[GRASS5] datum conversion problems
Roger Miller
roger at spinn.net
Sun Nov 27 12:27:38 EST 2005
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
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