[GRASS5] datum conversion problems

[Roger Miller]

On Sunday 27 November 2005 10:34, Paul Kelly wrote:

> In particular, make sure you have the line
> nadgrids: conus
> in your NAD27 location. That's the only think I can think that would
> have changed the functionality; see the warning at the end of the 5.3.0
> release announcement
> http://www.geog.uni-hannover.de/grass/announces/announce_grass530.html

Paul,

Thanks very much.  Running g.setproj on the nad27 location fixed the problem.

I've just got to complain about this...

Could the developers find a less obscure place to document this change than in 
the release announcement?  This is a change that probably effected every 
GRASS 5.0 user in North America -- apparently not a large number.  I have 
found no documentation in the GRASS 5.3.0 distribution that mentions the 
change or the need to rerun g.setproj for (probably) all of their North 
American locations.  The GRASS 6.0.1 distribution includes a text document on 
migrating from GRASS 5.0 to GRASS 5.7 and it says nothing at all about the 
need to rerun g.setproj.

Is there any documentation out there on the proj library api?  Before posting 
my original letter I wrote an example program that ran pj_transform in 
isolation.  I read the available documentation on the proj library, in the 
source code and in the header files and they said nothing about the need to 
provide a "nadgrids" parameter for anything.  There are also quite a few 
other details in the library that could use some significant documentation.

Finally, I expect that most users in North America will regard it as an error 
if an nad27<->nad83 conversion is done with something other than the nad 
grids.  I don't know why GRASS would allow for other operations.


Roger Miller