Wolfram Technology Guide: Integrated Geometric Computing  previous | next 
Use Arbitrary Implicit Regions to Visualize Surfaces
Mathematica allows you to select arbitrary regions with implicit specifications, to emphasize particular features in surfaces.
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Click for copyable input
ParametricPlot3D[{1.13^

   v Cos[v] (1 + Cos[u]), -1.13^v Sin[v] (1 + Cos[u]), -1.4 1.13^

   v (1 + Sin[u])}, {u, 0, 2 Pi}, {v, -15, 6}, PlotRange -> All, 

 MeshFunctions -> {(#1^2 + #2^2 - 5 &)}, Mesh -> {{0}}, 

 MeshShading -> {Opacity[.4, Yellow], Red}, MaxRecursion -> 4, 

 Axes -> None]
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