Le mercredi 20 janvier 2016 08:26:51, trewdbal a écrit :
> Hi Folks,
>
> I'm trying to read an image using ReadBlock, but the array is not filled
> with raster values.
> It works with RasterIO.
>
> The code below is copied from the GDAL doc ( page
> <http://www.gdal.org/classGDALRasterBand.html#ad80cecc562fd48f5783677de6253
> 60ac> ), I just change the type of the pabyData array (I need float32).
> I tested with several raster formats, without result.
You can only use a destination array of Float32 if the natural data type
reported by GetDataType() is GDT_Float32. IReadBlock() has no way to know the
data type you expect.
If you need to read in a particular data type, which is not necessarily the
natural data type of the band, you must use RasterIO(GF_Read, ... ,
GDT_Float32, ....) instead
>
> Another point, maybe linked with the previous, in the doc at the line :
> GByte *pabyData = (GByte *) CPLMalloc(nXBlockSize * nYBlockSize);
> I'm confused not reading
> GByte *pabyData = (GByte *) CPLMalloc(nXBlockSize * nYBlockSize *
> sizeof(GByte));
sizeof(GByte) == sizeof(unsigned char) == 1 per the C standard
>
> Thanks for any help.
> Trewdbal
>
> int main()
> {
> std::cout.precision(12);
>
> GDALAllRegister();
> const char* PANFile = "/home/ficus/Code/Covariance/rasters/pan2048.tif";
>
> GDALDataset *poDataset;
> poDataset = (GDALDataset *) GDALOpen( PANFile, GA_ReadOnly );
>
> GDALRasterBand *poBand;
> int nXBlockSize, nYBlockSize;
>
> poBand = poDataset->GetRasterBand( 1 );
> poBand->GetBlockSize( &nXBlockSize, &nYBlockSize );
>
> unsigned int SIZEX = poBand->GetXSize();
> unsigned int SIZEY = poBand->GetYSize();
>
> int nXBlocks = (SIZEX + nXBlockSize - 1) / nXBlockSize;
> int nYBlocks = (SIZEY + nYBlockSize - 1) / nYBlockSize;
>
> std::cout << " NBlocks = " << nXBlocks << " " << nYBlocks << std::endl;
> std::cout << " Block Size = " << nXBlockSize << " " << nYBlockSize <<
> std::endl;
>
> float* pabyData = (float*)malloc(nXBlockSize * nYBlockSize *
> sizeof(float));
>
> int nXValid = 0;
> int nYValid = 0;
>
> for( int iYBlock = 0; iYBlock < nYBlocks; iYBlock++ )
> {
> for( int iXBlock = 0; iXBlock < nXBlocks; iXBlock++ )
> {
> poBand->ReadBlock( iXBlock, iYBlock, pabyData );
>
> std::cout << "test " << pabyData[25] << std::endl; //
> Where we
see that
> the array is full of 0 values...
>
> // Compute the portion of the block that is valid
> // for partial edge blocks.
> if( (iXBlock+1) * nXBlockSize > poBand->GetXSize() )
> nXValid = poBand->GetXSize() - iXBlock *
> nXBlockSize;
> else
> nXValid = nXBlockSize;
>
> if( (iYBlock+1) * nYBlockSize > poBand->GetYSize() )
> nYValid = poBand->GetYSize() - iYBlock *
> nYBlockSize;
> else
> nYValid = nYBlockSize;
> }
> }
>
> free(pabyData);
>
> GDALClose( poDataset );
>
> GDALDestroyDriverManager();
> return 0;
> }
>
>
>
>
> --
> View this message in context:
> http://osgeo-org.1560.x6.nabble.com/Issue-with-ReadBlock-tp5246218.html
> Sent from the GDAL - Dev mailing list archive at Nabble.com.
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