[mapguide-users] Incorrect NAD27 to NAD83 coordinate conversions

[Kayne M. Morvant]

Hi,

I have a sdf data source with a coordinate system of Lat/Long NAD27.  I 
also have a map created in Mapguide Studio and the coordinate system is set 
to "UTM83-15 (UTM83-15)".  When I view the map, the coordinates are off by 
about 13 meters on the x coord. and 225 meters on the y coord.

It appeared to me that the appropriate datum shifts were not being applied 
(and were not actually part of the default installation), so I did the 
following:
- I stopped the Mapguide server.
- I downloaded the datum shift grids (proj-datumgrid-1.3.zip from 
remotesensing.org/proj) and unzipped into the nad directory.
- I executed a 'make clean', 'make', and 'make install' from the proj root 
directory.
- I re-started the Mapguide server.

When I completed the steps above, I viewed my map again but the coordinates 
were still incorrect.

I have two questions:
1) Did I follow the correct steps to add NAD27/NAD83 datum shifting support 
for proj4?
2) How does Mapguide know whether or not to apply the datum shifts?

Note: I am running MGOS 1.1 on Linux.

-Kayne