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Map Projection Question [message #70871]

Fri, 14 May 2010 08:46

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Folks,

Here area a couple of questions I don't have time to
research this morning.

How can I tell if the current data coordinate system
is a map coordinate system? And, how can I tell the
difference between a lat/lon map coordinate system and
an XY map coordinate system?

Cheers,

David

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

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Re: Map Projection Question [message #70980 is a reply to message #70871]

Tue, 18 May 2010 01:00

Klemen
Messages: 80
Registered: July 2009

Member

Hi David,

In general, you should look at the metadata. It also helps if you
know, what kind of data you are looking at - then you can use your
common sense (e.g. resolution of 0.00833333 stands probably not for
meters but for decimal degrees).

To do it automatically: in Envi it is quite easy: envi_open_data_file
+ envi_file_query should do it. This is the easiest way if your
dataset contains georeference information. In IDL read the codes from
e.g. Geotiff and then compare them with
http://www.remotesensing.org/geotiff/spec/contents.html. In the case
of shapefiles you can look at the PRJ file and check the codes on the
ESRI web site, you can start by:
http://resources.arcgis.com/content/kbase?fa=articleShow& ;d=23025 or
http://webhelp.esri.com/arcgisdesktop/9.3/index.cfm?id=113&a mp;pid=112&topicname=List_of_supported_map_projections

I hope it helps somehow, but this was not an easy question.
Cheers, Klemen

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