[gdal-dev] Extract data from a.dem file

[Even Rouault]

Yes , what you see is expected.

The prototype of RasterIO() is :

RasterIO( flag, x, y, width, height, buffer, buffer_width, buffer_height, 
gdal_type, pixel_offset, line_offset)

so that means that you ask the extraction of the window [x, x + with-1] x [y, 
y + height -1] to be stored in a buffer_width x buffer_height buffer.

so if you set x to be non-null, you cannot ask for the full XSize to be read, 
the maximum value for width is XSize - x.

See http://gdal.org/classGDALRasterBand.html#5497e8d29e743ee9177202cb3f61c3c7 
for the full reference.

Le lundi 06 septembre 2010 17:25:31, Carmelo Terrasi a écrit :
> Hello everybody,
> I'm trying to figure out how to get elevation from a .dem file.
> 
> I opened the file:
> ...
> pointerToDataSet=(GDALDataset*) GDALOpen("myFile.dem", GA_ReadOnly);
> ...
> 
> 
> So I caught a grid as a 371x371 matrix, but I can read only the first line,
> so the first 371 elevations... the error is: *...Access window out of range
> in RasterIO()...*
> 
> I mean If I put coordinates like (*0*, *somethingelse*) where 0<*
> somethingelse<*370:
> ...
> pointerToBand->RasterIO( GF_Read, 0, *somethingelse*, nXSize, 1, elevation,
> nXSize, 1,  GDT_Float32, 0, 0 );
> ...
> that's ok
> 
> 
> 
> Instead if I put coordinates (*x*, *somethingelse*) where
> 0<*somethingelse*<370 and
> 0<*x*:
> ...
> pointerToBand->RasterIO( GF_Read, *x*, *somethingelse*
> , nXSize, 1, elevation, nXSize, 1,  GDT_Float32, 0, 0 );
> ...
> that doesn't work :(
> 
> I opened myFile.dem with a text editor and I've seen the whole matrix as a
> linecode values...
> There's something I cannot understand obviously, any tips would be really
> appreciated, thanks in advance,
> Regards
> Carmelo