1 datum shifts part ii the little shift. 2 matching datums revenge of the shift i use gps for all my...
TRANSCRIPT
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Datum Datum Shifts Part IIShifts Part II
The Little Shift
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Matching Matching DatumsDatums
Revenge of the Shift
I use GPS for all my
mapping. I’m using
NAD83(1986)
I’m using WGS84
4.3 ft
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Objective – Little ShiftObjective – Little Shift
• Test the accuracy of various GPS units
• Identify the NAD83-ITRF00 Shift
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ProcessProcess
• 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
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Prior to this PresentationPrior to this Presentation
• You occupied “Truth”
• Collected at least two Point Features (ReferPT)
• Diff. Corrected against USFS Lassen Base Station
• Open PFO Now
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Export From Pathfinder OfficeExport 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
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1: Export out as WGS841: Export out as WGS84
• Bad This does NOT Transform the data
• This is a zero transformation
This Retains
WGS84 or ITRF00
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2: Export Out as NAD83 (CONUS) 2: Export Out as NAD83 (CONUS) CORS96CORS96
• Our class standard - Good
Moves Data Back to NAD83 Using the
Best Transform Possible
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Datum Transform Occurred in Datum Transform Occurred in PFOPFO
• The Datum selection was switched between the 1st and 2nd Exports
• 2nd Export was intentionally left in the reference frame of WGS84 or ITRF00 – Bad
• 1st Export was done properly to line up with our GIS in NAD83– Good
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Assign the Correct PRJ (cont)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”
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In ArcMapIn ArcMap• Open… M:/../Data/ Exercise_Truth.mxd
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In ArcMapIn 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”
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In ArcMapIn ArcMap• Symbolize
the Bad data with a Large Red Symbol
• Symbolize the Good data with a Large Green Symbol
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Extra CreditExtra 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.
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Datum Datum TransformsTransforms
thanks
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