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| Re: METEOSAT navigation [message #34856 is a reply to message #34855] |
Wed, 23 April 2003 07:16  |
Liam E. Gumley
Messages: 378
Registered: January 2000
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Senior Member |
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"Roberto Hernandez" <rhernandez@euve.org> wrote in message
news:9886e8f4.0304230034.1cec4b91@posting.google.com...
> Hello all,
> I'm trying to overlap coastal boundaries to a METEOSAT image (B
> format, that covers the European, North African and Middle East
> regions) with the MAP_SET command.
> I need to use the native projection -geostationary- and specify the
> LIMIT option as an eight-element vector, althouth the top pixels are
> on space. I try to substitute them with the extreme coordinates on
> Earth's visible disc, but the boundaries don't match properly.
>
> Any ideas will be appreciated.
You may have better luck with the SCALE keyword for MAP_SET (instead of
LIMIT). As a guide, a map scale of 4E6 corresponds to a map resolution of
1000 meters, assuming 40.0 pixels per centimeter in IDL direct graphics,
i.e.,
IDL> print, !d.x_px_cm
40.0000
This value may be slightly different on other platforms. So the trick is to
create a map projection with the appropriate scale, e.g.
clat = 0.0
clon = 140.0 ; longitude for Meteosat 7
scale = 16E6 ; map resolution of 4000 meters
map_set, clat, clon, scale=(scale * (!d.x_px_cm / 40.0)), $
/orthographic, position=[0.0, 0.0, 1.0, 1.0], /noerase
map_continents
This command assumes the center pixel of the image is at [clat, clon], so it
may not work if the image has been clipped in some way (i.e., it's not a
full disk image).
Another source of information is Kelly Dean's site at
http://www.cira.colostate.edu/special/csuidl/overview.htm
that might be helpful.
Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com
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