| Map_Proj_Inverse Bug? [message #64427] |
Mon, 29 December 2008 12:48 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Folks,
I've been fooling around with map coordinates today, and
I've run into a strange result with Map_Proj_Inverse.
Here is the sequence of commands:
IDL> mapStruct = Map_Proj_Init(109) ; Transverse Mercator
IDL> Print, mapStruct.uv_box[[0,2]], mapStruct.uv_box[[1,3]]
-6411813.8 6411813.8 ; longitude
-9997887.3 9997887.3 ; latitude
## Looks good here, what I expect.
IDL> Print, Map_Proj_Inverse(mapStruct.uv_box[[0,2]], $
IDL> mapStruct.uv_box[[1,3]], $
IDL> MAP_STRUCTURE=mapStruct)
0.00000000 -90.000000
0.00000000 90.000000
## The longitude values are in the first column and the latitude
values in the second column. I had expected to see -180 and 180
in the first column, but I guess I can understand 0, 0 well enough.
IDL> Print, Map_Proj_Inverse(mapStruct.uv_box[[0,2]], $
IDL> [0,0], $
IDL> MAP_STRUCTURE=mapStruct)
-50.317650 0.00000000
50.317650 0.00000000
## Whoa! What happened here!? The longitude values depend on latitude?
IDL> Print, Map_Proj_Inverse([0,0], $
IDL> mapStruct.uv_box[[1,3]], $
IDL> MAP_STRUCTURE=mapStruct)
0.00000000 -90.000000
0.00000000 90.000000
## The other way around seems to be OK.
Any explanation for why my longitude values are depending on
the latitude values I use in Map_Proj_Init? Do you think this
could be a bug?
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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