[Proj] WGS84 parameters in epsg:31370 and 28992 (Belgian and Dutch coordinate systems)

[Jan Hartmann]

Frank Warmerdam wrote:
> What is not clear to me is why the Amersfoort parameters were commented
> out.  Curse me for note making clearer notes on why things are in the
> state they are.  If you would like to file a ticket against libgeotiff
> explaining why the above parameters are appropriate I can re-enable them
> in libgeotiff and they will in time flow downstream into GDAL, PROJ.4,
> PostGIS, etc.
>
>   
Done.

> As you note, no datum shift at all is applied unless both source and
> destination datum have a defined relationship to WGS84 (towgs84, datum
> shift file, etc).
>
>   
In the case of the Belgian and Dutch (and all other) systems, where only 
the ellipses are different but not translated or rotated, this can be 
confusing. In those cases you don't need the towgs84 numbers, and in 
many cases they are not even known. And when they are not known, you 
cannot even get a correct transformation, as the ellipse conversion will 
never be computed without the towgs84 parameter. Wouldn't it be an idea 
to apply the ellipse transformation when both epsg-strings  have 
+nadgrids=@null?

Jan