[gdal-dev] Maps with GCP in C#

[Tamas Szekeres]

Patrik,

You could do something like:

GCP[] GCPs = dataset.GetGCPs();
double[] adfGeoTransform= new double[6];
Gdal.GCPsToGeoTransform(GCPs, adfGeoTransform, 0);

// apply the transformation
dfGeoX = adfGeoTransform[0] + adfGeoTransform[1] * X + adfGeoTransform[2] *
Y;
dfGeoY = adfGeoTransform[3] + adfGeoTransform[4] * X + adfGeoTransform[5] *
Y;

// calculate the inverse (handling det=0 would also be required)
double det = adfGeoTransform[1] * adfGeoTransform[5] - adfGeoTransform[2] *
adfGeoTransform[4];
X = ((dfGeoX - adfGeoTransform[0]) * adfGeoTransform[5] - (dfGeoY -
adfGeoTransform[3]) * adfGeoTransform[2]) / det;
X = ((dfGeoY - adfGeoTransform[3]) * adfGeoTransform[1] - (dfGeoX -
adfGeoTransform[0]) * adfGeoTransform[4]) / det;

BTW: I recall I already have an open ticket to add these functions (by
exposing GDALApplyGeoTransform and GDALInvGeoTransform would be sufficient)
in the SWIG interface
http://trac.osgeo.org/gdal/ticket/1531


Best regards,

Tamas



2009/6/27 patsv <patsv at bredband.net>

>  Hi, all this is my first post to this list.
>
> I am fiddling with some gps data that I want to plot onto a .BSB chart.
>
> I think I have understood howto project the gps data to geo-coordinates
> with the spatialreference and transformpoints.
>
>  And then it seems possible to translate from screen to geo-coordinates
> with   GCPToGeoTransform.
>
> But how to do the inverse geo-coordinate to screen with GCP.
>
> It seems that the GDALCreateGCPTransformer and GDALGCPTransform can do
> both.
>
> But I cannot find the support in C# or is it hidden in some class?
>
>
>
> Regards
>
> Patrik Svensson
>
>
>
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> gdal-dev at lists.osgeo.org
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