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Re: 3D surface plots - non deletion of data inside

  • To: mathgroup at smc.vnet.net
  • Subject: [mg116365] Re: 3D surface plots - non deletion of data inside
  • From: Heike Gramberg <heike.gramberg at gmail.com>
  • Date: Sat, 12 Feb 2011 05:18:02 -0500 (EST)
  • References: <201102110919.EAA08103@smc.vnet.net>

The anomalies in GL2 are caused by the fact that your function is
undefined in the values for ph and th for which Cos[ph+th]==0.
Excluding those points from your domain, e.g. by using the option
Exclusions -> {Cos[ph+th]==0} in ParametricPlot3D, should get rid of
those.

Heike.

On 11 February 2011 09:19, Narasimham <mathma18 at hotmail.com> wrote:
>
> a=2;b=1;c=3;gl={a Cos[ph-th],b Sin[ph-th],c Sin[ph+th]}/Cos[ph+th];
> GL1=ParametricPlot3D[gl,{th,-Pi/4,Pi/4},{ph,-Pi/4,Pi/4},PlotRange-
> >{{-3,3},{-3,3},{-3,3}}]
> GL2=ParametricPlot3D[gl,{th,-Pi/3,Pi/3},{ph,-Pi/3,Pi/3},PlotRange-
> >{{-3,3},{-3,3},{-3,3}}]
> Show[GL1,GL2]
>
> Extended plot limits in GL2 beyond those of GL1 result in 3D plot that
> fail to delete undesired spurious tracing/tracking data between points
> not lying on the required surface.Like 'pen up' data in earlier
> graphing s/w. It is OK may be to plot an enclosed solid, but not for a
> surface. The difficulty also appeared in earlier Mathematica versions.
> Is there then, no work around possible?
>
> Best Regards
> Narasimham
>


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