AW: [Gdal-dev] Grid based transformation with ogr2ogr

[uwe.schmitz at lverma.nrw.de]

Hi Frank,

> 
> Uwe,
> 
> Unfortunately gdalwarp uses OGC Well Known Text as the 
> internal coordinate
> system representation and that does not include any support 
> for grid files.
> NAD27/NAD83 grid shift files are handled as a special case.
> 
> So the PROJ.4 representation is parsed and converted to WKT, and then
> converted back to PROJ.4 format to do the actual coordinate 
> transformation.
> But by then the grid list is lost.
> 
> Unfortunately, there is no current way to accomplish what you 
> want with
> gdalwarp.  I would encourage you to file a bug report.  I think I may
> make an non-standard extension or two to WKT to allow 
> transporting some
> of these values I need for PROJ.4.
> 

ok, I see the problem. I will file a bug report
as soon as I manage to log in (It seems that I've
forgotten my password... and I'm waiting for the
mail to set a new one).

Meanwhile... is it possible to do the datum-shift
with the +towgs84=x,y,z switch, or is it lost in
the same way? And if so, where has +towgs84 to
be placed? In the -s_srs or the -t_srs switch?

Many thanks in advance
Uwe