[GRASSLIST:1872] Re: Importing USGS SDTS DLG maps from differing datums? I'm confused. [very long]

Eric G. Miller egm2 at jps.net
Thu May 24 21:55:06 EDT 2001

On Thu, May 24, 2001 at 03:38:52PM -0600, Roger S. Miller wrote:
> On Thu, 24 May 2001, Tom Russo wrote:
> > Simple statement of the question: How can I import two DLGs that were created
> > using different geodetic data (NAD27 and NAD83) into the same grass location?
> > v.proj seems to be the way to do it, but I tried and it didn't work as I
> > expected it to.
> Tom,
> I think you found an actual problem.  I'm nearby, so I took a local
> interest in your problem.

Shortcoming actually.  Don't think GRASS actually can handle datum
transformations yet (though there's no reason it shouldn't).  I believe
Andreas added the ability to specify a datum, and some functions that
will do datum transformations, but these haven't been tied into existing
routines for inverse and forward projections.  I think do_proj.c
(libes/proj/) will need to be hacked to do datum transformations when the
input/output datums are different.  It simply doesn't look, and libproj
does not do datum shifts. 

Eric G. Miller <egm2 at jps.net>

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