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Re: Coordinates from Graphics3D images

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  • Subject: [mg117476] Re: Coordinates from Graphics3D images
  • From: Heike Gramberg <heike.gramberg at>
  • Date: Sat, 19 Mar 2011 06:17:39 -0500 (EST)

If you're using mathematica 8 and your 3D object consists of polygons, you =
could use Texture. You would get the same effect as the ColorFunction in Pa=
rametricPlot3D when you take the texture data to be a suitable 3-dimensiona=
l matrix and the VertexTexturCoordinates of your Graphics3D object equal to=
 its (scaled) vertex coordinates. There is an example in basic examples sec=
tion in the documentation for VertexTextureCoordinates where they do exactl=
y that. From there on I guess you can use the same functions as before.


On 18 Mar 2011, at 10:59, Russell Chipman wrote:

> Dear MathGroup
> I am searching for a way to find the {x,y,z} coordinates at every pixel i=
n a Graphics3D view.
> I found a way to do this in ParametricPlot3D using ColorFunction, but Gra=
phics3D does not accept ColorFunction as an option.
> To get the pixels at every coordinate ParametricPlot3D view, I encode the=
 coordinates into an RGBColor image, then recover them from the three color=
 planes.  Because the arguments to RGBColor are 0 < x < 1, first I scale al=
l coordinates into this range.  Later I unscale them.
> Take the example function
> ff[u_,v_]:=={(2+Cos[v])Cos[u]/\[Pi],(2+Cos[v])Sin[u]/\[Pi],Sin[v]}
> and the view
> ParametricPlot3D[ff[u,v],{u,0,2\[Pi]},{v,0,2 \[Pi]},ViewPoint->{4,-4,8}]
> My scaling and unscaling utilities need the maximum and minimum coordinat=
es as inputs
> squeeze[x_,min_,max_]:==(x-min)/(max-min)
> unsqueeze[fx_,min_,max_]:==fx (max-min)+min
> Now I can get an list with each pixel's {x,y,z} as
> xyz==Map[unsqueeze[#,-1,1]&,ImageData[Image[ParametricPlot3D[ff[u,v],{u,0=
, 2\[Pi]},{v,-\[Pi]/2,\[Pi]/2},
> ColorFunction->Function[{x,y,z},Glow[RGBColor[squeeze[x,-1,1],squeeze[y,-=
1, 1],squeeze[z,-1,1]]]],
> ColorFunctionScaling->False,ViewPoint->{4,-4,8},Mesh->False,Boxed->False,=
> Now, for example, you can print the pixel coordinates or  view the points=
 in 3D with a function like
> Graphics3D[Map[{Hue[(#[[3]]+1)/2],Point[#]} &,xyz[[ ;; ;;10, ;; ;;10,All]=
> My question is if there is a method for Graphics3D which can recover pixe=
l coordinates with a similar result?
> Thank you,
> Russell Chipman

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