dennis Janda 909-676-7000
Ext 373 Trimble 4000
CA Vandenberg NASA/JPL Ulf Lindqwister 818-354-1734
JPL/Allen Os Rogue
CO Inglewood GTC David Spradley 713-558-6418
Sercel NR105
CO Fort Collins FS Carl Sumpter 303-498-1749
L. Lewis Trimble CBS
CO Marcos & Mesa Verde Allen Loy 303-529-4465
Cortez Natl Park/GIS Offc Trimble Path
CO Platteville NOAA Richard Cohen 303-497-6530
Trimble Geod
DC Washington NPS Patrick Gregerson 202-619-7277
Trimble Path
ST LOCALITY ORG. CONTACT PHONE
DE Cape-Henlopen USCG Jack cash 202-267-0296
Ashtech A-12
FL Melbourne JCA Kurt Maynard 318-237-1300
Trimble 4000
FL Pensacola JCA Kurt Maynard 318-237-1300
Trimble 4000
FL Richmond NGS Miranda Chin 301-443-2520
Minimac
FL Tampa RACAL Tony Harrison 713-784-4482
Trimble 4000
GA Atlanta Fs Doug Luepke 404-347-3987
Trimble CBS
HI Kokee Park NASA/JPL Ulf Lindqwister 818-354-1734
JPL/Allan Os Rogue
IA North Liberty NASA/JPL Ulf Lidqwister 818-354-1734
JPL/Allen Os Rogue
ID Boise BLM Jeff A. Lee 208-886-2206
Trimble CBS
ID McCall FS Steve Dodds 208-634-0700
Trimble CBS
IN Bedford FS Dale Weigel 812-275-5987
Trimble CBS
IN West Lafayette Purdue B. van Gelder 317-494-2165
U. Trimble CBS
KS Kansas City EPA Brenda Groskinsky 913-551-7188
Trimble 40
KS Shawnee GTC David Spradley 713-558-6418
Sercel NR105
LA New Orleans USACE Don Schneider 504-862-1828
Trimble 4000
LA New Orleans RACAL Tony Harrison 713-784-4482
Trimble 4000
ST LOCALITY ORG. CONTACT PHONE
LA Baton Rouge USACE Don Schneider 504-862-1828
Trimble 4000
LA Lake Charles USACE Don Schneider 504-862-1828
Trimble 4000
LA Venice USACE Don Schneider 504-862-1828
Trimble 4000
LA Venice CGG Silvio Cuccerrello 713-784-0740
Sercel
MA Lexington EPA Ray Thompson 617-860-4372
Trimble 4000
MA Wesford NOS/OES Miranda Chin 301-443-2520
Minimac
MI Escanaba FS Bill Bowman 906-786-4062
Trimble CBS
MI White Fish USCG Jack Cash 202-267-0296
Point Magnavox
MN Duluth JCA Kurt Maynard 318-237-1300
Trimble 4000
MN Duluth Minn Bryce Ofstie 218-722-1972
Power Ext 2879 Trimble CBS
MN Hibbing Cliffs Ron Graeber 218-262-3461
Mining
MN Minneapolis Minn Justin Blum 612-627-5165
D.O.E. Trimble 4000
MT Butte BLM Mike Harbin 406-255-2854
Trimble Path
MT Missoula FS Don Patterson 406-329-3430
Trimble CBS
NC Fayetteville JCA Kurt Maynard 318-237-1300
Trimble 4000
NC Wilmington USACE Marc Reavis 919-251-4840
Glenn Boone Ashtech MXII
ND Bismarck NDGS Mark Luther 701-224-4109
Trimble CBS
ST LOCALITY ORG. CONTACT PHONE
NE Portsmouth USCG Jack Cash 202-267-0296
Harbor Ashtech A-12
NJ Edison EPA Mike Glowgower 908-321-6661
Trimble CBS
NJ Mt. Laurel TWT Mike Burns 609-235-7200
Trimble 4000
NJ Trenton NJDEP Lew Jacoby 609-633-1203
Trimble CBS
NM Alamogordo FS Rafael Castanon 505-437-6030
Trimble CBS
NM Pie Town NASA/JPL Ulf Lindqwister 818-354-1734
JPL/Allen Os Rogue
NM Santa Fe FS G. Burnett 505-988-6934
C. Chaves Trimble CBS
NM Silver City FS Rocky Hildebrand 505-388-8394
Trimble CBS
NS Halifax RACAL Tony Harrison 713-784-4482
Trimble 4000
NV Reno DRI Matt Chesley 702-673-7385
Astech M-12
NY Harriman Plan Mike Popoloski 914-783-8033
Dynamics Trimble 4000
Trimble Path
NY Long Island JCA Kurt Maynard 318-231-1300
Trimble 4000
NY Montauk Point USCG Jack Cash 202-267-0296
Ashtech A-12
OR Portland FS Ken Chamberlain 503-326-2921
Trimble CBS
PA State College Penn Rick Day 914-863-1615
State U. Trimble CBS
ST LOCALITY ORG. CONTACT PHONE
TN Memphis USACE Don Wilbanks 901-544-3238
Trimble 4000
TN Memphis GTC David Spradley 713-558-6418
Sercel NRLOS
TX Arlington Tex DOT Frank Howard 512-465-7452
Trimble 4000
TX Austin Tex DOT Frank Howard 512-465-7452
Trimble 4000
TX Corpus Christi Tex DOT Frank Howard 512-465-7452
Trimble 4000
TX Freeport Sercell, Lyn Weass 713-492-6688
Inc. Sercell
TX Galveston USCG Jack Cash 202-267-0296
Trimble 4000
TX Houston Tex DOT Frank Howard 512-465-7452
Trimble 4000
TX Houston JCA Kurt Maynard 318-237-1300
Trimble 4000
TX Houston GTC David Spradley 713-558-6418
Sercel NR105
TX Houston RACAL Tony Harrison 713-784-4482
Trimble 4000
TX Matagorda CGG Silvio Cuccerrello 713-784-0740
Sercel
TX Mercedes JCA Kurt Maynard 318-237-1300
Trimble 4000
TX Midland GTC Davis Spradley 713-558-6418
Sercel NR105
TX Port Aransas USCG Jack Cash 202-267-0296
Trimble 4000
TX San Antonio Tex DOT Frank Howard 512-465-7452
Trimble 4000
UT Salt Lake City BLM Robin Floor 801-539-4147
Trimble Path
ST LOCALITY ORG. CONTACT PHONE
UT Cedar City FS Steve Dodds 801-865-3700
Trimble CBS
VA Blacksburg Va Tech Paul Bolstad 703-231-5676
Trimble CBS
VA Cape Henry USCG Jack Cash 202-267-0296
Ashtech A-12
VA Corbin NOAA Leo B. Gittings 703-373-7605
Trimble 4000
WA Everett JCA Kurt Maynard 318-237-1300
Trimble 4000
WA Seattle USACE Stephen Wright 206-764-3495
Trimble 4000
WY Jackson FS Eric Winthers 307-739-5526
Trimble CBS
bbreviations
BLM U.S. Bureau of Land Management
CBS Community Base Station
CGG CGG American Services
DEP Department of Environmental Protection
DOH Department of Health
DOT Department of Transportation
DRI Desert Research Institute
EPA U.S. Environmental Protection Agency
FS U.S. Forest Service
GTC GPS Technology Corporation
JCA John Chance &.Associates
JPL Jet Propulsion Lab
NASA U.S. National Aeronautics and Space
Administration
NGS U.S. National Geodetic Survey
NOAA U.S. National Oceanic and Atmospheric
Administration
NOS U.S. National Ocean Service
NPS U.S. National Park Service
NS Nova Scotia
R/T Real Time
TPC Trans Pacific Consultants
TWT Taylor Wiseman Taylor
U. Ark University of Arkansas
USACE U.S. Army Corps of Engineers
USCG U.S. Coast Guard
Distribution:
: WILLIAM ALEXANDER (ALEXANDER.WILLIAM)
: ANDREW BATTIN (BATTIN.ANDREW)
: EARL BEAM (BEAM.EARL)
: JEFF BOOTH (BOOTH.JEFF)
: DONALD BUNDY (BUNDY.DONALD)
Use the SH option to view the entire distribution list.
APPENDIX E
OBTAINING GPS
DIFFERENTIAL DATA
IN MINNESOTA
Minnesota's DGPS public base station
the contact is: Justin Blum (612) 627-5165
. THE MINNESOTA DEPARTMENT OF HEALTH PROVIDES THIS DATA AND ITS
SERVICES AS A CONVENIENCE FOR ITS EMPLOYEES AND OTHER PUBLIC
ENTITIES. NO RESPONSIBILITY IS ASSUMED FOR DAMAGES OR OTHER
EXPENSES DUE TO THE USE OR MISUSE OF THIS DATA.
Location of the Base Station
The MDH GPS community base station is located at the Dept. of
Health building, 717 Delaware Street SE, Minneapolis. The
coordinates surveyed by MDOT are reported as:
Latitude 44ø 58' 22.04931"
Longitude 93ø 13' 39.91825"
Elevation 262.996 m HAE
Datum NAD-83
If you have any questions about these coordinates or how they were
obtained please call me or Dave Gorg at (612) 296-5710, Geodetic
Unit Supervisor, Mn/DOT.
Base Station Receiver and Data Format
The base station receiver is a Trimble Navigation Model 4000 RLII
attached to an IBM-PC compatible data logger. C/A code and L1
frequency data from all satellites in view are recorded. Data
collection is halted once per day for about 30 minutes at 06:00 UTC
(Universal Coordinated Time), 00:00 CST (midnight), for processing
and to transfer the data to the MDH network. Data are originally
stored in the Trimble DAT file format and are subsequently
processed into the SSF format. Each file contains one hour of base
station data. The DAT file contains both types of data, code and
single frequency phases, for sub-meter accuracy corrections. The
SSF file only contains code phase data for corrections with 5 meter
accuracy.
he date and time are contained in each file name. The first digit
in the SSF file has been replaced with a "&". For example,
&2111911.SSF, is the code phase data for 5:00 to 6:00 AM November
19, 1992, in the sequence: year, month, day, and hour. The DAT
file equivalent is 9211191 1. DAT. Note that the file names are
based on UTC.
SSF file name & _ _ _ _ _ _ _ .ssf
year month day hour
DAT file name & _ _ _ _ _ _ _ .dat
year month day hour
The on-line retention time for the data files is twenty days.
After that time data will be backed up on tape and will only be
available by special request. Data distribution is most easily
accomplished using Email or FTP on the internet system. The
internet address is:
justin.blum@health.state.mn.us
If you are working with GPS intermittently or just starting out,
please contact Justin (listed above) to check on the base station
condition. GPS technology is in a constant state of change and it
is never certain that the base station will be working when you
want it. GPS vendors talk about it being the next utility, but we
have a long way to go before using GPS is like turning on the
lights.
Differential Corrections
Differential corrections are the responsibility of the GPS field
data collector and are not performed at the base station. Further
data conversion (to RINEX format) required by use of other types of
GPS receivers (i.e. Magellan, Ashtech, etc.) are also the data
collector's responsibility.. SSF to RINEX format conversion
programs are available but are not guaranteed to work. Caveat
Emptor!
Other Base Stations in Minnesota
There will be additional base stations installed in Minnesota by
public and private entities. The State GPS Users Group will be
keeping track of these base stations and hopefully coordinating the
data distribution. At this time, Minnesota Power has a base
station that has been in operation since March of 1993. Cliffs
Mining Services in Hibbing has been operating a base station since
June of 1992. Also the Canadian Government has a base station
located in Thunder Bay, covering a portion of Minnesota, that has
been operational since late 1992. All of these base stations are
using the Trimble Community Base Station hardware and software.
DH Base Station Upgrade
The Mn/DOT is funded to install a base station for vehicle
tracking in the metropolitan area. As a part of this project, MDOT
has upgraded the MDH base station to single frequency carrier phase
to test sub-meter correction in the Metropolitan area. This
upgrade was just completed and the pilot test should be completed
by January, 1994.
GPS Equipment Procurement
The Base Station Workgroup is working with the Department of
Administration to write a contract with one or more GPS equipment
vendors. This would simplify the procurement process for state and
local units of government.
Files on the Internet
The base station acquires data at the rate of one reading
every five seconds. The data files are individually compressed
using PKZIP, Version 204G, to minimize disk space and transfer time
requirements. The SSF and DAT data file formats have different
sizes. One hour of SSF data is about 160 K and the equivalent DAT
file size is about 360 K. The zip compression ratio is about 50
percent. The compressed file will retain the same name but the
extension is changed to ZIP to indicate the compression type. Once
each day, the previous days data files are copied to a machine that
is accessible from the intemet. This will generally be done by
10:00 AM. We plan to keep three weeks of data available on the
intemet, if storage is available.
Internet Access to GPS Data
The gateway for intemet access is the departmental email
server, currently a Sun EPC named sunny. The intemet address for
this machine is:.
sunny.health.state.mn.us
The numeric equivalent of this address is:
156.98.80.2
The files are located under:
/public/contrib/gps/code code phase data;
/public/contrib/gps/freq single frequency carrier phase data;
/public/contrib/gps/util zip file utilities, etc.
The files are available via the intemet FTP (file transfer
protocol). If your computer is attached to intemet you should be
able to contact sunny.
TP Instructions
To Login to sunny type:
ftp sunny.mdh.umn.edu
If it works, then it will show a login screen. You should login
as:
anonymous
with the password as:
(your network address)
If this is successful then type:
cd public/contrib/gps
and then:
dir
It should show you one file and three subdirectories. The file is,
readme.txt, an updated explanation of the base station information
(this text). The three subdirectories are: code, freq, and util.
To get to the subdirectory that contains the data you need, type:
cd (subdirectory name)
Transfer the data to your location by typing the following:
binary ; this sets the type of file transfer
get --------- zip ; this transfers the file for the date and
time specified. Remember that the file
name is in the format:
& _ _ _ _ _ _ _ .ssf
year month day hour
or
& _ _ _ _ _ _ _ .dat
year month day hour
Repeat the get command for each file that you need. To back up one
level in the directory structure type:
cd .. /
The util subdirectory contains the program to decompress the files
once they've been transferred and other utilities. Transfer these
files to your computer with the following commands:
binary ; this sets the type of file transfer
mget *.* ; this transfers all files in the current
directory
When you are finished, to exit ftp type: quit
APPENDIX F
PCA PROPOSED
NOMINAL ACCURACY
STANDARDS
INTEROFFICE MEMORANDUM
Date: 03-Sep-1993 07:54 CST
From: Susan Schreifels
SCHREIFELS_S
Dept: GW Program Development
Tel No: (612) 296-8581
TO: Yuan-Ming Hsu (HSU_Y)
Subject: LDP Fact Sheet
Here is the latest version.
In the future, I will be using this document to train our division
staff regarding the LDP. It will become a standard "handout" to be
given to anyone in our division starting a new data collection
effort that is associated with locational information. It will
also be given to all section managers and unit supervisors as a
part of our data management strategic planning efforts.
In addition, we (hopefully Janet Cain's Office) will develop a
"companion" document that will identify the LDP specifications
(field size, categories, codes) to be used agency-wide. That, too,
will be given to anyone doing location associated data collection
efforts.
raft 9/2/93
Prepared by:
Ground Water and Solid Waste Division Minnesota Pollution
Control Agency
EPA's Locational Data Policy (LDP)
FACT SHEET
Introduction
In order for the federal Environmental Protection Agency (EPA) to
satisfy demand for solid environmental assessment, risk-based
decision making, and well-founded enforcement actions, EPA must be
able to perform cross-programmatic, multimedia data analyses. To
perform these functions, a common denominator among program data
collections must be developed and used as the basis for data
integration. Uniform locational information of documented quality
meets this need.
EPA's Locational Data Policy (LDP) was made effective when, after
formal EPA agency-wide review, it became an official directive
under the 2100 series and Chapter 13 of the EPA Information
Resources Management Policy Manual.
The LDP's primary purpose is to ensure the collection of accurate,
consistently-formatted, fully-documented, latitude/longitude
coordinates for facilities, sites, monitoring points, and
observation points regulated or tracked under federal environmental
programs within the jurisdiction of the U.S. EPA.
Applicability and Scope
This policy applies to all EPA organizations and agents, including
state and local government personnel, directly responsible for, or
who have delegated authority for, implementing federal
environmental laws.
Organizations with responsibilities to support EPA, including
contractors, universities, and grantees who design, develop,
compile, operate, or maintain EPA information developed for
environmental program support are required to comply with this
policy.
LDP requirements should be collected and documented as an integral
part of the following activities: permit issuance, compliance
monitoring, enforcement, reporting/notification tracking, cleanup,
environmental response and environmental monitoring.
The LDP applies to all EPA data collections that are locationally
based (i.e., data about a place), both manual -and automated. The
LDP applies to the following types of databases: inventory
databases, compliance tracking databases, activity tracking
databases, and monitoring databases. Non-locationally based data
collections, such as chemical reference systems (e.g., IRIS) or
administrative systems (e.g., IFMS), are not affected by the LDP.
The LDP may not apply for entities that are transitory (i.e., those
that change location frequently). Examples of such entities
include waste hauler, mobile air emission sources, and portable
operators. Program managers, however, may wish to capture the
boundaries of the area within which the entity moves or the
corridors along which the entity transports. Note that the LDP
does apply to permanent records maintained on places that are of
temporary environmental concerns (e.g., spill sites).
Deviations (i.e., waivers) from specific requirements of this
policy may be justified. Applications for waivers will be made to
EPA's Information Resources Management Steering Committee who will
review the applications and grant or deny such requests.
Data Requirements
The LDP requires collection of the following data elements:
* Latitude/Longitude Coordinates
* Reference Datum
* Method Used to Determine Latitude/Longitude Coordinates
(GPS recommended)
* Map Scale
* Accuracy (goal of 25 meters or better)
* Description of Entity
The LDP strongly recommends collection of the following data
elements:
* Date of Collection
* Source of Collection
Implementation of the LDP at the Minnesota Pollution Control Agency
The Minnesota Pollution Control Agency (MPCA) is currently in the
process of developing standards and conventions for the
implementation of the LDP within the MPCA. For further
information, contact the MPCA's Information Services Office.
Reference
Information for this Fact Sheet was obtained from U.S. EPA's
document entitled "Locational Data Policy Implementation Guide:
Guide to the Policy, March 1992".
LDP implementation is being coordinated for EPA by:
Jeff Booth, GIS Program Manager
Office of Information Resources Management U.S.
Environmental Protection Agency 401 M. Street SW (3405R)
Washington, D.C. 20460
Phone: (703) 235-5591
FAX: (703) 557-3186
NITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C.
JUN 11, 1993 RECEIVED
JUN 21, 1993
MPCA Ground Water
Ms. Janet Cain & Solid Waste Division
Manager, Information Systems Office
Minnesota Pollution Control Agency
520 Lafayette Road
Saint Paul, MN 55155-4194
Dear Ms. Cain:
I appreciated the recent telephone call from Susan Schreifels,
of your staff, describing progress within the Minnesota Pollution
Control Agency (NPCA) in implementing EPA's Locational Data Policy
(LDP) . Per my discussion with Susan, it is fully in accord with
the intent of the LDP for the MPCA and other state environmental
agencies to use nominal accuracy (e.g., 2 - 5 meters), rather than
absolute accuracy, as part of the metadata describing
latitude/longitude coordinates that you collect and store.
The specific programming approach Susan described also meets
the intent of the LDP. in this approach, your computer applications
would not actually store individual values in an accuracy field,
but would instead provide accuracy estimates upon request, by
referencing a lookup table of agreed-upon values, based upon the
methods by which the coordinates were obtained. It was not the
intent of the LDP to be so prescriptive that computer systems
programmers would be forced into only one coding scheme. Your
approach meets the primary goal of the LDP, which is to enable
informed secondary data usage of spatially-referenced data.
I believe that the MPCA should be commended for its efforts to
achieve consensus on a lookup table of geocoding methods and their
respective nominal accuracies. I hope that EPA program offices and
other Agency components benefit from the NPCA's experiences and
interests as they work to complete implementation of the LDP.
In order to better sustain momentum of the Agency's
implementation of the LDP, the Office of Information Resources
Management (OIRM), where I work, has decided to centralize its
support for LDP implementation. Further contacts with OIRM on this
topic should go to Jeff Booth, EPA's GIS Program Manager, in the
Program Systems Division of OIRM. Jeff can be reached at (703)
235-5591.
Steve Goranson, of EPA Region 5, would also be a good contact
person.
Thank you for your involvement in the MPCA's leadership on
this important issue.
Sincerely,
S. Hufford
Chief, Information
Management Branch
Information Management & Services Division
Office of Information Resources Management
cc: Paul Wohlleben
Daiva Baikus
Michele Zenon
Steve Schilling
Jeff Booth
Steve Goranson
Susan Schreifels
DRAFT5/25/93
Possible Nominal Accuracy Reference Table
Based on Method and Map Scale
Nominal
Accuracy Method and Map Scale
DIGITIZED
40 Feet 1:24,000
<40 Feet >1:24,000
>40 Feet <1:24,000
<10 Feet SURVEYED (Map Scale not applicable)
>500 Feet MANUAL (using any acceptable IGWIS Map Scale)
GLOBAL POSITIONING SYSTEM (Map Scale not
applicable)
<.01 Meter Survey-Quality GPS
Carrier Phase
<1 Meter Post processed differential corrected
<1 Meter Real time differential corrected
15-100 Meters Absolute mode (differentially
uncorrected)
C/A Code Receiver
2-5 Meters Post processed differential corrected
2-5 Meters Real time differential corrected
15-100 Meters Absolute mode (differentially
uncorrected)
Unknown METHOD (using any Map Scale)
.
