[gdal-dev] Error in GDALWarp to NWT_GRD

[James Ramm]

I may very well be computing the file size wrong, my calculation is:

1024 + nXSize * nYSize * 2

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
> > > > http://lists.osgeo.org/mailman/listinfo/gdal-dev
> > >
> > > --
> > > Spatialys - Geospatial professional services
> > > http://www.spatialys.com
>
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/gdal-dev/attachments/20160720/d5c2ab01/attachment.html>