Re: Adding markers on the surface of a Plot3D?

• To: mathgroup at smc.vnet.net
• Subject: [mg89517] Re: Adding markers on the surface of a Plot3D?
• From: Szabolcs <szhorvat at gmail.com>
• Date: Wed, 11 Jun 2008 05:14:56 -0400 (EDT)
• References: <g2b4o8\$nm2\$1@smc.vnet.net> <g2dbpl\$9q9\$1@smc.vnet.net>

On Jun 11, 10:19 am, mike-g2 <michael.a.gilchr... at gmail.com> wrote:
> On Jun 7, 3:02 am, Jens-Peer Kuska <ku... at informatik.uni-leipzig.de>
> wrote:
>
>
>
> > Hi,
>
> > a) yes you are right, it' cant be done :
>
> > fun[x_, y_] := Sin[x*y]
>
> > DynamicModule[{plt},
> >   plt =Plot3D[fun[x, y], {x, -Pi, Pi}, {y, -Pi, Pi}];
> >   Manipulate[
> >    xline = ParametricPlot3D[{x, yc, fun[x, yc]}, {x, -Pi, Pi}];
> >    yline = ParametricPlot3D[{xc, y, fun[xc, y]}, {y, -Pi, Pi}];
> >    Graphics3D[{plt[[1]],
> >      Sphere[{xc, yc, fun[xc, yc]}, 0.1], {AbsoluteThickness[4],
> >       RGBColor[1, 0, 0], xline[[1]], yline[[1]]}}],
> >    {{xc, 0}, -Pi, Pi}, {{yc, 0}, -Pi, Pi}
> >    ]
> >   ]
>
> > and an other impossible example
>
> > fun[x_, y_] := Exp[-x^2 - y^2]
>
> > DynamicModule[{plt},
> >   plt =Plot3D[fun[x, y], {x, -Pi, Pi}, {y, -Pi, Pi},
> >     PlotStyle -> Opacity[0.5], PlotRange -> All];
> >   Manipulate[
> >    pnt = Append[xy, fun @@ xy];
> >    Graphics3D[{plt[[1]], Line[{Append[xy, 0], pnt}],
> >      Sphere[pnt, 0.1], {AbsoluteThickness[4], RGBColor[1, 0, 0],
> >       Line[{pnt, pnt*{1, 1, 2}}]}}, PlotRange -> All],
> >    {{xy, {0, 0}}, Slider2D}
> >    ]
> >   ]
>
> > and
>
> > Show[] evaluates to a Graphics[]/Graphics3D[] and the FrontEnd
> > show this graphics lik it show you the result of Expand[(x+1)^1000]
> > but in older Mathematica versions the FrontEnd need an other program
> > to display the PostScript and Show[] had a side effect that it paste
> > a rendered image in the Notebook.
>
> > Regards
> >    Jens
>
> > AES wrote:
> > > I'd like to highlight the two mesh lines that pass through a certain
> > > central point -- let's call it the point {xc,yc} -- on aPlot3Dby
> > > thickening those two lines relative to the other mesh lines, or giving=

> > > them a distinctive color, or . . .
>
> > > Or put a dot on the surface at the point {xc, yc, f[xc,yc]} to identif=
y
> > > this location on the surface . . .
>
> > > Or run a vertical "post" up through that point using something like
> > > Line[{xc, yc, 0}, {xc, yc, 2*f[xc,yc]}}] (with the part of the post
> > > below the surface not being seen if you look at the surface from
> > > above) . . .
>
> > > I think I've so far tested and confirmed every possible way in which
> > > each of these tasks _can't_ be done . . .
>
> > > [And would someone want to help me understand _why_  the
> > > Show[ - - - - -] command (followed by a semicolon) no longer works, or=

> > > can no longer be used, as one of a sequence of multiple expressions
> > > within a longer cell?  And why it can't even have a semicolon follow=
ing
> > > it as the last line in a cell?  I just can't envision the logic of w=
hy
> > > this was a necessary (or optional?) interface design decision -- isn't=

> > > Show[---] an expression?]
>
> So I struggled with this issue previously trying to use Epilog with
> Plot3D, but to no avail. Could some one please explain why Epilog
> won't work for adding a 3D object to a Plot3D or, if it will work,
> give an example?
>

Epilog does work with Graphics3D, but only for superposing 2D graphics
on the image.  To add 3D objects, use Show[].

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