[gdal-dev] csharp inverse transform problem

[Even Rouault]

Gordon,

urn:ogc:def:coordinateOperation:EPSG::1311 is from ED50 to WGS84, so 
what you observe with gdaltransform is expected. You'd get the correct 
result by just switching EPSG:4326 and EPSG:4230

Regarding the use of the API, it is true that this was lacking. Adressed 
per https://github.com/OSGeo/gdal/pull/6175

Even

Le 09/08/2022 à 13:16, Gordon Paterson a écrit :
> 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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