1. GPS Accuracy Testing Using: “RTK” (Real Time Kinematic) & “One Step Transformations” (Site Calibrations)

2. GPS Accuracy Testing Procedure Results Summary and conclusions

3. Procedure

4. Found a suitable test site Established “True” positions

5. NGS 1 st Order Vertical Control 10+ Miles

6. NGS Cooperative Base Network Control Station For Horiz.

7. Measured 3 to 4 points in each area using Rapid Static

8. Set points at 1\2 Mi. increments Used new control Tied with Rapid Static

9. Transformed to North Zone Calculated one combined scale factor Converted all to LDP

10. Ran Digital Levels “True” positions established

11. Collected RTK data to compare against “true” positions

12. Set Base at north end 3 to 4 Transformation points in each area All the rest measured as topo

13. Repeated with base at the south end

14. Used: RTK WGS 84 data collected with base at north end LDP coordinates from rapid static Created the following transformations:

15. 3/4 Mile Square

16. 3/4 x 6 Mile

17. 3/4 x 10 1/2 Mile

18. Used data from base at south end 3/4 Mile Square

19. 3/4 x 5 Mile

20. 3/4 x 10 1/2 Mile

21. After comparison decided to test East- West

22. Established “True” positions in an East- West orientation Used Rapid Static GPS only for x, y, & z

23. Used primary control

24. 4 Transformation points in 3 areas Points at 1\2 Mi. increments using Rapid Static

25. Converted to LDP

26. RTK with base at West end Measured topo and transformation points

27. Repeated with RTK base at east end

28. Transformation at West end 1 Mile Square Same pattern of transformations as the North- South course

29. 1 x 5 Mile

30. 1 x 11 1/2 Mile

31. Transformation at East end 1 Mile Square

32. 1 by 6 Mile Square

33. 1 by 11 1/2 Mile Square

34. Each set of data was converted with 3 transformations Then compared to “True” Values

35. Results

42. Summary & Conclusions

43. Goal was to answer the following: Verify the accuracy of RTK. Can hard surfaces be collected with enough accuracy to pass confidence point standards? Can confidence points be collected with GPS single observation?

44. Goal was to answer the following: How are elevations affected as you go outside of a transformation (site calibration) set? How is accuracy affected by distance from the base? What is the break point?

45. What is the accuracy of RTK?  Horizontal =10mm (0.033 ft.) + 1 ppm  Vertical =20mm (0.066 ft.) + 1 ppm.  Recommends One Step Transformations less than 6 mi. sq. Leica states that 99.9% System 1200

46. What is the accuracy of RTK? One ppm for 6 mi. = 0.032 ft. Plus 0.066 ft. vertical spec. Equals 0.098 ft. 99.9% should equal or be less than 0.10 ft.

47. What is the accuracy of RTK? 180 measurements & many transformations When:  Inside transformation  0 to 3 mi. to base  GDOP less than 6  VDOP less than 4 All less than 0.10 ft.

48. What is the accuracy of RTK? When:  Inside transformation  3 to 6 mi. to base  GDOP less than 6  VDOP less than 4 4 out 0.10 ft. in height

49. What is the accuracy of RTK? Measurements exceeding 0.10 ft. Vertical Error in ft.Miles From Base 0.133.0 0.115.2 0.145.7 0.115.8

50. What is the accuracy of RTK? There will be some “Fliers”. Good conditions at test site.

51. Can hard surfaces be collected with enough accuracy to pass confidence point standards? Yes Be aware of the pitfalls

52. Can confidence points be collected with GPS single observation? Yes Single GPS observation O.K. for topo Single GPS observation O.K. for confidence points

53. How are elevations affected as you go outside of a transformation set? Elevations and Northings adversely affected Eastings to a lesser degree Affect not always immediate

54. How is accuracy affected by distance from the base? Not as well defined Inconsistent beyond 5 to 6 mi.

55. What is the break point? 5 to 6 miles from base GDOP over 6 VDOP over 4

56. What is the break point? This testing indicates 98% better than 0.10 ft. at 0 to 6 miles 0 to 5 miles from base 99.5% 0 to 3 miles 100%

57. Conclusion The following conclusions are based on the test results:

58. Conclusion Ok for Confidence Points and Hard Surfaces Distance from base and outside transformation degrades accuracy. Expect “Fliers”

59. Conclusion GDOP over 6 or VDOP over 4 will generate poor results. Keep One Step transformation size to 6 miles square or less.

60. Conclusion Stay close to the base, the closer the better within reason, no farther than 3 miles if possible. Stay within the transformation boundary as close as possible.

62. Any Questions? We’re all ears