Datums & Coordinate Systems

1. Datums & Coordinate Systems Revenge of the Shift NAD27 Datum

2. Objective • Identify different datums • Identify different coordinate systems

3. Setting The Stage • GPS is rigid – collects one way • GIS is flexible – designed to share • #1 reason GPS data doesn’t line up in GIS - coordinate system/datum mismatch • How do we fix it? – Educate

4. Coordinate Systems • Latitude and Longitude • Universal Transverse Mercator (UTM)

5. 90°N Parallels of latitude north latitude 0° latitude equator south latitude Lat / Long Coordinate SystemLatitude

6. 0° longitude Prime Meridian Meridians of longitude West Longitude Lat / Long Coordinate SystemLongitude Grenwich, England East longitude

7. UTM Coordinate Systems A plane coordinate system to relate the coordinates of points on earth’s curved surface with the coordinates of the same points on a plane or flat surface Allows projection of a spherical surface onto a flat surface

8. 180 174 168 162 156 150 144 138 132 126 120 114 108 102 96 90 84 78 72 66 60 54 48 UTM Zones in North America

9. “Figure” of the Earth Best-fit ellipsoid (e.g., GRS-80, WGS-84)

10. Datum and Ellipsoids • Datum - represented by ellipsoid • Reference ellipsoid examples: • Clarke 1866 • GRS 80 • WGS 84

11. Common Geographic Datums • NAD27 • NAD83 • WGS84 • ITRF00

12. NAD27: Clarke 1866 ellipsoid origin in Kansas Datum Origin on Surface of Earth Ellipsoid Model based on less precise surveys

13. NAD27: Leaving Behind • Invented Space Travel • Increasing accuracy of surveys • Shift from optical surveys to a mathematical model of the Earths shape • The result is a specific point on the landscape can take on multiple meanings

14. GPS Datum: WGS 84 • Origin is at the Earth’s center of mass (geocentric) • This is the datum used for the NAVSTAR GPS satellites

15. WGS84: WGS84 ellipsoid origin center of earth The origins of the WGS84 and NAD83 ellipsoids are at the center of the earth’s mass, which makes them ideal for a GPS datum

16. Datum Adjustments • Known as Datum Adjustments or Epochs • WGS84 (G1150) – most current version • “Original” NAD83 = NAD83 (1986) • NAD83 (1992) • NAD83 (2002) • …… • Most Current NAD83 • NAD83 (CORS96) (Epoch 2003.00)

17. Over Time Datums Have Grown Apart NAD83 NAD83 = WGS84 WGS84 ~4+ feet

18. Differences between Datums NAD27 ≠ NAD83 (1986) 33 to 700 feet NAD27 Datum

19. Shift Happens - Redmond OR 2005 Example 710 Feet

20. Differences between Datums • WGS84 = ITRF00 about 2cm • NAD83 (CORS96) ≠WGS84 about 4.3 feet For Arcata

21. Reference Frames • Differentially corrected GPS data are always in terms of the corrections source’s reference frame. • In Arcata we are using CORS station data and therefore must apply the correct datum transform between the GPS data and your GIS

22. Mapping / Coordinate System • For Arcata BLM Office in Pathfinder Office Coordinate System:UTM Zone 10N Datum: NAD 83 (CONUS) CORS96 Accuracy Test on Friday

23. Reason Were Using NAD83 (CONUS) CORS96 GIS In NAD83 Using CORS96 CORS ITRF00 ~4+ feet

24. When Do Datums/Coordinate Systems Matter? • PFO Map View • Coordinate system • Terrasync • Coordinate System • Export Utility • Shape Export Coordinate System • ArcGIS Catalog • Define Projection • ArcGIS • Data Frame Properties – Coordinate System Tab

25. GPS Datum Tips • Summary: • Check, check, check • ASK your GIS Specialist • Good handouts in <cd>/references

26. Conclusion • Now that you’ve learned there are differences it will be important that you learn how to… • Make it Match • Pre-Field Day 2 • Datum Transforms • Friday’s Test against Truth

27. You are here

31. Matching Datums Revenge of the Shift I’m using WGS84 I use GPS for all my mapping. I’m using NAD83(1986) 4.3 ft

32. Objective • Overview of Matching Datums and Coordinate Systems in Pathfinder Office and Data Transfer

33. Taking “GIS” out in the Field • Rasters • Vectors • All require a projection (coordinate system) defined ahead of time

34. Matching Data Steps • Know what it is – Metadata helps • Tell Pathfinder Office the correct Datum and Coordinate System

35. When Do Datums/Coordinate Systems Matter? • PFO Map View • Coordinate system • Terrasync • Coordinate System • Export Utility • Shape Export Coordinate System • ArcGIS Catalog • Define Projection • ArcGIS • Data Frame Properties – Coordinate System Tab

36. Today’s Background Image • Humboldt Campus Map • PDF obtained from Website • Converted to TIFF • Co-registered 12 control points between Ortho • ~ Depending on accuracy of Ortho, maybe +/- 20 meters in horizontal accuracy

37. Coordinate Systemand Datum Coordinate System:UTM Zone 10N Datum: NAD 83 (CONUS)

38. Next Step • Data Transfer background imagery to the GeoCE device

39. You are here

43. Datum Transforms Getting it Right in Pathfinder Office

44. Objective • Identify the proper reference frame for different differential sources • Learn how to apply the correct datum transformation inside PFO

45. Prior to this Presentation • You occupied “Truth” • Collected at least one Point feature • Now we can compare!

46. Mapping Grade GPS Accuracy • Verification of accuracy is essential to gain confidence • We have to ensure we transform the data correctly to GIS

47. Accuracy Slides Using Real Data.

48. Today is Your Chance to Test • First Some Background

49. NAD83 Developed Using WGS84 Review The origins of the WGS84 and NAD83 ellipsoids are at the center of the earth’s mass, which makes them ideal for a GPS datum

50. Over Time Datums Have Grown Apart Review NAD83 NAD83 = WGS84 WGS84 ~4+ feet