| Re: Latitude/longitude, contours, map_set, iMap? [message #43912 is a reply to message #43910] |
Tue, 03 May 2005 19:40  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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jamiesmyth_uni@yahoo.ca writes:
> I should caveat this by saying I need to plot data on maps about twice
> a year and every time it is more difficult than I expect it to be.
I suspect most of it is figuring out how to get EMACS installed
again. :-)
> I have some atmospheric model data for temperature (originally grib data)
> on a latitude/longitude grid and I'm having quite a difficult time
> plotting it with the iMap and/or the map_set routines. The first
> problem I have is that the longitude data goes from 0-360 degrees. So
> I have:
>
> LAT FLOAT Array[73]
> LON FLOAT Array[96]
> PRESSURE FLOAT Array[22]
> TEMPERATURE FLOAT Array[73, 96, 22]
>
> where the latitdes go from -90 to +90 in 2.5 degree steps and the
> longitudes go from 0 to +360 in 3.75 degree steps. I've read some past
> messages on how to re-work the longitude to -180 to 180 degrees and
> have:
>
> lon_new = lon - (long(lon)/180L)*360.0
>
> Do I have to also alter the temperature array to reflect this change or
> can I simply plot the data with:
>
> imap, transpose(data.pv[*,*,0]), data.lon, data.lat
No, you don't have to change your temperature values.
They will be fine.
> or
>
> map_set, /continents, /mercator, /isotropic
> contour, transpose(data.pv[*,*,0]), data.xlon, data.xlat, /overplot,
> nlevels=12
>
> The first command brings up a dialog box for the 'gridding wizzard' but
> when I click ok, nothing happens. The second looks 'more-or-less' ok
> but there seems to be a gap at 0 degrees. The gap is rather apparent
> when I fill the contours... Do I need to re-grid or triangulate the
> data? Is there a quick way to do any of this?
You need to specify the center of your map projection on
the MAP_SET command. Here is an article that explains what
the problem is:
http://www.dfanning.com/tips/map_center.html
> I'd much prefer to use imap here as it makes figures that look much
> better in powerpoint.
Yeah, well, I don't know anything about iTools. (My tutorials
don't seem to be arriving anymore. I don't know why.) But a quick
look at a half dozen graphics keywords would probably improve
your direct graphic results. In particular, I would have a look
at FONT, THICK, CHARTHICK, and maybe CHARSIZE.
> Any ideas and help would be much appreciated... I'm supposed to be
> putting these figures (along with some polar stereographic projections)
> into a talk for thursday! Reaching for brown-paper bag... taking
> deep-breaths...
Oh, you are almost there! Just a few more minutes. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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