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Re: Newbie needs help...

Bruce Bowler (bbowler@bigelow.org) writes:
> I've lurked for a while and now it's time to ask for help...

Uh, oh. Trouble here. Newbies and de-cloaked lurkers
always ask the most difficult questions. :-(
> I have some satellite data that I need to a) display a portion of on the
> globe and b) extract the data at various positions.
> Towards that end, I've snarfed up image_map.pro from Liam Gumley's site
> and regrid.pro and tvim.pro from ESRG.  They both do sort of what I want
> but neither gets me "all the way there".
> Liam's does a nice job of displaying the image and letting me plop a
> grid and continent map on top but he's got this big fat caveat in the
> code that says "This procedure was designed for display purposes *only*"
> (emphasis his) and some bits about dire consequences if used otherwise.  
> regrid does a good job of "regularizing" the data and tvim makes a nice
> plot with scales and color bars and all that nice stuff (without the
> "dire consequences" :-) but when I try and slap a grid or continental
> blobs on the image, they puke complaining that "the current device must
> have mapping coordinates"...
> In either case, I'm left with the problem of mapping a lat/lon that the
> user inputs to a pixel on the screen (or an element in an array, as the
> case may be).

What you want to do--slap a lat/lon grid on top of
an image--is reasonable. It's just that IDL is not
the software you should be using to do it. :-)

IDL works the other way around. It allows you to
slap an image on top of a lat/lon grid. Sometimes
the result is similar, but if you hold pixel values
to be sacrosanct, then you are almost always disappointed
in what you can do with IDL.

Liam offers his big fat caveat with good reason. He figured out
a clever way of making the image display *look* right, but
he is rightfully offering no guarantees about the numbers. 

Liam can fill you in on the details of this better than
I can, but if you persist I can recommend "getting used
to disappointment" as the appropriate spiritual practice.


David Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438 E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155