[gdal-dev] Fwd: How to reuse memory pointer of GDAL Memory driver

[Even Rouault]

On Monday 06 June 2016 10:45:47 Pol Monsó Purtí wrote:
> THanks Mateusz,
> 
> You're right. I'm trying it as we speak.
> 
> In my case I have a std::vector<GByte*> of the 3 bands, where the GByte*
> are allocated in the heap with new GByte[width*height]. I guess that won't
> work because the three bands have to be one single memory chunk, am I
> right? I guess the only solution is to switch to single band float and
> merge rgb to float. I'd prefer not having to refactor the rest of the code.


> Is it possible to have a different address for each band?

Yes, create a dataset with 0 band and then add each band with the 
GDALDataset::AddBand() method

See http://gdal.org/frmt_mem.html :
"""The MEM format is one of the few that supports the AddBand() method. The 
AddBand() method supports DATAPOINTER, PIXELOFFSET and LINEOFFSET options to 
reference an existing memory array."""

> 
> All this is to support jpg as output. All the operations are done in my
> GByte array and it's only at the end that I create the dataset and image.
> At the moment I create a Tiff and finally createcopy to jpg.
> 
> On Fri, Jun 3, 2016 at 9:10 PM, Mateusz Loskot <mateusz at loskot.net> wrote:
> > On 3 June 2016 at 20:45, Pol Monsó Purtí <lluna.nova at gmail.com> wrote:
> > > I've seen this mysterious article http://www.gdal.org/frmt_mem.html
> > 
> > which
> > 
> > > references the `DATAPOINTER` option. I've seen another reference
> > > [here](
> > 
> > https://lists.osgeo.org/pipermail/gdal-dev/2006-November/010583.html)
> > 
> > > which does
> > 
> > sprintf(filename,"MEM:::DATAPOINTER=%d,PIXELS=%d,LINES=%d,BANDS=1,DATATYPE
> > 
=%d,PIXELOFFSET=0,LINEOFFSET=0,BANDOFFSET=0",datpt,pixels,lines,datatype);> 
> > >     dataset = GDALOpen(filename,GA_Update);
> > > 
> > > How would this translate to c++?
> > 
> > The line above is valid C++, isn't it.
> > If you followed to Frank's answer [1], you'd see it slightly corrected
> > but the technique remains the same.
> > 
> > [1] https://lists.osgeo.org/pipermail/gdal-dev/2006-November/010603.html
> > 
> > Best regards,
> > --
> > Mateusz Loskot, http://mateusz.loskot.net

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