[Proj] Problems using grid shift files

[Paul Kelly]

On Fri, 23 Jan 2009, Mikael Rittri wrote:

> I think cs2cs normally assumes that a grid shift file will transform a national datum to WGS84.
> So I don't know how chenyx06.gsb can be used by cs2cs, but perhaps some pipe
> construction could be used.

Specify the gridshift file as part of the PROJ.4 description of the CH1903 
system, and use a +towgs84=0,0,0 datum parameter set for the CH1903+ 
location. Something along those lines should work I think, but the 
co-ordinates would need to be transformed again to get to WGS84.

Paul