| Day/Night Terminator on Map Projection [message #48311] |
Fri, 07 April 2006 17:26  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Hi Folks,
Does anyone have IDL code for calculating the day/night
terminator on a map projection? Or perhaps an example of
a map in which you have done this?
If the code is not proprietary, maybe I'll write an article
about this. It can't be the first time someone has needed
such a thing. Direct graphics, is what has been requested of
me. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Day/Night Terminator on Map Projection [message #48347 is a reply to message #48311] |
Thu, 13 April 2006 16:15  |
JD Smith
Messages: 850
Registered: December 1999
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Senior Member |
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On Fri, 07 Apr 2006 18:26:15 -0600, David Fanning wrote:
> Hi Folks,
>
> Does anyone have IDL code for calculating the day/night
> terminator on a map projection? Or perhaps an example of
> a map in which you have done this?
>
> If the code is not proprietary, maybe I'll write an article
> about this. It can't be the first time someone has needed
> such a thing. Direct graphics, is what has been requested of
> me. :-)
I guess you saw this page too:
http://fermi.jhuapl.edu/s1r/idl/s1rlib/sphere/earth.html#sun clock
Those twilight bands are cool (usually defined as where the sun is 6, 12,
and 18 degrees below the horizon). You might have some fun adding those.
JD
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| Re: Day/Night Terminator on Map Projection [message #48363 is a reply to message #48311] |
Thu, 13 April 2006 08:20 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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David Fanning writes:
> You can see the code I came up with and a nice picture
> here:
>
> http://www.dfanning.com/map_tips/terminator.html
>
> To run the code, you will need to have both the Coyote
> Library and the JHUAPL Library on your IDL path.
Yikes! Matt Savoie just pointed out a very interesting
problem with the code on LINUX machines. It seems that
on LINUX (and possibly UNIX, I don't know) that issuing
a MAP_SET command changes the state of !P.MULTI. This
causes problems with TVIMAGE that I wasn't aware of.
Here is an IDL session on my LINUX box:
IDL> Print, !P.MULTI
0 0 0 0 0
IDL> Map_Set, /Cylindrical
IDL> Print, !P.MULTI
-1 0 0 0 0
An obvious workaround is to put a !P.MULTI=0 command
after every MAP_SET, but maybe there is something less
ugly than that available. I'll poke around a bit.
But in the meantime, I've put new code on my web page
that contains the workaround.
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Day/Night Terminator on Map Projection [message #48365 is a reply to message #48311] |
Thu, 13 April 2006 05:10 |
Haje Korth
Messages: 651
Registered: May 1997
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Senior Member |
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Thanks for sharing! Haje
"David Fanning" <davidf@dfanning.com> wrote in message
news:MPG.1ea796ded95b4343989c0c@news.frii.com...
> David Fanning writes:
>
>> Does anyone have IDL code for calculating the day/night
>> terminator on a map projection? Or perhaps an example of
>> a map in which you have done this?
>
> Thanks to Kelly Dean and Andrew Cool for suppling me
> with a few (slightly buggy!) examples of how to do this. :-)
>
> After spending most of the day scratching my head and
> pondering yet again the shear beauty of Ray Sterner's
> JHUAPL code, I finally came up with something I like.
>
> Rather than just drawing the day/night terminator, I wanted
> to see it in living color. So I used the AVHRR data set that
> comes in the IDL demo directory for this purpose. It makes
> a very pretty map, if I do say so myself!
>
> You can see the code I came up with and a nice picture
> here:
>
> http://www.dfanning.com/map_tips/terminator.html
>
> To run the code, you will need to have both the Coyote
> Library and the JHUAPL Library on your IDL path.
>
> I'll probably spend some time tomorrow making a little
> stand-alone application out of this with widgets so you
> can change the time interactively. It's more interesting
> than I would have thought to change the time and watch
> the sun and shadows move though the day and year. :-)
>
> Cheers,
>
> David
> --
> David Fanning, Ph.D.
> Fanning Software Consulting, Inc.
> Coyote's Guide to IDL Programming: http://www.dfanning.com/
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| Re: Day/Night Terminator on Map Projection [message #48366 is a reply to message #48311] |
Wed, 12 April 2006 23:00 |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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David Fanning writes:
> Does anyone have IDL code for calculating the day/night
> terminator on a map projection? Or perhaps an example of
> a map in which you have done this?
Thanks to Kelly Dean and Andrew Cool for suppling me
with a few (slightly buggy!) examples of how to do this. :-)
After spending most of the day scratching my head and
pondering yet again the shear beauty of Ray Sterner's
JHUAPL code, I finally came up with something I like.
Rather than just drawing the day/night terminator, I wanted
to see it in living color. So I used the AVHRR data set that
comes in the IDL demo directory for this purpose. It makes
a very pretty map, if I do say so myself!
You can see the code I came up with and a nice picture
here:
http://www.dfanning.com/map_tips/terminator.html
To run the code, you will need to have both the Coyote
Library and the JHUAPL Library on your IDL path.
I'll probably spend some time tomorrow making a little
stand-alone application out of this with widgets so you
can change the time interactively. It's more interesting
than I would have thought to change the time and watch
the sun and shadows move though the day and year. :-)
Cheers,
David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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