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MathGroup Archive 2007

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Re: Anomolous behaviour of Penrose Triangle Demonstration

  • To: mathgroup at smc.vnet.net
  • Subject: [mg81135] Re: Anomolous behaviour of Penrose Triangle Demonstration
  • From: WetBlanket <Wyvern864 at gmail.com>
  • Date: Thu, 13 Sep 2007 06:32:52 -0400 (EDT)
  • References: <200709110923.FAA26497@smc.vnet.net><fc8689$lqa$1@smc.vnet.net>

On Sep 12, 2:59 am, Curtis Osterhoudt <c... at lanl.gov> wrote:
> Hi, Syd,
>
>    I have no real insight. I confirm that changing the ViewPoint prefactor
> causes the same behavior on my machine. I did not try to evaluate the code
> which allows "vp" to be changed via a slider; just rotating the graphic
> produced by the first chunk of code causes part of it to disappear (somewhat
> randomly).
>     Of course, I've been having lots of problems with my ATI drivers not being
> compatible with Mathematica 6.0's Graphics3D[] objects, so this may be a
> symptom of that.
>
>    This is on "6.0 for Linux x86 (32-bit) (June 19, 2007)".
>
> On Tuesday 11 September 2007 03:23:52 you wrote:
>
>
>
> > I would appreciate some insight regarding the Penrose Triangle
> > Demonstration which can be found at:-
>
> >            http://demonstrations.wolfram.com/PenroseTriangle/
>
> > The original source I downloaded when run on my machine displayed a
> > blank panel!
> > (The demonstration ran fine on my machine in "watch web preview" mode!)
>
> > $Version    Out[1]= "6.0 for Mac OS X x86 (32-bit) (June 19, 2007)"
>
> > The demonstration source was;-
>
> > Manipulate[
> >   cu[x_, y_, z_, d_] :=
> >    Cuboid[ {x - d/2, y - d/2, z - d/2}, {x + d/2, y + d/2, z + d/2} ];
> >   Graphics3D[
> >    {Opacity[o],
> >     cu[0, 15, 30, 7.5], cu[15, 45, 0, 7.5],
> >     Table[cu[0, 0, 15 n, 7.5], {n, 0, 3}],
> >     Table[cu[0, 15 n, 0, 7.5], {n, 3}]
> >     } ,
> >          ViewPoint -> 200 {-1, -1, 1},
> >          Boxed -> False,
> >          PlotRange -> 50 {{-1, 0.8}, {-0.6, 1}, {-0.08, 1}},
> >          ImageSize -> {400, 400}
> >    ],
> >         {{o, 1, "opacity"}, 0, 1}, TrackedSymbols :> Manipulate]
>
> > I changed the "viewpoint factor" in  ViewPoint -> 200 {-1, -1, 1}
> > above to 100{-1, -1, 1} on a hunch and the panel
> > displayed correctly.
>
> > After failing to find any documentation for the use of the "viewpoint
> > factor" I tried setting a range for vp and generating a slider in
> > addition to opacity to see the effects.
>
> > Manipulate[
> >   cu[x_, y_, z_, d_] :=
> >    Cuboid[ {x - d/2, y - d/2, z - d/2}, {x + d/2, y + d/2, z + d/2} ];
> >   Graphics3D[
> >    {Opacity[o],
> >     cu[0, 15, 30, 7.5], cu[15, 45, 0, 7.5],
> >     Table[cu[0, 0, 15 n, 7.5], {n, 0, 3}],
> >     Table[cu[0, 15 n, 0, 7.5], {n, 3}]
> >     } ,
> >          ViewPoint -> vp {-1, -1, 1},
> >          Boxed -> False,
> >          PlotRange -> 50 {{-1, 0.8}, {-0.6, 1}, {-0.08, 1}},
> >          ImageSize -> {400, 400}
> >    ],
> >         {{o, 1, "opacity"}, 0, 1}, {{vp, 10, "ViewPoint Factor"}, 10,
> > 200, 10},
> >    TrackedSymbols :> Manipulate]
>
> > The effects of using the vp slider are very odd. Bits of the graphic
> > start disappearing!
>
> > Any clues as to what is happening here would be appreciated.
>
> > Yet another strange "feature" showed up when I tried to "Save As" the
> > modified demonstration code.
>
> > I cannot successfully save the modified demonstration.
>
> > I suspect that is a WRI safeguard for protecting the integrity of the
> > Demonstrations Project (which is fine by me).
>
> > I can of course save the modified code in a new blank notebook.
>
> > Syd Geraghty
>
> --
> ==========================================================
> Curtis Osterhoudt
> cfo at remove_this.lanl.and_this.gov
> PGP Key ID: 0x4DCA2A10
> Please avoid sending me Word or PowerPoint attachments
> Seehttp://www.gnu.org/philosophy/no-word-attachments.html
> ==========================================================

I am running on a Dell XPS Laptop using Windows XT and the code seems
to work -- nothing much happens when I move the viewpoint slider --
the display moves slightly -- nothing more.

Gary



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