| AVHRR Image Mapping Problem [message #51852] |
Fri, 15 December 2006 07:42  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Folks,
Does anyone have any experience working with AVHRR NDVI
image data or Albers map projection? I have obtained
the data, which is of the African continent from here:
ftp://ftp.glcf.umiacs.umd.edu/glcf/GIMMS/Regional/Albers/Afr ica
The image is in an Albers Conical equal area projection
and the centers of the four corner pixels are known from
the documentation:
; YX coordinates of the four corners (LL, UL, UR, LR)
longitude = [-23.49, -24.6, 64.523, 63.414]
latitude = [-42.243, 43.711, 43.712, -42.242]
This is a GeoTiff file, so I also pull the Standard
Parallels out of the geotiff information stored in
the file (they are -19 and 21).
I follow the method outlined on this page (which has
worked perfectly for a polar stereo map projection),
using instead of a Stereo projection, an Albers
projection with standard parallels:
http://www.dfanning.com/map_tips/precipmap.html
The method *ALMOST* works! :-)
But the continental outlines do not QUITE line up properly.
You can see my result here:
http://www.dfanning.com/misc/africa.jpg
Do you think this might be an Albers projection problem?
A difference between MAP_PROJ_INIT and MAP_SET? (I have
tried different DATUMS with no change in effect.)
Or, do you think this might just be right? :-(
Cheers,
David
P.S. Don't worry about the colors. They are still screwed up.
--
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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