POV-Ray Geometric Shapes

smooth_triangle{ ...} - flat triangle shape with modified surface normals
to simulate a smooth surface and hide the sharp-edged seams between individual triangles in meshes of triangles.

built-in shape, non-CSG

//Syntax: ------------------------------
smooth_triangle{ <vertex_1>,<normal_1>,
                 <vertex_2>,<normal_2>,
                 <vertex_3>,<normal_3>,
               } //---------------------

Beispiel:

// -------------------------------------------
smooth_triangle{
  // vertex vector, surface normal vector
  < 0.00, 0.00, 0.00>,<-0.55, -0.55, -1.00>,
  < 3.00, 0.00, 0.00>,<-0.75,  0.75, -1.00>,
  < 0.00, 2.00, 0.00>,< 0.75, -0.75, -1.00>
  texture{ pigment{ color rgb<1,1,1>}
           finish { phong 1}
         } // end of texture
  scale <1,1,1>
  rotate<0,0,0>
  translate<0,0,0>
} // end of smooth_triangle -----

Note: "triangle" and "smooth_triangle" are used normally to build all those objects which are too complex to be made by built-in shapes. They are usually not created by hand but are converted from other files (i.e. files which use HF_macros with file output) or generated by utilities(i.e. POV_Tree + TOM_TREE for trees, Poser + converter PoseRay for human and animal creatures etc. )
See also: mesh and mesh2.