[gdal-dev] Mismatched output from listgeo/gdalwarp/cs2cs

[Even Rouault]

> This leads me to conclude that without an +datum reference or a +towgs84
> parameter value proj (and possibly gdalwarp) no longer performs any
> datum transformation whatsoever. In other words it is not converting
> from one ellipsoid to the other via geocentric. Is that correct? If so,
> what is the rationale behind this choice? Our GIS toolkit takes a
> different approach and defaults to +towgs84=0,0,0 instead. My hunch is
> that this difference in default interpretation is the cause of the
> horizontal shift I'm seeing.

Yes exactly, this is the new intended behaviour of proj4. See the following
entry in the FAQ :
http://trac.osgeo.org/proj/wiki/FAQ#WhydoIgetdifferentresultswith4.5.0and4.6.0

>
> Thanks in advance for any help,
>
> Pepijn Van Eeckhoudt
>