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Re: displaying an image in simple geographic coordinates [message #54282 is a reply to message #54165]

Tue, 29 May 2007 10:36

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

Matt wrote:
> Any reason why my !RADEG values appear to be different than the ones
> posted above? When I run the same commands I get different results:
>
> IDL> map_set, /continents, /grid
> IDL> print,map_proj_forward([-90,90],[-45,45])*!RADEG
> -90.000001 -45.000001
> 90.000001 45.000001
>
> Not a huge difference but it seems to me like the conversion factor
> should be the same, right?

This looks like a floating point round-off error to me. See <http://
www.dfanning.com/math_tips/sky_is_falling.html> for relevant
information. We are probably running on different platforms. I
performed that test on my Linux desktop machine; where "uname -srvmp"
gives:

Linux 2.4.21-47.EL #1 Tue Aug 1 08:56:24 EDT 2006 i686 i686

If you're using a different platform, then it's quite feasible for
your round-off errors to be a little different from the ones I get on
my machine.

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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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