Hi all Thanks for your answers
Just to get some values, the VRT was enough to get an idea. Thanks Jukka. The questions was more like "this should be somewhere, and I do not find it", but apparently "it was not there". I see that GDALRasterInterpolateAtPoint could be useful (I am surprised it was was not needed before). I will try to add it at some point. Best regards, Javier. On Wed, 24 Apr 2024 at 15:16, Even Rouault <even.roua...@spatialys.com> wrote: > > Le 24/04/2024 à 15:00, Michael Sumner a écrit : > > Or a grouping function that returned the cell index for neighbours and > weighting that are involved in whatever calculation summary is wanted. > > That doesn't seem super user friendly, as users would still be left to do > the raster value extraction and applying the weights, taking into account > nodata, etc. Not trivial. What is the advantage of this compared to > returning the interpolated value? The only one I see is to potentially save > a bit of computation if you need to interpolate values at the same location > in multiple bands, but the performance gain would probably be marginal (or > if not, then a variant of the function dealing with multiple bands could be > offered) > > > Maybe the warper could return this as a starting point rather than doing > the "task at hand". ? > > The warper code has indeed a "FilterFuncType > GWKGetFilterFunc(GDALResampleAlg eResampleAlg)" method that returns a > function that returns interpolation weights and int > GWKGetFilterRadius(GDALResampleAlg eResampleAlg). The code in > GDALRPCGetDEMHeight() has an interesting logic where it caches a window of > interest around the first queried pixel so that subsequent queries in the > neighbouroud can be honoured without going to RasterIO(). This > substantially improves performance in the RPC case, in particular during > reverse transformation where you use an iterative method and thus may need > a lot of DEM extraction to compute a single point. > > > > > On Wed, Apr 24, 2024 at 8:51 PM Even Rouault via gdal-dev < > gdal-dev@lists.osgeo.org> wrote: > >> Hi, >> >> I guess this discussion, and past similar ones, calls for an enhancement. >> A new API function, like CPLErr >> GDALRasterInterpolateAtPoint(GDALRasterBandH, double dfPixel, double >> dfLocation, GDALRIOResampleAlg eInterpolation, double *pdfValue), that >> could be used by a new mode of gdallocationinfo. The GDALRPCGetDEMHeight() >> function in alg/gdal_rpc.cpp is a plausible candidate implementation for >> bilinear and bicubic (we could potentially restrict to that at the moment). >> >> Even >> Le 24/04/2024 à 10:33, Javier Jimenez Shaw via gdal-dev a écrit : >> >> Hi >> >> I would like to read in QGIS or GDAL an interpolated value in a DSM >> (well, actually it is a geoid model, but it is the same behaviour). See >> that I do not want the pixel value, but the linear interpolation among the >> neighbour pixels, assuming that the pixel value is in the center of the >> pixel. >> For instance, this file >> https://www.isgeoid.polimi.it/Geoid/Asia/Japan/japan2000_g.html >> >> Is there any way to get it (without implementing the interpolation >> myself)? >> If I understood correctly gdallocationinfo is not interpolating, just >> giving the pixel value. >> >> Thanks >> >> .___ ._ ..._ .. . ._. .___ .. __ . _. . __.. ... .... ._ .__ >> >> _______________________________________________ >> gdal-dev mailing >> listgdal-dev@lists.osgeo.orghttps://lists.osgeo.org/mailman/listinfo/gdal-dev >> >> -- http://www.spatialys.com >> My software is free, but my time generally not. >> >> _______________________________________________ >> gdal-dev mailing list >> gdal-dev@lists.osgeo.org >> https://lists.osgeo.org/mailman/listinfo/gdal-dev >> > > > -- > Michael Sumner > Software and Database Engineer > Australian Antarctic Division > Hobart, Australia > e-mail: mdsum...@gmail.com > > -- http://www.spatialys.com > My software is free, but my time generally not. > >
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