[Gdal-dev] Problems reading grass raster color entry

[Frank Warmerdam]

Tim Sutton wrote:
> Hi 
> >
> I am having problems reading a grass raster layer using gdal. The same routine 
> I am having problems with (see snippet below) works fine on a geotiff image. 
> I have tested the same file with gdalinfo and it seems to read the palette 
> fine. Can anyone see an obvious reason why my code is not working?
> 
> Many thanks
> 
> Tim
> 
> 
> 
>     QString colorInterp = 
> GDALGetColorInterpretationName(gdalBand->GetColorInterpretation());
>     //std::cout << "Colour Interpretation for this band is : " << colorInterp 
> << std::endl;
>     if ( colorInterp == "Palette") 
>     {
>       // print each point in scandata using color looked up in color table
>       GDALColorTable *colorTable = gdalBand->GetColorTable();
>       QImage myQImage=QImage(myLayerXDimInt,myLayerYDimInt,32);
>       myQImage.setAlphaBuffer(true);
>       for (int y = 0; y < myLayerYDimInt; y++) 
>       {
>         for (int x =0; x < myLayerXDimInt; x++) 
>         {
>           const GDALColorEntry *colorEntry = GDALGetColorEntry(colorTable, 
> scandata[y*myLayerXDimInt + x]);
>           //dont draw this point if it is no data !
>           if (myNoDataDouble != scandata[y*myLayerXDimInt + x])
>           {
>             int myRedValueInt=0; //color 1 int
>             int myGreenValueInt=0; //color 2 int
>             int myBlueValueInt=0; //color 3 int
>             //check for alternate color mappings
>             if (redBandNameQString=="Red") myRedValueInt=colorEntry->c1;
> 
> Last line fails on this : myRedValueInt=colorEntry->c1;

Tim,

I gather you are getting a crash with colorEntry being NULL? There is
no guarantee to be a color entry for every pixel value in a raster.
You need to check if GDALGetColorEntry() returns NULL.

However, I don't see any particular reason your approach shouldn't work
if all the required palette entries are available.

Best regards,

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