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Re: Map projections [message #27968 is a reply to message #15827]

Mon, 12 November 2001 08:16

Liam E. Gumley
Messages: 378
Registered: January 2000

Senior Member

James Kuyper wrote:
> Is there any way to get at the coordinate conversion function for the
> currently active map projection? I'm talking about a function that takes
> a physical position in latitude and longitude coordinates, and converts
> it into an image position using either data, device, or normal
> coordinates. It doesn't matter which; once the position is in any one of
> those forms, I can get the others by using CONVERT_COORD. Such functions
> have to exist in order for IDL to perform mapping, but they don't seem
> to be publically exposed. I'd also like to have access to the inverse
> function, to get a lat/lon corresponding to an image position.

James,

When a map projection is active, longitude and latitude correspond to
x/y data coordinates. Therefore CONVERT_COORD will allow you to obtain
the device or normal coordinates for a given lon/lat. For example:

window, /free
map_set, 45, -90, scale=20e6, /usa
lon = -89.6
lat = 43.5
print, convert_coord(lon, lat, /data, /to_device)
326.465 217.622 0.000000
print, convert_coord(lon, lat, /data, /to_normal)
0.510102 0.425044 0.000000

Cheers,
Liam.
Practical IDL Programming
http://www.gumley.com/

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[Message index]

		Map Projections and Contour Plots. By: Grady Daub on Thu, 10 June 1999 00:00
		Re: Map Projections and Contour Plots. By: Martin Schultz on Wed, 16 June 1999 00:00
		Re: Map Projections and Contour Plots. By: wmc on Wed, 16 June 1999 00:00
		Re: Map Projections and Contour Plots. By: Grady Daub on Tue, 15 June 1999 00:00
		Re: Map projections By: Liam E. Gumley on Mon, 12 November 2001 08:16

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