Performance Assessment of a GPS Network RTK Service

1. Performance Assessment of a GPS Network RTK Service J. Aponte, X. Meng, A. Dodson, T. Moore, C. Hill IESSG, The University of Nottingham, UK M. Burbidge Leica Geosystems (UK) Performance Assessment of a GPS Network RTK Service

2. Content • Objectives • Leica SmartNet • Methodology • Quality Measures • Accuracy and Precision • Availability • Integrity • Repeatability • DOP • Conclusions • Future Work • Acknowledgements Performance Assessment of a GPS Network RTK Service

3. Objectives • Assess performance of SmartNet service from end user’s point of view, based on: • Accuracy • Precision • Integrity • Availability • Repeatability • Number of satellites and DOP Performance Assessment of a GPS Network RTK Service

4. Network RTK GPS Service: Leica SmartNet NRTK GPS service for Great Britain and Ireland: • Partnership: Leica Geosystems and OSGB, OSI, and OSNI • 142 RS • 16 RSs in Ireland. • 20 Leica RSs (8 GPS/GLONASS RSs). • Operational from January 2006 in GB and July 2007 in Ireland. • GPS receivers supporting RTCM formats 2.3/3.1 • Leica SpiderNet • RSs: Leica 500/1200 receivers and Chokering Antennas. Performance Assessment of a GPS Network RTK Service

5. AT502 DF Antenna Antenna Signal Splitter RTCM 3.1 corrections received via GPRS Leica Geosystems SR-530 GPS Receiver Leica Geosystems GX-1200 GPS Receiver Raw data logged in Receiver’s Memory Card for Post-processing Raw data logged in Receiver’s Memory Card for Post-processing Real Time NRTK solution saved in a Laptop for analysis (NMEA GGA format) Assessment Methodology • Static Tests: accuracy, precision, availability, integrity and repeatability • Kinematic Tests: accuracy, availability and integrity • TK1 covered a built-up area • Influence number of GPS satellites and their geometry, age of the NRTK corrections (AoC) Equipment Configuration • NRTK Service tested “as it is” Performance Assessment of a GPS Network RTK Service

6. Assessment Methodology Static Tests Kinematic Tests Performance Assessment of a GPS Network RTK Service

7. Quality Measures:Accuracy and Precision Accuracy (error), how far the coordinates observed during testing were from the true values. Precision, degree of closeness that repeated measurements displayed (Standard Deviation of the observations, 1 Sigma, about 68% of observations). Accuracy and Precision Obtained during both Static and Kinematic Tests (NRTK Epochs). Accuracy averages: 0.70 to 1.27 cm Easting 5.22 to 3.08 cm Northing 4.55 to 3.23 cm Height Precision averages: +/- 5.41 to 0.97 cm East +/- 7.37 to 1.34 cm North +/- 12.67 to 2.58 cm Height Performance Assessment of a GPS Network RTK Service

8. Quality Measures:Accuracy and Precision ENH Errors during TS4.1 All Epochs NRTK Epochs Performance Assessment of a GPS Network RTK Service

9. Quality Measures:Accuracy and Precision Percentage of Observations with Accuracy better or worst than 5 cm. Static Tests Kinematic Tests Performance Assessment of a GPS Network RTK Service

10. Quality Measures:Availability Availability, percentage of observations in which a NRTK solution (integer ambiguities resolved) was obtained Detailed percentage of observations performed under the different solution types during tests. NRTK Availability results Performance Assessment of a GPS Network RTK Service

11. 0 – 1 cm 1 – 5 cm >5 cm Quality Measures:Availability TK1 2D RMSE Errors as Observed in the Covered Route Factors Affecting the Availability during the Kinematic Tests All Epochs NRTK Epochs Performance Assessment of a GPS Network RTK Service

12. Quality Measures: Integrity Integrity, percentage of NRTK observations with accuracy better than 5 cm. Percentage of observations with errors better than 5 cm (Integrity). ENH Errors during TS4.2 (NRTK Epochs). Performance Assessment of a GPS Network RTK Service

13. Quality Measures: Repeatability Repeatability, similarity between the errors obtained during two different tests carried out under similar conditions (NRTK Epochs) Repeatability between TS5.1 (Light Colour) and TS5.2 (Dark Colour). 8233 common epochs of a total of 10800 epochs. Repeatabilitybetween TS4.1 (Light Colour) and TS4.2 (Dark Colour). 4331 common epochs of a total of 6600 epochs. Performance Assessment of a GPS Network RTK Service

14. Positioning Quality ResultsN. SVs in view and DOP Influence of N. SVs in view and their geometry over the positioning solution Influence of the HDOP over the Errors during TS4.2 (All Epochs). Influence of the Number of GPS satellites in View over the Errors during TS4.2 (All Epochs). Performance Assessment of a GPS Network RTK Service

15. Conclusions • SmartNet offers high centimetric accuracy (1.27 cm Easting, 3.08 cm Northing and 3.23 cm Height) for tests. • It also achieves high precision (1-sigma) (+/- 0.97 cm East, +/-1.34 cm North and +/- 2.58 cm Height). • Availability of the NRTK solution is the main drawback. Centimetric accuracy and precision only achieved during about 90% of the time in static tests and 58% during the kinematic tests. • Lack of availability mainly due to external factors and not directly related to the NRTK systems: • GPS signal disturbances (blockage). • Low number of GPS satellites in view and bad DOP. • Interruptions of the GPRS communication link. Performance Assessment of a GPS Network RTK Service

16. Current and Future Work • Investigating the impact of different commercial GSM/GPRS wireless services over the NRTK GPS availability. • Examining the performance of the different NRTK concepts such as VRS and MAC. • Study and development of NRTK GPS quality measures for service providers and final users. Performance Assessment of a GPS Network RTK Service

17. Acknowledgements • UK’s Engineering & Physical Sciences Research Council (EPSRC) for partially funding this project to the first author through its MTP scheme at the University of Nottingham. • Special thanks to Leica Geosystems (UK) for providing, free of charge, the SmartNet connection used during this research. • PhD studentship to the first author is jointly awarded by the EPSRC under its CASE PhD Studentship scheme and Leica Geosystems (UK). Performance Assessment of a GPS Network RTK Service

18. Performance Assessment of a GPS Network RTK Service J. Aponte, X. Meng, A. Dodson, T. Moore, C. Hill IESSG, The University of Nottingham, UK M. Burbidge Leica Geosystems (UK) Performance Assessment of a GPS Network RTK Service