[Proj] using an NTv2 grid to apply a slight shift to coordinates in a metric CS

[Andre Joost]

Just re-read the manual:

The shift is done with lat/lon values, and the source and target 
ellipsoid are given in the gsa/gsb file. Bbut I am not sure if they are 
actually used by Proj4.

Proj.4 always refers to WGS84 as target, so that ellipsoid should be the 
target ellipsoid.

The individual shift values are in seconds of lat and lon.

Greetings,
André Joost