Re: Newbie needs help...

[davidf(at)dfanning.com (David Fanning)]

Bruce Bowler (bbowler@bigelow.org) writes:

> karmic confusion reigns supreme... 

Now we *are* getting somewhere... :-)

> I have this big huge array (here
> after referred to as a BHA) of data (BHAd) an equally sized BHA of
> latitudes (BHAlat) of each point in BHAd and another BHA of longitudes
> (BHAlon) of each point in BHAd.  NB, row x of BHAlat is not constant,
> neither is column y of BHAlon
> 
> I understand map_set, I understand map_grid, I understand map_continents
> (well, not in the tao-ist sense of the word).  map_image is where I'm
> getting confused...  how does map_image know about BHAlat and BHAlon
> when they are not inputs to the process? 

Ah, this is what IDL doesn't do. Liam does this
by taking each one of your pixels (I'm paraphrasing
here) and putting it over on your map one by one.
Then he sees that he has a very holey map (pun
intended in this case), so he "fills it in" with
some kind of dilation thing, if I remember correctly.
(Where *is* Liam, anyway!?) That's why he doesn't
want you to trust the numbers. He has had to fudge
them a bit. But they look great!

I guess if I were in your shoes, I might try to
reformat the part of the image I was interested 
in onto a regular lat/lon grid. I'd probably try
to use TRIANGULATE and TRIGRID first, to see if
that would work. You will jimmy the numbers, of
course, but no way around that if you want to use
IDL. Then, I would put the regular lat/lon image
on the map using Map_Image.

There are probably other ways to warp the image
onto the map, but there is no getting around the
need to do it. What you would prefer, I'm sure, is
to have a map warped to the image. But this is NOT
possible in IDL.

Then, I would get the specified value from the
regular lat/lon grid, if I couldn't figure out
a way to get a better number from my original
array. Remember that the display *IS* only a 
display. You are not really looking at your data.
All you want to do is have the display *represent*
your data in a more or less faithful way. I think
Liam's solution is as good as you are likely to
get for actually displaying your data.

Once you have the display, getting the actual value
out of your data set shouldn't be terribly hard.
You might need some kind of look-up table for
indexing, but this should be fairly straightforward.

Cheers,

David

P.S. Let's just say I really wish Liam would step
in here. :-(

-- 
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