[Proj] NGS Control Points
robert at dgi.com
Tue Jun 21 11:45:12 EST 2011
I have noticed that control points from the National Geodetic Survey (USA)
NAD83 to NAD27 transform values do not agree with transforms done using BM.
I have applied the 1983 to 1927 shift values provided in the data sheets and
compared these to an actual transform run. The transform shows a
for instance for point HT0774, of a small amount.
Data sheet (NAD83): 37.77092832 N -122.39812240
Data sheet (NAD27): 37.77098056 N -122.39707500
Transform 83 to 27: 37.77099882 N -122.39704051
Are these differences so small that one need not worry? If I calculated this
correctly the difference is around 3.5 feet for the latitude. I'm not a
geodecist and realize that the process is not absolute.
Why the difference?
Dynamic Graphics, Inc.
Alameda, CA. USA
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