[gdal-dev] GTiff format does not preserve WKT EXTENSION nodes?

[Frank Warmerdam]

On 11-12-02 05:31 AM, Etienne Tourigny wrote:
> Hi all,
>
> I have been trying to override the MODIS WKT definition (derived from
> the source HDF4 files using gdal_translate), which apparently is not
> sufficient for correct transformations.
> The correct srs is  '+proj=sinu +R=6371007.181 +nadgrids=@null
> +wktext', whereas the one stored in GTiff files is '+proj=sinu
> +lon_0=0 +x_0=0 +y_0=0 +a=6371007.181 +b=6371007.181 +units=m +no_defs
> '
>
> I tried to override the projection ref with gdal_translate, but the
> resulting file (in GTiff format) does not keep the EXTENSION nodes.
>
> Examples below.
>
> Is this a limitation of GTiff format that cannot be fixed?  Is there
> another format (except VRT) that can keep EXTENSION nodes?
> The workaround is to override the SRS with -s_srs='...' when a
> transformation is needed, but it would be better if the file itself
> could store that information.

Etienne,

Most of the raster formats with their own way of representing coordinate
systems will not support extension nodes and will tend to be somewhat
lossy in other aspects of the coordinate system as well.  Any format that
is completely dependent on .aux.xml files for the coordinate system (like
png, jpeg, etc) will preserve it.

It seems like their ought to be a way to force GeoTIFF to write and use the
.aux.xml instead of internal tags so as to preserve the full SRS definition
but nothing immediately comes to mind.

Best regards,
-- 
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