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enter image description here

I was working on some geometric manipulation and hoping to further process this graphic's isolines however I was stumped as how best to do that when I looked at the object's GraphicsComplex. I was expecting to see something similar to a question I asked last year about Mesh lines.

c = RevolutionPlot3D[{ x-0.2,-2 x},{x,0.7,1},
  Boxed->False,
  Axes->False,
  Mesh->{8,4}
]
c[[1,1,1,2]]

enter image description here

I'm using Mathematica 12.1 and tired the older function in the other thread too and it returns a similarly confusing GraphicComplex. 5 Dimensional polygons? Lines with one list for it's coordinates? I don't remember how I extracted the isolines.

Can someone describe to me how to extract the Mesh lines from a GraphicsComplex?

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5
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If you just need lines, you can take Normal and extract lines from it:

lines = Cases[Normal[c], _Line, Infinity];

Graphics3D[lines]

mesh lines

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To add to halmir's answer: if you don't need the surface, just use PlotStyle -> None:

RevolutionPlot3D[{x - 0.2, -2 x}, {x, 0.7, 1}, Axes -> None, Boxed -> False,
                 Mesh -> {8, 4}, PlotStyle -> None]

which should give the same picture.

Note that this also includes the setting of BoundaryStyle; if you set it to None, you get this instead:

mesh without boundary

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Another way:

plot /. GraphicsComplex[p_, g_, o___] :> 
  GraphicsComplex[p, Cases[g, _Line, Infinity]]

enter image description here

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    $\begingroup$ ...and one can of course take the complementary approach: DeleteCases[plot, _Polygon, ∞] $\endgroup$ Apr 23 '20 at 0:40

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