/*!

\page prism_3d_algo_page 3D extrusion meshing algorithm

3D extrusion algorithm can be used for meshing prisms, i.e. <b>3D Shapes</b>
defined by two opposing faces having the same number of vertices and
edges and meshed using, for example,  the \ref projection_algos_page
"2D Projection" algorithm. These two faces should be connected by
quadrangle "side" faces.

The opposing faces can be meshed with either quadrangles or triangles,
while the side faces should be meshed with quadrangles only.

\image html image157.gif "Prism with 3D extrusion meshing".

As you can see, the <b>3D extrusion</b> algorithm permits to build and to
have in the same 3D mesh such elements as hexahedrons, prisms and
polyhedrons.

\note This algorithm works correctly only if the opposing faces have
the same (or similar) meshing topography. Otherwise, 3D extrusion
algorithm can fail to build mesh volumes.

*/