[gdal-dev] Doubt about memory raster

[Frank Warmerdam]

Jorge Arévalo wrote:
> In MEM driver page: http://www.gdal.org/frmt_mem.html says:
> 
> "PIXELOFFSET: Offset in bytes between the start of one pixel and the
> next on the same scanline. (optional)"
> 
> The data pixels are bytes, but the pixeloffset is 2. I suppose in the
> example, the data pixels are interlaced (one scan line starts on
> pabyBigMem and the other in pabyBigMem + 1), and for this reason
> pixeloffset = 2.
> 
> How do you specify this (if pixels are interlaced or not) when
> creating the raster and adding the bands? Maybe this is not necessary,
> and you specify this when reading or writing, but then, why in
> GDALDatasetRasterIO the pixeloffset and lineoffset are set to 0?

Jorge,

To address such an existing array, the options to GDALAddBand()
would need to include DATAPOINTER, PIXELOFFSET and LINEOFFSET.
DATAPOINTER for the first call to addband would be pabyBigMem
and it would be pabyBigMem+1 for the second band.   In both
cases PIXELOFFSET would be 2 and LINEOFFSET would be
PIXELOFFSET*(image_width_in_pixels).

Best regards,
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