[postgis-users] Error in transforming between NAD83 and NAD27 datums

[Mark D. Andersen]

I am experiencing errors when I try to use ST_Transform to convert points from projections using NAD27 to NAD83, and vice versa.  I don't receive any errors back when I run ST_Transform, but the coordinates that are returned are incorrect.  The amount by which they are off (about 50 meters) is the amount of error I would expect with an incorrectly specified datum, so I am fairly certain that PostGIS is not transforming between NAD27 and NAD83, and vice versa.

----go from dd NAD83 to dd NAD27
SELECT ST_X(ST_TRANSFORM(ST_SETSRID(ST_MAKEPOINT(-107.074497916,42.9399159501),4267),4152)),ST_Y((ST_TRANSFORM(ST_SETSRID(ST_MAKEPOINT(-107.074497916,42.9399159501),4267),4152)));
--should return -107.073884255, 42.9399531071 (or so), but actually returns -107.074497916,42.939915951

I get the same scale of error when trying to go between UTM Zone 13 NAD83 and UTM Zone 13 NAD27 - it's basically just giving me back the same coordinates that go in, without doing the datum transformation.

SELECT Postgis_full_version() returns:

postgis_full_version
POSTGIS="2.2.1 r14555" GEOS="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.9.2, released 2012/10/08" LIBXML="2.9.1" RASTER

What am I missing?




Mark D. Andersen
Spatial Ecologist // GIS Analyst

Wyoming Natural Diversity Database<http://uwadmnweb.uwyo.edu/wyndd/>
University of Wyoming
Department 3381 // 1000 E. University Ave.
Laramie, Wyoming   82071
PHONE: 307 766 3036
FAX: 307 766 3026
EMAIL: mda at uwyo.edu<mailto:mda at uwyo.edu>

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