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Re: More Map Projection Madness [message #78251 is a reply to message #78248]

Tue, 01 November 2011 09:35

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

David Fanning writes:

> So, bottom line. Don't use the UTM projection with
> the WGS84 datum, don't use map projection names at
> all, and get VERY familiar with proj4 so you can
> check to see if anything at all that comes out of
> an IDL map projection is accurate. :-(

OK, the situation is more complicated than this.

Apparently, I chose a perverse example. Although,
I have to admit, over the past couple of months
I have the distinct feeling that examples are
choosing me, rather than visa versa. :-(

It seems the name "Albers Equal Area" is ambiguous.
In fact, it seems to choose the old MAP_SET routine
"Albers Equal Area Conic" as the map projection.
To make it choose the same projection as projection
103, I have to set the CGTP keyword.

alberMap = MAP_PROJ_INIT('albers equal area', /GCTP, $
DATUM='WGS 84', $
CENTER_LATITUDE=geotag.PROJNATORIGINLATGEOKEY, $
CENTER_LONGITUDE=geotag.PROJNATORIGINLONGGEOKEY, $
STANDARD_PAR1=geotag.PROJSTDPARALLEL1GEOKEY, $
STANDARD_PAR2=geotag.PROJSTDPARALLEL2GEOKEY)

Then, this behaves identically to the the projection when
I use the projection index 103.

But, this contradicts what I learned this morning
about the WGS84 datum, because here is behaves
perfectly.

I appreciate Chris's attempt to shed light on this subject.
It is greatly appreciated. But, I am still very confused.
I understand this may not be completely ITTVIS's fault. :-)

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: More Map Projection Madness By: David Fanning on Thu, 03 November 2011 11:43
		Re: More Map Projection Madness By: David Fanning on Tue, 01 November 2011 13:20
		Re: More Map Projection Madness By: David Fanning on Tue, 01 November 2011 11:02
		Re: More Map Projection Madness By: chris_torrence@NOSPAM on Tue, 01 November 2011 10:30
		Re: More Map Projection Madness By: David Fanning on Tue, 01 November 2011 10:32
		Re: More Map Projection Madness By: David Fanning on Tue, 01 November 2011 09:35
		Re: More Map Projection Madness By: Paul Van Delst[1] on Mon, 07 November 2011 08:19
		Re: More Map Projection Madness By: David Fanning on Fri, 04 November 2011 10:34

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