[gdal-dev] RPC transform

[Frank Warmerdam]

Yehiyam,

I do not see why you think the AREA_OR_POINT value ought to have any
influence on how DEM values are interpolated.

Note that a PixelIsPoint GeoTIFF file will already result in a GDAL
GeoTransform that is offset by half a pixel.  The GDAL GeoTransform always
treats pixels as areas, and GDAL interpolators - presumably including the
for RPCs - should treat the pixel value as being at the center of the pixel
area for the purpose of interpolation (regardless of whether that value is
point or area).

On the other hand, I am denying the possibility that the RPC DEM
interpolation is always off by half a pixel.  I haven't actually looked
closely at that code lately and the RPC code is not so very well tested and
validated.

Best regards,
Frank


On Wed, Jan 16, 2013 at 4:40 AM, Livneh Yehiyam <yehil at rafael.co.il> wrote:

>  Hi****
>
> I have a question about the RPC transform implemented in gdal_rpc.cpp.****
>
> If a dem file is specified in the transform options (RPC_DEM) the file is
> sampled to retrieve the elevation of the transformed point.****
>
> In the case where the dem file is a DTED file (which defines AREA_OR_POINT
> to POINT), shouldn't the pixel/line values in the dem file be offset by
> half a pixel to get the correct height?****
>
> ** **
>
> Thanks****
>
> Yehiyam****
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