| Polar to spherical coordinates [message #19807] |
Mon, 24 April 2000 00:00  |
pford
Messages: 33
Registered: September 1996
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Member |
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Greetings:
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.
Thank you,
Patrick Ford, MD
Baylor College of Medicine
pford@bcm.tmc.edu
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| Re: Polar to spherical coordinates [message #19911 is a reply to message #19807] |
Thu, 27 April 2000 00:00  |
Patrick V. Ford
Messages: 14
Registered: February 1997
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Junior Member |
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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
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