[gdal-dev] Warping Issues

[Even Rouault]

Martin,

Could you paste the output of gdalinfo on the .sid file on both environments,
and each time indicate what 'gdalinfo --version' reports ? It might be possible
that the issue is at the source rather than at the warping.

Even

> I seem to be having a few warping problems using OGRCoordinateTransformation
> as the warped images do not appear to have the correct co-ordinates.
> To establish what was going on I have come across a curious issue that may
> indicate the problems that I am having.
>
> On a separate machine I have QGIS 2.4.0 installed as I use this for
> verification as it also uses GDAL.
>
> I took a MrSID file (NAD83) and warped it in QGIS to a GeoTiff (WGS84).
>
> This worked successfully and produces a proper square tile with the correct
> co-ordinates.
> I then copied the command line that QGIS gives you shown below:
>
> gdalwarp -overwrite -t_srs EPSG:4326 -of GTiff
> E:/Stuff/Maps/georgiaville_se.sid E:/Stuff/Maps/testGDAL.tif
>
> and ran this on the development machine (where I have noticed the gdal
> issues) in a command prompt  using 'pure' gdal.
> This did not give any errors and a tif file was generated.
>
> However when this tif  from  the 'pure gdal'  was viewed, it was skewed with
> black borders and about 3 degrees in the longitude out and smaller error in
> the latitude. (These are the exact same errors that OGRCoordinateTransform
> gives)
>
> I then did a gdalinfo on both the generated tiff files and noticed these
> differences:
>
> From the QGIS generated file:
>
> Files: C:\Stuff\MrSID\Georgiaville_SE\testQGIS2.tif
> Size is 6133, 6131
> Origin = (-71.562566138751492,41.937520670986764)
> Pixel Size = (0.000010201993468,-0.000010201993468)
>
> From the gdal generated file:
>
> Files: C:\Stuff\MrSID\Georgiaville_SE\testGDAL.tif
> Size is 6331, 6217
> Origin = (-74.311201444644681,41.904608529793123)
> Pixel Size = (0.000010289425691,-0.000010289425691)
> (There were other differences in the Upper Left etc but these are the key
> diffs. The Coordinate System is exactly the same)
>
> What is going on? Why the differences between the two? What am I doing wrong?
> I have recently upgraded to gdal 1.11.0 and proj4 4.8.0. All the env
> variables etc are setup e.g. GDAL_DATA, PROJ_LIB and point to the correct
> directories so I must have missed something else?
>
> Hope somebody can help.
>
> Thanks
>
>
>
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