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Re: Range of "Spherical Coordinates" in SPHER_HARM [message #62846 is a reply to message #62824]

Thu, 09 October 2008 06:22

Kenneth P. Bowman
Messages: 585
Registered: May 2000

Senior Member

In article <gcku0s$4t1$1@aioe.org>,
"Karlo Janos" <idl.20.beamer2@spamgourmet.com> wrote:

> Hello all!
>
> I am a little bit confused about the usage of spherical coordinates in
> the function SPHER_HARM.
> The first parameter should be the azimuthal angle theta (in the help
> document named 'polar' or 'colatitudinal') and the second parameter the
> polar angle phi (in the help document named 'azimuthal' or
> 'longitudinal').
> According to the example code at the end of the help page the range for
> theta seems to be [0; pi] as I would have presumed. But what is the
> range for phi? [0; 2pi] or [-pi; pi]? In some functions (where the
> keyword '/DEGREES' is possible) it must be the latter, relating to the
> coordinate system of the earth. But what about SPHER_HARM? I did not
> find any explanation about the definition of theta and phi there.
> Does anybody see clearly here?
> Greets
>
> Karlo

Spherical harmonics are simply sines and cosines in the azimuthal
(longitudinal) direction, so it does not matter whether you
use [0, 2 pi] or [-pi, pi]. Use whichever convention you want, but be
consistent or you will end up with phase errors.

And, as is usually the case with IDL, the easiest approach is to
try it and see if you get what you want.

Ken Bowman

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[Message index]

		Re: Range of "Spherical Coordinates" in SPHER_HARM By: jameskuyper on Sun, 12 October 2008 11:45
		Re: Range of "Spherical Coordinates" in SPHER_HARM By: Karlo Janos on Sun, 12 October 2008 04:41
		Re: Range of "Spherical Coordinates" in SPHER_HARM By: Kenneth P. Bowman on Thu, 09 October 2008 06:22
		Re: Range of "Spherical Coordinates" in SPHER_HARM By: jameskuyper on Thu, 09 October 2008 10:18
		Re: Range of "Spherical Coordinates" in SPHER_HARM By: Karlo Janos on Mon, 13 October 2008 00:22

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