Re: Adding markers on the surface of a Plot3D?

*To*: mathgroup at smc.vnet.net*Subject*: [mg89373] Re: Adding markers on the surface of a Plot3D?*From*: Szabolcs <szhorvat at gmail.com>*Date*: Sat, 7 Jun 2008 03:00:11 -0400 (EDT)*References*: <g2b4o8$nm2$1@smc.vnet.net>

On Jun 6, 1:49 pm, AES <sieg... at stanford.edu> 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 a Plot3D by > 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 . . . > Is this what you are trying to achieve? fun[x_, y_] := Exp[-(x^2 + y^2)] Show[ Plot3D[fun[x, y], {x, -3, 3}, {y, -3, 3}, PlotRange -> All, Mesh -> {{{0, Thick}, Sequence @@ Table[{x}, {x, -3, 3, .5}]}, {{0, Thick}, Sequence @@ Table[{x}, {x, -3, 3, .5}]}}], Graphics3D[{{Red, PointSize[0.03], Point[{0, 0, fun[0, 0]}]}, {Thick, Line[{{0, 0, fun[0, 0]}, {0, 0, 1.2 fun[0, 0]}}]}}]] > [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?] It has been explained many times on this list that in Mathematica 6, the graphics are not shown as a side effect. Instead they are simply the return values of plotting functions. Graphics[] objects are formatted in a special way in StandardForm/TraditionalForm (the actual graphics are displayed instead of the expression representing them). This behaviour is much more consistent with the design of Mathematica and IMO a big step forward. If you need to show graphics as a side effect, Print[] them. But I am sure that you were already aware of this.