[gdal-dev] RPC transform

[Dmitriy Baryshnikov]

Hi Frank,

I only want to note that the default is bilinear interpolation of the DEM.

Part of the code: const char *pszDEMInterpolation = 
CSLFetchNameValueDef( papszOptions, "RPC_DEMINTERPOLATION", "bilinear" );

Best regards,
     Dmitriy

16.01.2013 22:47, 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 
> <mailto: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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