[gdal-dev] csharp inverse transform problem

[Gordon Paterson]

Hi everyone,

GDAL 3.5.0

I have an application written in c# that takes data in WGS84 and transforms
the coordinates to the relevant local projected CRS.

In the code I use a URN with the EPSG transformation code, for example for
ED50 data -

urn:ogc:def:coordinateOperation:EPSG::1311


to convert between EPSG:4326 and EPSG:4230 and it works great for going
from EPSG:4230 > EPSG:4326 but it doesn't give the correct results the
other way.

Checking the coordinates with gdaltransform from the command line using the
following -

gdaltransform -s_srs EPSG:4326 -t_srs EPSG:4230 -ct
urn:ogc:def:coordinateOperation:EPSG::1311


I get this -

WGS84 (EPSG:4326)
 2.25661712354279 56.4136492649363

ED50 (EPSG:4230)
2.25511244583886 56.4129769077511


which are the same coordinates I get through code, which is not right,  but
with the -i switch -

gdaltransform -s_srs EPSG:4326 -t_srs EPSG:4230 -ct
urn:ogc:def:coordinateOperation:EPSG::1311 -i


I get this -

ED50 (EPSG:4230)
2.25812179682132 56.414321584992


which is correct.

In the gdal docs there is a bReverseCT boolean parameter for
SetCoordinateOperation that is not accessible and is set to always be false
in the SWIG interface.

I set the correct Axis mapping on the spatial reference within code. I'm no
doubt missing something, what am I doing wrong?

thanks very much,

-Gordon
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