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Re: AVHRR Image Mapping Problem [message #51983 is a reply to message #51852] Fri, 15 December 2006 13:42 Go to previous messageGo to previous message
David Fanning is currently offline  David Fanning
Messages: 11724
Registered: August 2001
Senior Member
kuyper@wizard.net writes:

> I would guess that the vector data is stored as latitude and longitude,
> and converted automatically to the current projection. The vector data
> could be inaccurate, but the more plausible assumption is that the real
> parameters of the Albers projection used to create the raster data are
> different from the documented values of those parameters; that's the
> possibility I was trying to explore.

This is pretty much my take on the problem, too.
I can believe the vector data supplied with IDL could
be inaccurate (I used the low-resolution data and not
the high), but the fact that the GSHHS high resolution
vector data shows the same problem leads me to think
it is a map projection problem of some sort.

I guess one other possibility is that the parallels
are correct, but the corners of the image are not.
(I did verify that the numbers I use are the same
as those listed in the documentation.) But changing
numbers in a random way reminds me too much of object
graphics programming to get too excited about THAT
possibility. :-(

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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