[gdal-dev] OGR projections - towgs84 issue

[Steve Riddell]

When trying to transform a projected coordinate (UTM 14) from WGS84 to
NAD83, using the  OGRCoordinateTransformation class, my transformed output
point exactly matches my input point, even though I have specified valid,
non-zero +towgs84 parameters for the NAD83 coordinate system.

 

If I do the same task directly using cs2cs, I get the expected ~2 meter
shift.

 

Using cs2cs:

cs2cs +proj=utm +zone=14 +ellps=WGS84 +datum=WGS84 +units=m 

  +to +proj=utm +zone=14 +ellps=GRS80 +datum=NAD83 +units=m
+towgs84=0.9910,-1.9072,-0.5129,0.0258,0.0097,0.0117,0.0000

 

Input -> 500000 3500000 100

Output-> 499998.20       3500002.08 98.80

 

Using GDAL (C#):

.

SpatialReference src = new SpatialReference("");

src.ImportFromProj4("+proj=utm +zone=14 + ellps=WGS84 +datum=WGS84
+units=m");

SpatialReference dst = new SpatialReference("");

dst.ImportFromProj4("+proj=utm +zone=14 + ellps=GRS80 +datum=NAD83 +units=m
+towgs84=0.9910,-1.9072,-0.5129,0.0258,0.0097,0.0117,0.0000");

CoordinateTransformation ct = new CoordinateTransformation(src, dst);

double[] p = new double[3] { 500000, 3500000, 100 };

ct.TransformPoint(p);

Console.WriteLine("x:" + p[0] + " y:" + p[1] + " z:" + p[2]);

 

Output-> x:500000 y:3499999.99990104 z:100

 

 

It appears that the towgs84 parameters were ignored, resulting in WGS84 and
NAD83 being treated as identical. I'm new to using GDAL, so perhaps I'm
missing something? Any help appeciated.

 

Thanks,

Steve

 

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