[gdal-dev] writing a subregion with GDALRasterIO

[Even Rouault]

Le mardi 08 mai 2012 15:52:11, Joaquim Luis a écrit :
> Hi,
> 
> I am having some troubles in writing a sub-region on an array with
> GDALRasterIO.
> 
> The story is this. GMT internal grid arrays have a padding of 2 rows and
> 2 columns around the 'true data region' that is used for boundary
> conditions but that need to be striped off upon saving on file.
> 
> The following works well when I previously moved all real data in the
> 'data' array to the beginning of the array. That is, when I sort of
> removed the the padding zone.
> 
>    hDstDS = GDALCreate( hDriver, "mem", nx, ny, n_bands, typeCLASS, NULL );
> ....
>     GDALRasterIO( hBand, GF_Write, 0, 0, nx, ny, data, nx, ny,
> typeCLASS, 0, 0 );
> 
> However, I would like to avoid that step and read directly the zone of
> interest from 'data', which because of the padding has actually
> (nx+4)x(ny+4) elements. So I tried
> 
>      GDALRasterIO( hBand, GF_Write, 2, 2, nx, ny, data, nx+4, ny+4,
> typeCLASS, 0, 0 );

--> This call is indeed not valid according to the semantics of GDALRasterIO() 
and the error message you get is expected.

Untested, but you could rather try something like (assuming your datatype is 
Byte)

GDALRasterIO( hBand, GF_Write, 0, 0, nx, ny, data + 2 * nx + 2, nx, ny,
 typeCLASS, 0, nx + 4 );

to offset the data buffer to the (2,2) pixel and providing a line stride of nx + 
4.