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MathGroup Archive 2001

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RE: ParamtricPlot3D

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32130] RE: [mg32119] ParamtricPlot3D
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 29 Dec 2001 00:46:50 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

Erich,

You are double covering the sphere because you are using too wide a domain
for the v variable. Try

ParametricPlot3D[{Sin[u]*Cos[v], Cos[u]*Cos[v], Sin[v]}, {u, -Pi,
      Pi}, {v, -Pi/2, Pi/2}];

Because of the approximate nature of the calculations, Mathematica obtains
interweaved surfaces which it has a very difficult time in rendering. In
general with 3D graphics in Mathematica it is best to avoid unnecessarily
interweaved surfaces.

David Park
djmp at earthlink.net
http://home.earthlink.net/~djmp/

> From: Erich Neuwirth [mailto:erich.neuwirth at univie.ac.at]
To: mathgroup at smc.vnet.net
>
> when displaying s sphere with
>
> ParametricPlot3D[{Sin[u]*Cos[v],Cos[u]*Cos[v],Sin[v]},{u,-Pi,Pi},{
> v,-Pi,Pi}]
>
> the resultig display does NOT have a convex surface.
>
> and so does
> ParametricPlot3D[{Sin[u]*Sin[v],Cos[u]*Sin[v],Cos[v]},{u,-Pi,Pi},{
> v,-Pi,Pi}]
>
> in the second case, in the horizontal crosscuts
> ther points go "in and out", one is close, ons is farther next is closer
> ...
> to the center.
>
> since i want to create 3d objects in other programs,
> this is not good.
>
> setting PlotPoints higher
> does not completely solve the problem.
> is there an easy solution?
>
> --
> Erich Neuwirth, Computer Supported Didactics Working Group
> Visit our SunSITE at http://sunsite.univie.ac.at
> Phone: +43-1-4277-38624 Fax: +43-1-4277-9386
>



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