# Re: Polar to spherical coordinates

• Subject: Re: Polar to spherical coordinates
• From: Patrick Ford <pford(at)bcm.tmc.edu>
• Date: Thu, 27 Apr 2000 21:30:14 -0500
• Newsgroups: comp.lang.idl-pvwave
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• References: <8e1rpu\$k36@gazette.bcm.tmc.edu> <MPG.136e22dd5bfafe0c989aeb@news.frii.com>
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```Oh, if what I wanted was that easy.  What I would like is more akin to
the MAP_IMAGE function. I want to convert a 2D array "image"  into a 3D
array "image"  such as a polar projection to a sphere ( 3D array) and
back again.  Using the WHERE function and the CV-COORD function I have
partially done what I need to do.  It looks like I will need to create
a look-up-table (LUT) to translate the coordinates.

It still seems like there must be a trivial solution other than to
create a LUT and its inverse. I vaguely recall from some math-sci
course I took in college 20 or so years ago that we used transform to
"transform" from one domain to another. This is what I am looking for,
a function that will do this transform.   If I make one, I will post it
so that it will be decreased in size by 80% and speed by 300% as usual
since I still think in FORTRAN or C and not IDL.

Thanks

In article <MPG.136e22dd5bfafe0c989aeb@news.frii.com>, David Fanning
<davidf@dfanning.com> wrote:

> Patrick V. Ford (pford@bcm.tmc.edu) writes:
>
> > I have a problem that is screaming at me that there must be a simpler
> > solution in IDL than I have devised.  I am attempting to relearn IDL,
> > after months of being away from it, and the math after decades from it and
> > I have not found a built-in procedure that does the trick.
> >
> > The problem in its, simplest  form, is that I want to take a 2-D polar
> > plot and transform it into a 3-D hemisphere and vice versa.   More
> > accurately, a polar plot to a 3-D hemi-ellipsoid with varying axes and
> > thickness, i.e. more than just a surface plot.  The manner that I am
> > thinking how to do this is to sample the polar plot along its radius and
> > map it to the hemisphere(with for loops). It seems to me that this is
> > likely common in IDL to map from polar to spherical coordinates and to
> > warp shapes.  Since I don't wish to reinvent the wheel, and not a good
> > wheel at that, I would appreciate being pointed in the right direction.
>
> I'd start by trying to use CV_COORD to map from polar to
> spherical coordinates.
>
> Cheers,
>
> David

```