[gdal-dev] Error in GDALWarp to NWT_GRD

[Even Rouault]

Le mercredi 20 juillet 2016 15:55:37, James Ramm a écrit :
> I may very well be computing the file size wrong, my calculation is:
> 
> 1024 + nXSize * nYSize * 2

This might perhaps be not the issue in your case, but I warned you before 
about the potential int32 overflow. You should cast one of nXSize or nYSize to 
vsi_l_offset. 


> 
> 1024 is the size of the header. Data on disk is written as an unsigned
> short hence * 2.
> 
> I think this is correct when comparing with calculation to seek to a given
> block offset in IReadBlock/IWriteBlock:
> 
> 1024 + nRecordSize * static_cast<vsi_l_offset>(nBlockYOff),
> 
> Where nRecordSize = nBlockXSize * 2
> 
> VSIFTruncateL would be preferred - I will keep looking at it to find what
> Im doing wrong.
> 
> On 20 July 2016 at 14:35, Even Rouault <even.rouault at spatialys.com> wrote:
> > Le mercredi 20 juillet 2016 15:29:37, James Ramm a écrit :
> > > The only 'fix' I can get working is to return a zero-filled array if
> > > the call to VSIFReadL fails in IReadBlock.
> > > 
> > > Given that ReadBlock checks whether the block index is valid, I think
> > > it
> > 
> > is
> > 
> > > safe to assume that if IReadBlock is called, the data is expected to be
> > > retrievable (i.e. VSIFReadL in IReadBlock would not fail due to a user
> > > requesting a block that is out of bounds as that raise an error much
> > > earlier), is it acceptable to do this?
> > > 
> > > Any reason for VSIFReadL to fail for a valid block index where an error
> > > would be preferable to a zero'd array?
> > 
> > If the file is corrupted/truncated, it might be appropriate to return an
> > error.
> > Or if the operating system doesn't manage to read the block (disk
> > corruption)
> > 
> > I still don't get why VSIFTruncateL() wouldn't do the job. Are you sure
> > you are computing correctly the file size when extending it ?
> > 
> > > I also tried to see whether VSIGetRangeStatusL could be of any help.
> > > Interestingly, for the newly created raster (without any data added),
> > > it returns VSI_RANGE_STATUS_DATA for the very first block and
> > > VSI_RANGE_STATUS_HOLE
> > > for subsequent blocks.
> > 
> > The granularity of the information is linked a disk sector (4 KB ? might
> > depend on the filesystem) so it is not surprising that the first block
> > returns
> > DATA given there's an header.
> > 
> > > On 14 July 2016 at 13:26, Even Rouault <even.rouault at spatialys.com>
> > 
> > wrote:
> > > > Le jeudi 14 juillet 2016 13:07:42, jramm a écrit :
> > > > > I added the following to the end of the Create method in
> > > > > 
> > > > > frmts/northwood/grddataset.cpp:
> > > > >     vsi_l_offset nFileSize = 1024 + nXSize * nYSize * 2;
> > > > 
> > > > --> beware of the potential int32 overflow in nXSize * nYSize
> > > > 
> > > > >     if (VSIFTruncateL(poDS->fp, nFileSize) != 0) {
> > > > >     
> > > > >               CPLError(CE_Failure, CPLE_FileIO,
> > > > >               
> > > > >                               "Failed to allocate space for GRD
> > 
> > file");
> > 
> > > > >               delete poDS;
> > > > >               return NULL;
> > > > >     
> > > > >     }
> > > > >     poDS->FlushCache(); // Write the header to disk.
> > > > > 
> > > > > Unfortunately still receiving the error. I wonder if it would be
> > 
> > better
> > 
> > > > if
> > > > 
> > > > > I explicitly write the zeros with VSIFWriteL?
> > > > 
> > > > No, that's what VSIFTruncateL() is supposed to do, in a smarter way
> > > > depending
> > > > on filesystem capabilities.
> > > > 
> > > > > --
> > 
> > > > > View this message in context:
> > http://osgeo-org.1560.x6.nabble.com/Error-in-GDALWarp-to-NWT-GRD-tp527613
> > 
> > > > 6
> > > > 
> > > > > p5276347.html Sent from the GDAL - Dev mailing list archive at
> > > > 
> > > > Nabble.com.
> > > > 
> > > > > _______________________________________________
> > > > > gdal-dev mailing list
> > > > > gdal-dev at lists.osgeo.org
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> > > > 
> > > > --
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> > 
> > --
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> > http://www.spatialys.com

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