[Gdal-dev] Re: pfnPreWarpChunkProcessor

[Frank Warmerdam]

Jason Hughes wrote:
> I was looking into using this hook.  Is there a reason this is called twice 
> for large files?  Does that mean I only get part of the image in 
> pKern->papabySrcImage?  How should i loop through this data member? I do 
> know the papabySrcImage[band][data] 

Jason,

The warper breaks the whole image into chunks based on some maximum amount
of memory allowed for use in the warper. So for large images there will
be many chunks, and so many invocations of the chunk processor.

The chunk pre-processor is passed in a GDALWarpKernel pointer which contains
all the imagery and some other configuration option for the chunk.  You can
update the input imagery "in place" in the papabySrcImage array.  This array
is an array of pointers to chunks of imagery for each of the bands.  The
chunks of will be of type eWorkingDataType, and will be nSrcXSize * nSrcYSize.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent