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Re: displaying an image in simple geographic coordinates [message #54224 is a reply to message #54165]

Fri, 25 May 2007 13:54

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

Matt wrote:
> does anyone know how i can display an image in simple geographic
> coordinates using IDL? all documentation that i have read deals with
> reprojection images to various projections or reprojecting a window to
> a given image's projection. geographic coordinates is never listed as
> an option in any of these functions. maybe it's because i'm dealing

In IDL, the default projection is cylindrical, which is (almost) the
same thing as what you're calling geographic coordinates. In this
projection, the x coordinate is the longitude in radians, and the y
coordinate is the latitude in radians.

IDL> map_set, /continents, /grid
IDL> print,map_proj_forward([-90,90],[-45,45])*!RADEG
-89.999995 -44.999998
89.999995 44.999998

You can also use MAP_PROJ_INIT, but you have to override the default
sphere radius:

IDL> proj = MAP_PROJ_INIT('Equirectangular', SPHERE_RADIUS=1.0)
IDL> print,map_proj_forward([-90,90],[-45,45],map_structure=proj) *!
RADEG
-89.999995 -44.999998
89.999995 44.999998

Alternatively, you could simplify by building the conversion factor
into the projection itself:
IDL> proj = MAP_PROJ_INIT('Equirectangular', SPHERE_RADIUS=!RADEG)
IDL> print,map_proj_forward([-90,90],
[-45,45],map_structure=proj)
-89.999995 -44.999998
89.999995 44.999998

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[Message index]

		displaying an image in simple geographic coordinates By: Matt[1] on Thu, 24 May 2007 13:44
		Re: displaying an image in simple geographic coordinates By: James Kuyper on Fri, 25 May 2007 13:54
		Re: displaying an image in simple geographic coordinates By: Matt[1] on Tue, 29 May 2007 08:19
		Re: displaying an image in simple geographic coordinates By: James Kuyper on Tue, 29 May 2007 10:36

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