Re: Problems updating Graphics3D Polygons

*To*: mathgroup at smc.vnet.net*Subject*: [mg77625] Re: Problems updating Graphics3D Polygons*From*: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>*Date*: Thu, 14 Jun 2007 05:19:42 -0400 (EDT)*Organization*: The Open University, Milton Keynes, UK*References*: <f4ol3r$6uj$1@smc.vnet.net>

chuck009 wrote: > Hello guys. Can you help me write a function which takes a Graphics3D object and multiplies the z-coordinate of each point of all the polygons by a ratio. This is what I have so far but it's not working: > > In[473]:= > ExpandZ[g_,ratio_]:= > g/.Polygon[pts_]:>Polygon[{#[[1]],#[[2]],#[[3]]*ratio}& /@pts]; > > When I test it with this simple Graphics3D object: > > gobject=Graphics3D[{Polygon[{{0.,0.5,1.28},{0.,0.,1.},{0.5,0.,1.28},{0.5, > 0.5,1.64}}],Polygon[{{ > 0.5,0.5,1.64},{0.5,0.,1.28},{1.,0.,2.71},{1.,0.5,3.49}}]}]; > > It doesn't do anything: > > g2=Expand[gobject,2] -----^^^^^^ Should have been *ExpandZ* > InputForm[g2] > > Out[475]= > â??Graphics3Dâ?? > > Out[476]//InputForm= > Graphics3D[{Polygon[{{0., 0.5, 1.28}, {0., 0., 1.}, > {0.5, 0., 1.28}, {0.5, 0.5, 1.64}}], > Polygon[{{0.5, 0.5, 1.64}, {0.5, 0., 1.28}, > {1., 0., 2.71}, {1., 0.5, 3.49}}]}] > > I'll keep working on it. Thanks! > Your code is fine. However, you have made a spelling mistake: you do not want Expand bur *ExpandZ* (that is why it is useful to use a lowercase letter at the beginning of the name of a user define function :-) In[1]:= ExpandZ[g_, ratio_] := g /. Polygon[pts_] :> Polygon[({#1[[1]], #1[[2]], #1[[3]]*ratio} & ) /@ pts]; gobject = Graphics3D[{Polygon[{{0., 0.5, 1.28}, {0., 0., 1.}, {0.5, 0., 1.28}, {0.5, 0.5, 1.64}}], Polygon[{{0.5, 0.5, 1.64}, {0.5, 0., 1.28}, {1., 0., 2.71}, {1., 0.5, 3.49}}]}]; g2 = ExpandZ[gobject, 2] InputForm[g2] Out[4]//InputForm= Graphics3D[{Polygon[{{0., 0.5, 2.56}, {0., 0., 2.}, {0.5, 0., 2.56}, {0.5, 0.5, 3.28}}], Polygon[{{0.5, 0.5, 3.28}, {0.5, 0., 2.56}, {1., 0., 5.42}, {1., 0.5, 6.98}}]}] Regards, Jean-Marc