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Another Map Projection Problem with Map_Proj_Init [message #78416]

Mon, 28 November 2011 07:50

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Folks,

I have discovered another map projection problem this morning.
It seems Map_Proj_Init is calculating incorrect UV ranges
(they are wrong by 10 degrees) when the center latitude is
not 0.0. Here is a short test program:

FOR j=0,10 DO BEGIN
center_lon = 0 > j*36.0d < 360.0
mapStruct = Map_Proj_Init(117, CENTER_LONGITUDE=center_lon)
print, center_lon, mapStruct.uv_box[[0,2]]

ll = Map_Proj_Inverse(mapStruct.uv_box[[0,2]], $
mapStruct.uv_box[[1,3]], MAP_STRUCTURE=mapStruct)
print, center_lon, ll[0,0], ll[0,1]
print, ""
ENDFOR
END

Here are the results. The numbers should be symmetric,
but you can see they are not.

0.000000 -20015077. 20015077.
0.000000 180.00000 -180.00000

36.0000 -19570298. 19347908.
36.0000 -140.00000 -150.00000

72.0000 -19125518. 19792688.
72.0000 -100.00000 -110.00000

108.000 -19792688. 19125518.
108.000 -70.000000 -80.000000

144.000 -19347908. 19570298.
144.000 -30.000000 -40.000000

180.000 -20015077. 18903129.
180.000 0.00000000 -10.000000

216.000 -19570298. 19347908.
216.000 40.000000 30.000000

252.000 -19125518. 19792688.
252.000 80.000000 70.000000

288.000 -19792688. 19125518.
288.000 110.00000 100.00000

324.000 -19347908. 19570298.
324.000 150.00000 140.00000

360.000 -20015077. 20015066.
360.000 180.00000 179.99990

I couldn't figure out why my grid lines were always getting
screwed up when I calculated them using the UV range! :-(

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]

		Another Map Projection Problem with Map_Proj_Init By: David Fanning on Mon, 28 November 2011 07:50
		Re: Another Map Projection Problem with Map_Proj_Init By: David Fanning on Tue, 06 December 2011 05:35
		Re: Another Map Projection Problem with Map_Proj_Init By: Fabzou on Tue, 06 December 2011 02:32
		Re: Another Map Projection Problem with Map_Proj_Init By: David Fanning on Mon, 05 December 2011 16:43

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