| Re: Weird Map Projection [message #49897] |
Wed, 30 August 2006 13:12 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Kenneth Bowman writes:
> In the example, there are no labels for 90 and 270, so it is not possible to
> tell whether longitude actually decreases to the right or whether it is just
> labeled in a "creative" way. (That is, the longitudes could be 360, 90, 180,
> 270, 0 or 360, 270, 180, 90, 0.)
>
> If you really need longitude to decrease to the right, assuming the data array
> and associate longitudes vary like this
>
> IDL> x = 360 - 90*lindgen(5)
> IDL> print, x
> 360 270 180 90 0
>
> Just flip the coordinates (not the data) like this
>
> IDL> x1 = -x + 360
> IDL> print, x1
> 0 90 180 270 360
>
> and use a conventional MAP_SET. Then
>
> CONTOUR, z, x1, y, ...
>
> and label "manually"
>
> FOR i = 0, 360, 90 DO YXOUTS, x1[i], y0, STRTRIM(x[i], 2)
>
>
> If your data has longitude *increasing* to the right, but you want to plot it
> backwards, flip the
Well, shoot, that's what I thought. I just assumed it
was wrong. :-)
Thanks,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui.
(Opata Indian saying, meaning "Perhaps thou speakest truth.")
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| Re: Weird Map Projection [message #49898 is a reply to message #49897] |
Wed, 30 August 2006 13:02  |
K. Bowman
Messages: 330
Registered: May 2000
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Senior Member |
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In article <MPG.1f5f88cbea27da24989ca3@news.frii.com>,
David Fanning <davidf@dfanning.com> wrote:
> Folks,
>
> OK, here is a question from the mail bag that I don't know
> the answer to.
>
> How can I set up a map projection space, using MAP_SET
> if possible, that has longitude 360 on the LEFT and
> longitude 0 of the RIGHT.
In the example, there are no labels for 90 and 270, so it is not possible to
tell whether longitude actually decreases to the right or whether it is just
labeled in a "creative" way. (That is, the longitudes could be 360, 90, 180,
270, 0 or 360, 270, 180, 90, 0.)
If you really need longitude to decrease to the right, assuming the data array
and associate longitudes vary like this
IDL> x = 360 - 90*lindgen(5)
IDL> print, x
360 270 180 90 0
Just flip the coordinates (not the data) like this
IDL> x1 = -x + 360
IDL> print, x1
0 90 180 270 360
and use a conventional MAP_SET. Then
CONTOUR, z, x1, y, ...
and label "manually"
FOR i = 0, 360, 90 DO YXOUTS, x1[i], y0, STRTRIM(x[i], 2)
If your data has longitude *increasing* to the right, but you want to plot it
backwards, flip the data, not the longitudes.
Ken Bowman
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