POV-Ray : Documentation : 2.4.2 Finite Patch Primitives
  POV-Ray 3.6 Documentation Online View Torus Bicubic Patch

2.4.2 Finite Patch Primitives

There are six totally thin, finite objects which have no well-defined inside. They are bicubic patch, disc, smooth triangle, triangle, polygon and mesh / mesh2. They may be combined in CSG union but cannot be used in other types of CSG (or inside a clipped_by statement). Because these types are finite POV-Ray can use automatic bounding on them to speed up rendering time. As with all shapes they can be translated, rotated and scaled. Torus Bicubic Patch

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