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Re: UTM Map Projection Produces Incorrect Results [message #78165 is a reply to message #78164]

Mon, 31 October 2011 12:20

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

alx writes:

> Changing "WGS84" to "Walbek" or to anything else will not correct the
> error in "map_proj_init"! Following my recent post (29 oct., 19:10),
> the problem in IDL code appears to be a wrong and systematic
> replacement of the given datum by a sphere as long as the projection
> identifier is larger than 20 (i.e. in case of a projection to be
> processed by GCTP library). This makes likely unusable the entire
> implementation of GCTP software in IDL: in other words, we have to
> stay with "map_set" and forget "map_proj_init".
> One may expect a fix in further IDL version.

The technical support folks are looking into this for me,
but I suspect this probably isn't a problem right now. The
CGTP projections don't actually use a datum. They use
semi-major and semi-minor axes. If these get set properly
in the parameter vector that is passed on to the GCTP
software, there shouldn't be a problem.

In the tests I've done, these seem to be passed properly,
except in the case of the UTM projection. I honestly
haven't been able to track down HOW the UTM projection works
from the code I've looked at, but I agree that it is working
*somehow* if I use the Walbeck projection.

Anyway, the folks are looking at this and promise to get
back in touch. I'll let you know if I learn anything more.

Cheers,

David

--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.idlcoyote.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: UTM Map Projection Produces Incorrect Results By: David Fanning on Mon, 31 October 2011 12:23
		Re: UTM Map Projection Produces Incorrect Results By: David Fanning on Mon, 31 October 2011 12:20
		Re: UTM Map Projection Produces Incorrect Results By: Fabzou on Mon, 31 October 2011 12:08
		Re: UTM Map Projection Produces Incorrect Results By: lecacheux.alain on Mon, 31 October 2011 11:33
		Re: UTM Map Projection Produces Incorrect Results By: David Fanning on Mon, 31 October 2011 11:21
		Re: UTM Map Projection Produces Incorrect Results By: Fabzou on Mon, 31 October 2011 11:06
		Re: UTM Map Projection Produces Incorrect Results By: David Fanning on Mon, 31 October 2011 10:42
		Re: UTM Map Projection Produces Incorrect Results By: MarioIncandenza on Mon, 31 October 2011 10:02
		Re: UTM Map Projection Produces Incorrect Results By: Andrew Cool on Thu, 03 November 2011 19:11
		Re: UTM Map Projection Produces Incorrect Results By: chris_torrence@NOSPAM on Tue, 01 November 2011 09:04

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