[gdal-dev] GDALWarpOperation.ChunkAndWarpImage on source without CRS

[Even Rouault]

Le mercredi 09 mars 2011 12:25:47, Radim Blazek a écrit :

Radim,

I don't see anything obviously wrong in your code, but the warping API is
admitedly quite tricky to use. The closest code in GDAL that you could take
insipiration from is perhaps GDALReprojectImage() in alg/gdalwarper.cpp that
does pretty similar things to your code (apps/gdalwarp.cpp does similar things
too but perhaps a bit less clear to follow).

1) The cause of the crash is the pTransformArg=0x0 passed to
GDALGenImgProjTransform () which causes a null pointer deferencing when doing
psInfo->pDstGCPTransformArg. I'm surprised that it crashes here and not the 
line before where the psInfo is already deferenced (is your GDAL build with -
O2 ? If yes, you should perhaps rebuild it without it). I don't either 
understand how you get a null pointer at that point. I don't either understand 
why the fact that the source dataset has a SRS or not has an impact at that 
point... Stepping in the code with a debugger might help to track where that 
null pointer comes from. (the line numbers didn't match the ones of my copy so 
I suspect you're not using GDAL 1.8.0, but that shouldn't be an issue however)

2) Yes, indeed pDstGCPTransformArg is unused. So there's perhaps some code
cleaning possible inside GDAL here, but that's unlikely to cause a problem per
se.

3) You should check the return value of myOperation.Initialize( myWarpOptions 
).
If the validation of the warp options failed, it would be unsafe to go on with
the warping itself.

4) myMemDsn.sprintf(
"MEM:::DATAPOINTER=%lu,PIXELS=%d,LINES=%d,BANDS=1,DATATYPE=%s,PIXELOFFSET=0,LINEOFFSET=0,BANDOFFSET=0",
( long )theBlock, thePixelWidth, thePixelHeight,  GDALGetDataTypeName((
GDALDataType )mGdalDataType[theBandNo-1] ) );  is dangerous. I think it will 
not work for a Win64 build where pointers are 64 bits but long is still 32 
bit. You could use the CPLPrintPointer() function from GDAL to format it :

    char szPointer[64];
    memset( szPointer, 0, sizeof(szPointer) );
    CPLPrintPointer( szPointer, theBlock, sizeof(szPointer) );

Best regards,

Even


> Hi,
> I am using GDALWarpOperation.ChunkAndWarpImage to read data,
> everything works well except when a source dataset does not have a CRS
> defined. Then it crashes with
> 
> #0  GDALGenImgProjTransform (pTransformArg=0x0, bDstToSrc=1,
> nPointCount=84, padfX=0xa1093f0, padfY=0xa109690, padfZ=0xa109930,
> panSuccess=0xa1090a0) at gdaltransformer.cpp:1402
> #1  0x01f56c6c in GDALWarpOperation::ComputeSourceWindow (this=0xbf7fd214,
>     nDstXOff=0, nDstYOff=0, nDstXSize=32, nDstYSize=32,
> pnSrcXOff=0xbf7fd12c, pnSrcYOff=0xbf7fd128, pnSrcXSize=0xbf7fd124,
> pnSrcYSize=0xbf7fd120) at gdalwarpoperation.cpp:1977
> 
> gdaltransformer.cpp:1402:
> 
>         pGCPTransformArg = psInfo->pDstGCPTransformArg;
> 
> but if I grep gdal for pDstGCPTransformArg it does not seem to be set at
> all.
> 
> Could you please give mi a hint? The code is here and above:
> http://trac.osgeo.org/qgis/browser/trunk/qgis/src/providers/gdal/qgsgdalpro
> vider.cpp?rev=15400#L625
> 
> Radim
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