1 Datum Shifts Part II The Little Shift

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

3 Objective – Little Shift Test the accuracy of various GPS units Identify the NAD83-ITRF00 Shift

4 Process Export From PFO 2 “versions” of your data Assign the correct prj for ReferPT features Observe GPS Accuracy in an ArcMap dataframe relative to Survey Grade GPS Observe the on-ground relative differences between GPS in two different reference frames

5 Prior to this Presentation You occupied “Truth” Collected at least two Point Features (ReferPT) Diff. Corrected against USFS Lassen Base Station Open PFO Now

6 Export From Pathfinder Office Exported out from PFO two “versions” of the same data Once set will be BAD One set will be GOOD This was a transform, but inside Pathfinder Office

7 1: Export out as WGS84 Bad This does NOT Transform the data This is a zero transformation This Retains WGS84 or ITRF00

8 2: Export Out as NAD83 (CONUS) CORS96 Our class standard - Good Moves Data Back to NAD83 Using the Best Transform Possible

9 Datum Transform Occurred in PFO The Datum selection was switched between the 1 st and 2 nd Exports 2 nd Export was intentionally left in the reference frame of WGS84 or ITRF00 – Bad 1 st Export was done properly to line up with our GIS in NAD83– Good

10 Assign the Correct PRJ (cont) 1st Export was intentionally done wrong – Bad –Assign as UTM WGS84, Zone 10 –Name as “WGS84ReferPt” 2nd Export was done properly – Good –Assign as UTM NAD83, Zone 10 –Name Shapefile as “NAD83CORSReferPt”

11 In ArcMap Open… M:/../Data/ Exercise_Truth.mxd

12 In ArcMap Add the Poor or mis-assigned data –“WGS84ReferPt” –You get a Warning error that detects a difference –Press OK Add the Good or properly transformed shapefiles –“NAD83CORSReferPt”

13 In ArcMap Symbolize the Bad data with a Large Red Symbol Symbolize the Good data with a Large Green Symbol

14 Extra Credit The first set of data added to the data frame is being transformed into NAD83 (the datum of the data frame) using the default WGS_1984_NAD 1983_1 transform This is a “do nothing” transform Select _5 to transform the data back to NAD83 Do note, that until ArcGIS 9.2 comes out, this transform is not exact.

15 Datum Transforms thanks

16 You are here