1. Beginning Basic step-by-step demonstration for: Obtaining Basefile from CORS or local GPS web sites Using basefiles for Differential Correction of Trimble Rover files (.ssf) using Pathfinder Office

2. overview Differential correction compares and corrects your Rover file using a Base file, from a stationary base station receiver (at a known location) for the exact same time as your Rover file. The first step is to obtain a base file. The most common source are CORS web sites. Even though we may not use a CORS site, it is important to be familiar with the CORS format…

3. 4 CORS home

4. 5 CORS data

5. 6 CORS selected

6. Use skagit instead HOWEVER: For local GPS work (within Whatcom County), the Skagit County GPS base station is supperior: Closer 5 second sampling interval (Whidbey CORS is 30 second) So… use their site instead

7. 7 skagit cors

8. 8 skagit ssf

9. 9 skagit ssf list

10. 10 skagit ssf select

11. 11 skagit download

12. 12 c:/pfdata

13. 13 pfdata/default

14. 14 File open

15. 15 zip file Double click to open

16. 16 extract

17. 17 extract to base Extract to C:/Pfdata/default/base folder

18. 18 base file Base file in Base folder…

19. Pathfinder Now, having downloaded a base file for the correct time period, a Rover file can be corrected using Pathfinder office…

20. 1 Windows Open Pathfinder office

21. 2 Start Pathfinder

22. 3 Default

23. 19 Pathfinder Add your GPS data

24. 19 Opened file

25. 19 open Rover file Open Uncorrected Rover file in Pathfinder

26. 19 Opened file Uncorrected Rover file

27. 20 Util Differentially correct your Rover file using the corresponding base file

28. 21 diff correction

29. wait Wait for the Differential Correction window to open … for some reason this seems to take a few minutes.

30. 22 Local search

31. 22 Local search in base

32. 23 matching files

33. 24 base data ok

34. 25 smart code ok Use Smart Code and Carrier Phase Processing

35. 26 diff cor done

36. 27 open files Compare corrected and uncorrected files

37. 28 Open both files Open both original Uncorrected rover file And corrected file for comparison.

38. 29 zoom Drag a box with zoom tool

39. 30 close up of both Compare the two files…

40. Export ‘em Both the uncorrected Rover file and the corrected file can be exported to ArcView shapefiles for GIS use and spatial analysis… (see GPS_PF-AV_demo.ppt…)

41. fini