| Re: Map_set limits [message #10389] |
Thu, 27 November 1997 00:00 |
Erard
Messages: 11
Registered: November 1997
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Junior Member |
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davidf@dfanning.com (David Fanning) wrote:
> St�phane Erard (Erard@ias.fr) writes:
>
>> I was trying to superimpose satellite images to a map in IDL 4, and had a
>> problem:
>>
>> I have to set the map's dimensions to the image's to get a good match,
>> using the keyword "position" in map_set.
>> After several tries I found out that the map limits are enlarged by 2% in
>> both directions (long/lat), while the dimensions are unchanged. The result
>> is that I get a map of a larger area in the dimensions of my image.
>
> Unfortunately, IDL's map projection routines are not designed
> to put a map projection on an image. (I am, however, sympathetic
> to the argument that they *should* be.) Rather, they are
> designed to put an image on a map projection.
>
I've tried this one first, yes. But it looks more like a drawing function
than anything else to me. The problem is that, when you work with remote
sensing or space images for instance, you simply need to superpose a
geographic grid to perform automatic measurements. You don't want to
degrade the image quality at all because the information you need is in
there, and it was expensive to get it. In short you need to do something
like Image_contour does for plots and images, and find out that map_set
has these weird peculiarities.
Yet, if somebody felt the need to change the maps limits in map_set there
was probably a good reason. So the question is: why? And are there
situations in which you really have to perform this strange
transformation. I find it very surprising that apparently nobody ran into
this problem before.
--
St�phane Erard
Institut d'Astrophysique Spatiale
Orsay, France
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| Re: Map_set limits [message #10397 is a reply to message #10389] |
Tue, 25 November 1997 00:00  |
davidf
Messages: 2866
Registered: September 1996
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Senior Member |
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St�phane Erard (Erard@ias.fr) writes:
> I was trying to superimpose satellite images to a map in IDL 4, and had a
> problem:
>
> I have to set the map's dimensions to the image's to get a good match,
> using the keyword "position" in map_set.
> After several tries I found out that the map limits are enlarged by 2% in
> both directions (long/lat), while the dimensions are unchanged. The result
> is that I get a map of a larger area in the dimensions of my image.
Unfortunately, IDL's map projection routines are not designed
to put a map projection on an image. (I am, however, sympathetic
to the argument that they *should* be.) Rather, they are
designed to put an image on a map projection.
The proper sequence of commands to display an image that
corresponds to the limits in the variable "mapLimits" might
look something like this:
Map_Set, /Cylindrical, Limits=mapLimits
warpedImage = Map_Image(image, xloc, yloc, xsize, ysize)
TV, warpedImage, xloc, yloc, XSize=xsize, YSize=ysize
Map_Grid
Map_Continents
Cheers,
David
-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
E-Mail: davidf@dfanning.com
Phone: 970-221-0438
Coyote's Guide to IDL Programming: http://www.dfanning.com/
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