1. WELCOME Handouts Available Joel Cusick National Park Service Alaska Regional Office Joel_cusick@nps.gov Joel Cusick National Park Service Alaska Regional Office Joel_cusick@nps.gov Paper Presented to: ESRI Survey and GIS Summit, August 2006 Sunday, August 6, 2006 San Diego, CA Paper Presented to: ESRI Survey and GIS Summit, August 2006 Sunday, August 6, 2006 San Diego, CA

2. Are You Really Mapping Submeter? Revenge of the Shift

3. Fire Hydrant Survey Survey GPS Transform: NAD27 to WGS84_4

4. The Wrong Place 50 feet

5. Revenge of the Shift

6. NAD27-NAD83 N 61º 33’ 50.0” W 149º 44’ 21.0” NAD27 N 61º 33’ 50.0” W 149º 44’ 21.0” NAD83 200’ – 800’ horizontal

7. The Insidious Shifts 3’ – 50’ horizontal NAD83 – WGS84/ITRF00

8. Objective  Verify Datum Used in GIS  Confirm Reference Frame of GPS  Apply the Correct Transformation  Verify Datum Used in GIS  Confirm Reference Frame of GPS  Apply the Correct Transformation

9. Step 1. Verify Datum in GIS  GIS as a blender  Datum Transformations  Standardize on NAD83  Scale  GIS as a blender  Datum Transformations  Standardize on NAD83  Scale

10. GIS as a Blender  It’s the GIS Way

11. Datums and Shifts  Most all coordinate systems are referenced to a specific datum  Mix two different datums for the same point  Most all coordinate systems are referenced to a specific datum  Mix two different datums for the same point

12. Datum Shift Errors  Datum shift errors are realized when different datums are mixed and wrong assumptions are made

13. Datum Transformations  Formula to convert between two datums  Legacy GIS  Thousands  Move GPS data data to/from GIS  WGS84_To_??  Formula to convert between two datums  Legacy GIS  Thousands  Move GPS data data to/from GIS  WGS84_To_??

14. Datum Transformations  In a GIS They Work Both Ways

15. Datum Transformations  You Can’t Go Back!  Human Error is the Cause  Lack of documentation  Fundamental principle behind Mobile GIS  You Can’t Go Back!  Human Error is the Cause  Lack of documentation  Fundamental principle behind Mobile GIS

16. Standardize on NAD83  If you are using GPS data you should be in NAD83 Alaska - Part of the Continental United States since 1867! …But Still using the 1866 Spheroid

17. What’s Wrong with NAD27  Best fitting to just North America  Non Geocentric  Significant scale and azimuth distortion  Poorly determined relationship to the geoid  Best fitting to just North America  Non Geocentric  Significant scale and azimuth distortion  Poorly determined relationship to the geoid

18. Standardize on NAD83  Dave Doyle in Alaska February 2005  Cousin Vinny  Dave Doyle in Alaska February 2005  Cousin Vinny * Dave Doyle, Senior Geodesist – NGS, 2005. Alaska Survey and Mapping Conference, Anchorage Alaska.

19. Standardize on NAD83  Convert NAD27 to NAD83 using NADCON  Cases where NADCON is not a good idea  USFS reliance on PLGR’s from mid 1996 to 2000  Convert NAD27 to NAD83 using NADCON  Cases where NADCON is not a good idea  USFS reliance on PLGR’s from mid 1996 to 2000

20. Unusual NAD27 Conversion Cases * Andrew Lister, Research Forester, USDA Forest Service, 2005. email

21. – www.fs.fed.us/database/gps Mark Roper

22. Scale – Worry or Not?  GIS Data Scales  Data digitized at 1:24,000  NMAS states - +/- 40 feet  Mapping GPS Errors  Large - Autonomous GPS (pre SA)  Mid - PLGR / Autonomous GPS Today  Small - Mapping Grade  GIS Data Scales  Data digitized at 1:24,000  NMAS states - +/- 40 feet  Mapping GPS Errors  Large - Autonomous GPS (pre SA)  Mid - PLGR / Autonomous GPS Today  Small - Mapping Grade

23. Step 1. Verify Datum in GIS  Standardize on NAD83!  Convert NAD27 to NAD83 using NADCON  Special Cases Require Care  Consider Scale of Data  Standardize on NAD83!  Convert NAD27 to NAD83 using NADCON  Special Cases Require Care  Consider Scale of Data

24. I’m in NAD83 WGS84 /ITRF00 Step 2. Confirm the GPS Reference Frame  Which Reference Frame are you In?

25. Datum Adjustments  WGS84 (G1150) – most current version  “Original” NAD83 = NAD83 (1986)  NAD83 (1992)  NAD83 (2002)………….  NAD83 (CORS96) (Epoch 1997.00)  WGS84 (G1150) – most current version  “Original” NAD83 = NAD83 (1986)  NAD83 (1992)  NAD83 (2002)………….  NAD83 (CORS96) (Epoch 1997.00)

26. Over Time Datums Have Grown Apart NAD83 (1986) = WGS84 WGS84 = ITRF00 (2cm) NAD83 ~ 1 meter

27. Which Reference Frame are You In?  CORS users are in ITRF00

28. Which Reference Frame are You In?  Since you corrected against a CORS station…

29. Which Reference Frame Are You In? NAD83 (CORS96)  NDGPS (Beacon)  OMNISTAR (Satellite)  CORS Post Processed  Autonomous GPS  WAAS WGS84 (G1150) ITRF00 =

30. GPS Base Station Providers  The Trick is knowing what reference frame

31. Step 2. Confirm the GPS Reference Frame  Which Reference Frame Are You In?

32. Step 3. Apply the Correct Transformation  Use Zero Transformations when Appropriate  If NDGPS differential  NAD83 Reference Frame  If post-process CORS, WAAS – ITRF00 Reference Frame  Transform using NAD83 (CORS96)  Use Zero Transformations when Appropriate  If NDGPS differential  NAD83 Reference Frame  If post-process CORS, WAAS – ITRF00 Reference Frame  Transform using NAD83 (CORS96) See Handout for Trimble and ArcPad Users

33. Avoid the Shift  GIS Community  Surveyors  Software Developers  GIS Community  Surveyors  Software Developers

34. Avoid the Shift  GIS Community

35. Avoid the Shift  GIS Community  Test Against Control  GIS Community  Test Against Control  http://www.ngs.noaa.gov/cgi-bin/ds_radius_sf.prl

36. Avoid the Shift  Surveyors  Communicate better in map products, digital data and reference stations  Surveyors  Communicate better in map products, digital data and reference stations

37. Avoid the Shift  Software Developers  Standardize Syntax  Enhance Datum Interfaces  Software Developers  Standardize Syntax  Enhance Datum Interfaces

38. Avoid the Shift  Software Companies  Standardize Syntax  Enhance Datum Interfaces  Embed Transformation Used inside Data Layers  Software Companies  Standardize Syntax  Enhance Datum Interfaces  Embed Transformation Used inside Data Layers MXGPS www.mxgeo.com/

39. Conclusion  Verify Datum in GIS  Confirm Reference Frame  Apply the Correct Transform  Verify Datum in GIS  Confirm Reference Frame  Apply the Correct Transform

40. Acknowledgements  Carl Beyerhelm, USFS  Ron Bisio – Trimble  Shane Clarke - ESRI  Michael Dennis, Geodetic Analysis  David Doyle, NGS  Melita Kennedy, ESRI  Andrew Lister, USFS  Mark Roper, USFS  Mel Philbrook, Trimble  Myles Sutherland, ESRI  Carl Beyerhelm, USFS  Ron Bisio – Trimble  Shane Clarke - ESRI  Michael Dennis, Geodetic Analysis  David Doyle, NGS  Melita Kennedy, ESRI  Andrew Lister, USFS  Mark Roper, USFS  Mel Philbrook, Trimble  Myles Sutherland, ESRI