Re: Adding markers on the surface of a Plot3D?

• To: mathgroup at smc.vnet.net
• Subject: [mg89506] Re: Adding markers on the surface of a Plot3D?
• From: mike-g2 <michael.a.gilchrist at gmail.com>
• Date: Wed, 11 Jun 2008 03:18:31 -0400 (EDT)
• References: <g2b4o8\$nm2\$1@smc.vnet.net> <g2dbpl\$9q9\$1@smc.vnet.net>

```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 identify
> > 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 following
> > it as the last line in a cell?  I just can't envision the logic of why
> > 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?

Thanks.

Mike

```

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