FGCS Federal Geodetic Control Subcommittee

Test and Demonstration of the Magellan
Nav Pro 5000 GPS Receiver Sub Meter
System: July 1993

FGCS Report: FGCS-IG-94-1

November, 1994

FGCS Members:

U.S. Department of Agriculture
U.S. Department of Commerce
U.S. Department of Defense
U.S. Army Corps of Engineers
U.S. Department of Interior
U.S. Department of Transportation
Environmental Protection Agency
Federal Aviation Administration
Federal Communications Commission
International Boundary and Water Commission
International Boundary Commission
National Aeronautics and Space Administration
National Capital Planning Commission
Tennessee Valley Authority

TEST AND DEMONSTRATION OF THE
MAGELLAN NAV PRO 5000 GPS
RECEIVER SUB METER SYSTEM:
July 1993

FGCS Report: FGCS-IG-94-1

Larry Hothem
Karl Brown
Federal Geodetic Control Subcommittee

Instrument Working Group
Chair, Sally L. Frodge

For further information contact:
Secretariat, Federal Geodetic Control Subcommittee
N/CG, SSMC3, Station 8657
Coast and Geodetic Survey, NOAA
Silver Spring, Maryland 20910-3282

November 1994

For sale by the National Geodetic Information Center, NOAA, Silver Spring, MD 20910-3282

• Abstract
• Introduction
• Test Description
• Mission Planning
• Data Collection and Point Occupations
• Data Processing and Results
• Conclusion

1. Specifications Outline Magellan NAV PRO 5000 GPS Receiver
2. Test Summary Tables

• Baselines > 100,000 Meters
• Baselines > 50,000 Meters
• Baselines > 50,000 Meters
• Baselines > 100,000 Meters
• Baselines > 50,000 Meters -- 10% Outliers Removed
• Baselines > 100,000 Meters -- 10% Outliers Removed

1. FGCS test network located in the vicinity of Washington, D.C.
2. Portion of the FGCS test network near Gaithersburg, Maryland

1. Summary of Evaluation Statistics
2. Summary of Station Occupations
3. Reference Stations Collection Periods
4. Station Coordinates
5. Occupied Rover Stations
6. Baseline Data Corrected
7. Corrected Remote Location
8. Solution Error -- Meters

The Magellan NAV PRO 5000 GPS receiver system with Sub-Meter upgrade module was tested on the FGCS network in April of 1993. The test was designed to demonstrate two main points: the Sub-Meter capability of the Magellan NAV PRO, as well as the ability to successfully process accurate results using RINEX format data from a variety of reference stations ('base' station receivers).

Three Magellan receivers acquired L1 carrier phase data in a series of 45 occupations on numerous points located on the grounds of the National Institute of Standards and Technology (NIST). Magellan's post-processing software package was employed to process RINEX data collected by 3 Trimble Navigation Systems' 4000SSE reference stations, as well as 3 Ashtech LM-XII and 2 LD-XII receivers.

Please note that no least squares adjustments or other outside network adjustment programs have been applied to these coordinates. All data shown in the following tables of results were determined solely from Magellan software.

Baseline results are presented for distances ranging from 111 meters to 43.8 kilometers, with an average baseline length of 21.86 km. Total RMS error for the entire data set was 0.87 meters, within Magellan specifications of <1 meter RMS.

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The Magellan NAV PRO 5000 GPS receiver is the first hand-held system to be tested on the FGCS network of high-accuracy control points (Fig 1&2, Table 3). These points are available to GPS manufacturers as a standard for use in verifying quoted accuracy specifications, and as test platform for new GPS surveying systems. Field work and data evaluation are typically supervised by members of the FGCS to verify receiver performance, data quality, overall results, and specifications.

FGCS approval of a tested GPS system provides a qualified and independent assurance that the tested system has met or exceeded the manufacturers quoted specifications.

The NAV PRO system receives both L1 C/A Code and L1 Carrier Phase data, and will acquire at varying sampling rates from 1-second. The NAV PRO is synchronized to the GPS second, and as such may be used in certain modes against long-interval reference stations. Both C/A Code and Carrier Phase data were recorded by NAV PRO units in this test at a 1-second rate, with Sub-Meter results being derived through a proprietary algorithm using the carrier data. Full technical specifications for the NAV PRO unit are contained in Appendix A.

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The test and demonstration were conducted over the course of two periods totaling 5.5 hours on April 16, 1993 (day 106). All reference stations were requested to acquire data during the following scheduled times: Collection period 1 to begin at 1130 UTC and run until 1430 UTC, followed by period 2 beginning at 1600 UTC and ending at 1830 UTC. These times correspond to 07:30am EDT to 10:30am EDT, followed by 12:00 (noon) EDT to 14:30pm EDT. Measured vectors range from short, 111 to 1275 meters; to medium, 6 to 25 kilometers; and long, 35 to 44.9 kilometers.

Figure 1 is a general depiction of the FGCS test network, with the shortest baselines described on the attached Figure 2, a general plan of the NIST facility located in Gaithersburg, Maryland.

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Figure 1. FGCS test network located in the vicinity of Washington, D.C.

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Figure 2. Portion of the FGCS test network near Gaithersburg, Maryland

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Prior to actual field work, mission planning information was generated using the Magellan software package, as illustrated in figure 3. Information (Satellite coverage) was readily produced that showed (predicted) no trouble in finding suitable coverage during the planned test period since only 4 satellites are actually required for Magellan Sub-Meter processing. Data generated in planning sessions were used as reference during fieldwork. Planning information was based on almanac data gathered by a Magellan receiver two days prior to the actual test operation. The United States' Coast Guard GPS Bulletin Board was consulted prior to field operations to ensure sufficient satellite availability.

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A sequence of 45 field occupations occurred during the course of the overall test program. According to (as required by) Magellan specifications, each occupation was scheduled for at least 10 minutes (see Table 1). Data sets on rover test points were acquired in the static (stationary), Sub-Meter mode. Kinematic (moving point collection) operations were not performed.

Mask angles on rover units were set to 15 degrees. Data were acquired at 1-second epoch intervals for all test occupations. Data were processed for all possible tracker/rover combinations afforded by field occupations and available reference station data. (Note: Not all reference stations were able to supply full data sets as established (required) in the acquisitions schedule, see Table2).

Two NAV PRO receivers were employed as rovers to acquire data at varying times on 7 separate test stations. One NAV PRO remained stationary throughout the test sequence to act as a Magellan reference station, although these data were processed against reference station Receiver INdependent EXchange (RINEX) data as a series of remote occupations. All sessions were processed successfully through the Magellan Post Processing Software (PPSW).

Each reference station used in the test program was configured to acquire L1 Carrier Phase and C/A Code data at 1-second sampling intervals. Full specifications for each of these receivers may be obtained from their respective manufacturers. All trackers used in the program supplied data in the GPS industry standard RINEX format for use as control files in Magellan PPSW.

Data were collected by FGCS systems operators and volunteers at the National Institute of Standards and Technology, National Geodetic Survey, National Aeronautics and Space Administration, the US Corps of Engineers, the US Coast Guard, and three separate offices within the US Geologic Survey.

Field occupations were undertaken in two collection periods as described above. Weather throughout the test program was extremely inclement, with a major thunderstorm moving directly through the test network at approximately mid-morning. Some field occupations were delayed by considerable localized lightning activity and extremely heavy rainfall during the initial phases of the storm. A steady downpour and periodic lightning strikes occurred throughout the course of the second collection period. Despite the weather, 45 occupations were completed.

(Note: Inadvertent user error in the session setup during three occupations of the first collection period resulted in data sets with unacceptable Carrier Phase Dilution Of Precision (CPDOP) values. Although these four data sets were processed, CPDOP values for the results were orders of magnitude beyond Magellan specifications. These results were therefore eliminated from the final analysis as invalid data.)

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Control and remote data files were processed using broadcast ephemeris information and L1 Carrier Phase data, according to (utilizing) a proprietary Magellan algorithm for Sub-Meter results. The RINEX files supplied from the reference stations were generated using manufacturer-specific conversion programs.

Preliminary results for representative points within the survey network were determined by the end of the day, April 16. Early results were processed on a laptop 386SX/25 computer with math co-processor, while the overall analysis and final results were produced using a 486/50 desktop system. All results were processed through the menu-based Magellan software supplied with each NAV PRO receiver and Sub-Meter upgrade kit.

Table 1. Summary of Evaluation Statistics.

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The Magellan software is a simple to use program that incorporates mission planning, data transfer, file conversion, and both Code- and Carrier-Phase differential processing. A variety of common grid systems, datums, and user-definable parameters are supported in the program. Files are selected for processing through a system of windows and pick lists. Results may be output in user-selected formats such as ASCII, ArcINFO.GEN, AutoCAD.DXF, and NGS standard. Raw Magellan files may also be converted to RINEX format for processing in other manufacturers' programs.

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Tables 1 - 7 summarize the results, and provide additional reference information on baseline length, corrected remote locations, as well as Magellan-specific details such as Carrier Phase Dilution Of Precision (CPDOP) values. Full data on all occupations and corrected results are available from Magellan Systems. Baseline results are presented for distances ranging from 111 meters to 43.8 kilometers, with an average baseline length of 21.86 km. Total RMS error for the entire data set was 0.87 meters, within Magellan specifications of <1 meter RMS.

Table 2. Summary of Station Occupations

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TABLE 3. Reference station Collection Periods (UTC)

*Stations outside the requested acquisition times (1130-1430 UTC Period 1; 1600-1830 UTC Period 2)

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Table 4. Station Coordinates

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Table 5. Occupied Rover Stations

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Table 6. Baseline Data - Corrected

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Table 7. Corrected Remote Location

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Table 8. Solution Error - Meters

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The following is a brief specifications description of the Magellan Systems' NAV 5000 NAV PRO Handheld GPS Receiver, including basic data on available accuracies, dimensions, operating characteristics and other pertinent information.

OPERATIONAL CHARACTERISTICS

General: 5-Channel GPS receiver;
differentially correctable internal storage buffer with namable waypoints.
Update Rate: User-selected, from 1 to 999 seconds
Sampled data: L1 C/A Code, L1 Carrier Phase
Time to first fix: Typically less than 35 seconds
Almanac collection: Typically 12.5 minutes
Accuracy*: Single-fix - 15 meters RMS in 2D or 3D mode
Averaging - 12 meters RMS in 2D or 3D mode
Differential -
3 meters RMS horizontal
5 meters RMS spherical
<1 meter RMS spherical with Sub-Meter Module
Operating Life: 10 hours with AA alkaline batteries (6) 4 hours with rechargeable NiCad Continuous with external power

PHYSICAL CHARACTERISTICS

Size: 8.75" x 3.50" x 2.13" excluding antenna
Weight: 30 ounces with batteries
Specific Gravity: 0.8 (it floats)
Display : 4-line, 16-character, lighted alphanumeric LCD
Operating Temp.: -10 to 60 degrees Centigrade Storage
Temp.: -40 to 70 degrees Centigrade
Casing: 1 Completely sealed waterproof, dustproof, and shock resistant with integrated keypad

*Please note accuracies as quoted are specified for a non-Selective Availability environment. SA accuracies are specified by the US DoD to be within 100 meters RMS 95% of the time, and within 300 meters RMS 99.99% of the time.

The Magellan Post-Processing software (packaged with each unit) features such menu-driven functions as: mission planning; the ability to log data directly and download stored files; conduct statistical analyses on data files; convert data products to a variety of GIS formats, as well as interface with other types of GPS systems through the RINEX format standard; and perform differential corrections for increased accuracy.

Each Magellan NAV 5000 NAV PRO unit may be configured in the field with datum and projections to match the specifications of the host GIS program. Data as collected is then automatically georeferenced to the host system for simple and straightforward GIS updates and input. Magellan units may be used as stand-alone receivers for rough position data gathering, or may be used in tandem for differential work.

GENERAL INFORMATION

- The 5000 NAV PRO uses an integrated quadrafilar antenna for straightforward field operations and ready access to position fixes in difficult canopy situations. The MultiPath-Resistant microstrip antenna is typically used with the 5000 NAV PRO when working in the Sub-Meter mode, and provides the "clean" signal quality necessary for high-accuracy applications.

- The 5000 NAV PRO will provide a variety of accuracy levels when used in the differential mode. Accuracy levels vary according to the method in which and which type of data are gathered, ranging from 10 meters in the most basic "field differential" mode to <1 meter using the sophisticated Sub-Meter program.

- Meter-level position fixes are obtained with 3-5 minutes of occupation time on a field point; the Sub-Meter results require a 10 minute occupation of the remote point. Meter-level remote operations may be conducted as far as 400 kilometers from the control point; Sub-Meter operations must be conducted within 50 kilometers of the benchmark.

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