[GRASSLIST:7958] Re: Fwd: Re: nad27/nad83 datum conversion for canada using Ntv2

[Paul Kelly]

On Wed, 17 Aug 2005, Feng Tan wrote:

> I just did some testing about nad27/nad83 datum conversion for a point in
> Alberta, Canada using GRASS6.0 comparing with ESRI ARCGIS9.1, following is
> the result, it has about +-100m difference with or without NTV2_0.GSB. I wish
> GRASS can implement newer version of Canadian National Transformation
> NTV2_0.GSB nad27/nad83 datum shift grid file soon, so we can use GRASS more
> confidently.

GRASS (and PROJ.4) *can* use NTv2 GSB (binary) files and has been able to 
since the datum shifting support was added in 5.3. I'm not sure what 
your problem is here. What are you trying to change?
Put the gsb file in the $GISBASE/etc/nad directory and edit the PROJ_INFO 
file for your NAD27 location to point to the new file.

Paul