       Re: Model the surface of an ellipsoid

• To: mathgroup at smc.vnet.net
• Subject: [mg93564] Re: Model the surface of an ellipsoid
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 14 Nov 2008 06:36:31 -0500 (EST)
• Organization: Uni Leipzig
• References: <gfgqib\$dm1\$1@smc.vnet.net> <gfh3ca\$g1d\$1@smc.vnet.net> <gfimlb\$g3d\$1@smc.vnet.net>

```Hi,

after simple algebra you end up with

R^2 == r^2 + R^2*d^2/D^2

and since you have 4 variables, you
can fix one of the variables

With[{D = 1},
ContourPlot3D[
R^2 == r^2 + R^2*d^2/D^2, {r, -2, 2}, {R, -2, 2}, {d, -2, 2}]]

or make an interactive version.

Manipulate[
ContourPlot3D[
R^2 == r^2 + R^2*d^2/D^2, {r, -2, 2}, {R, -2, 2}, {d, -2,
2}], {D, -2, 2}]

Regards
Jens

Mayneord wrote:
> On Nov 13, 12:34 pm, Jens-Peer Kuska <ku... at informatik.uni-leipzig.de>
> wrote:
>> Hi,
>>
>> and
>>
>> http://mathworld.wolfram.com/Ellipsoid.html
>>
>> has no parametric or implicit equation for you ?
> books/Surfaces/Ellipsoid.nb
>> ??
>>
>> Regards
>>    Jens
>
> Hi Jens,
>
> when i wrote this post, I was sure that i will get a reply from you
> first ;-)
>
> I did not understand anything from that it seems to be too much of
> mathematics to me.
> In my case i have only 4 unknown parameters ( 1 = Sqrt[r^2/R^2 + d^2/
> D^2] ). Typically, also shown in the websitehttp://mathworld.wolfram.com/El=
> lipsoid.html,
> for a ellipsoidal there must at least three coordinates. But the
> equation which is i have seems to be different. please tell me if am
> wrong. Please understand i am using mathematica 5.2.
>
> I used an ImplicitPlot like this i get only 2D plot.
> ImplicitPlot[Sqrt[(x^2/9) + (y^2/4)] == 1, {x, -3, 3}]
>
> My question is for 3D it is more complicated?  do i need to use much
> of trigonometry for the angles?
>
> thanks again
>
> May
>
>

```

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