| Re: Display and Navigate Image in IDL 8.2 [message #81329 is a reply to message #81328] |
Thu, 06 September 2012 10:24   |
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DavidF[1]
Messages: 94
Registered: April 2012
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Member |
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Alain writes:
> Looking at your map display problem, I got the following issue:
>
> centerlat = 40.6000d
> centerlon = -105.1000d
> xrange = [-11711131.0d, -11688226.0d]
> yrange = [4914254.0d, 4937159.5d]
> map = map_proj_init('Mercator', ELLIPSOID='WGS 84', CENTER_LONGITUDE=0, CENTER_LATITUDE=0)
> print, map_proj_inverse(mean(xrange), mean(yrange), MAP_STRUCTURE=map)
> ; -105.10000 40.410029
>
> I should have found 40.6° for the latitude, is'nt it ?
>
> print, map_proj_inverse(xrange, yrange, MAP_STRUCTURE=map)
>
> ; -105.20288 40.331647
> ; -104.99712 40.488320
>
> Same thing regarding the latitude range boundaries which seem sligthly different
>
> from those in your PNG example (40.525 and 40.675, by eye).
The numbers could well be off a little bit. Google doesn't (I suppose
deliberately) supply these images in GeoTiff format, so I had to determine
the pixel per meter value from other published data. It involved some
detective work and assumptions (see cgGoogle_MetersPerPixel). Using
the numbers I used, however, my markers lined up exactly with Google's
own markers, so I'm guessing the numbers are close enough for my use.
But, all this is beside the point. I really want to know how
to navigate and display this image using function graphics
routines. I can use whatever projected meter numbers I like,
and I *still* can't see the image in a display window. If I
could, maybe I could work on the details of whether my map
projection numbers are totally accurate. ;-)
Cheers,
David
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