[GRASSLIST:2199] Re: Another problem with r.proj

[Eric G. Miller]

On Sat, Jul 28, 2001 at 07:57:02AM -0700, Rich Shepard wrote:
[snip]
That all looks okay, except:

> 	PROJ_UNITS:
> unit: unknown
> units: unknowns
> meter: 1

Does it help if you change the PROJ_UNITS to?

unit: meter
units: meters
meter: 1.0

Also, it looks like you need to specify the input "mapset" for the
location (i.e. "spc").

>   Once I get past this hurdle, I want to change the datum from NAD27 to
> NAD83. I know there's a module to do this, but the name escapes me now.

Actually, the datum transformation needs to be done via geodetic
coordinates following the inverse projection from UTM.  Unfortunately,
the projection routines in GRASS don't do this at the present. 

It may or may not be easier to use i.rectify to transform the DEM --
provided you can find suitable control coordinates. (hint: select 6 or 8
points spread across the input source; transform them to geodetic
coordinates; use m.datum.shift to get the corresponding datum shifted
geodetic coordinates; project the coordinates to your target projection;
voila, you have control points in both coordinate systems).

-- 
Eric G. Miller <egm2 at jps.net>