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