[gdal-dev] gdal.AutoCreateWarpedVRT returning different results than osr.CoordinateTransformation

[Frank Warmerdam]

On 12-05-04 03:39 PM, Billy Newman wrote:
> I ran a quick test and confirmed that gdal.AutoCreateWarpedVRT is returning
> different results than osr.CoordinateTransformation.
>
> I.E. I opened a file using:
> Dataset dataset = gdal.Open("/images/image.tif");
>
> I grabbed the corner point and used
> osr.CoordinateTransformation.TransformPoint(), to transform the point into
> EPSG:4326.
>
> I warped the dataset using gdal.AutoCreateWarpedVRT, grabbed the corner point
> and the corner point was a little different.
>
> I am not sure if that is expected behavior or not.  Hopefully I am just missing
> some static files and one of the transformations was not quite right.  I tried
> all the different sampling algos available for the AutoCreateWarpedVRT and that
> did not make a huge difference.
>
> Is warp using a different method to transform the points?  If so is that
> transformation available via the API?
>
> I understand that not all calcs may be exact between these two but I would
> expect the corner point to be almost exact.

Billy,

Generally speaking the extents of the warped VRT will be somewhat larger
than the original to capture the irregular shape of the source image after
warping into the target coordinate system.

Best regards,
-- 
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