\page prism_3d_algo_page 3D extrusion meshing algorithm
-3D extrusion algorithm can be used for meshing prisms, i.e. <b>3D Shapes</b>
+3D extrusion algorithm can be used for meshing prisms, i.e. 3D shapes
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.
+edges. 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.
+The prism is allowed to have sides composed of several faces. (A prism
+side is a row of faces (or one face) connecting the corresponding edges of
+the top and base faces). However, a prism
+side can be split only vertically as indicated in the
+picture below.
-\image html image157.gif "Prism with 3D extrusion meshing".
+\image html prism_ok_ko.png "A suitable and an unsuitable prism"
+In this picture, the left prism is suitable for meshing with 3D
+extrusion algorithm: it has six sides, two of which are split
+vertically. The right prism cannot be meshed with this
+algorithm because one of the prism sides is split horizontally (the
+splitting edge is highlighted).
-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.
+The algorithm can propagate 2D mesh not only between horizontal
+(i.e. base and top) faces of one prism but also between faces of prisms
+organized in a stack and between stacks sharing prism sides.
-\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.
+\image html prism_stack.png "Prism stacks"
+This picture shows four neighboring prism stacks, each comprising two prisms.
+The shown sub-mesh is used by the algorithm to mesh
+all eight prisms in the stacks.
+
+To use <em>3D extrusion</em> algorithm you need to assign algorithms
+and hypotheses of lower dimensions as follows.
+(A sample picture below shows algorithms and hypotheses used to
+mesh a cylinder with prismatic volumes).
+
+\image html prism_needs_hyps.png
+
+The \b Global algorithms and hypotheses to be chosen at
+\ref create_mesh_anchor "Creation of a mesh object" are:
+<ul>
+<li> 1D algorithm and hypothesis that will be applied for meshing
+ (logically) vertical edges of the prism (which connect the top and the
+ base faces of the prism). In the sample picture above these are
+ "Regular_1D" algorithm and "Nb. Segments_1" hypothesis.</li>
+</ul>
+
+The \b Local algorithms and hypotheses to be chosen at
+\ref constructing_submeshes_page "Construction of sub-meshes" are:
+<ul>
+ <li> 1D and 2D algorithms and hypotheses that will be applied for
+ meshing the top and the base prism faces. These faces can be meshed
+ with any type of 2D elements: quadrangles, triangles, polygons or
+ their mix. It is enough to define a sub-mesh on either the top or the base
+ face. In the sample picture above, "BLSURF" algorithm meshes
+ "Face_1" base surface with triangles. (1D algorithm is not
+ assigned as "BLSURF" does not require divided edges to create a 2D mesh.)
+ </li>
+ <li> Optionally you can define a 1D sub-mesh on some vertical edges
+ of stacked prisms, which will override the global 1D hypothesis mentioned
+ above. In the <b>Prism stacks</b> picture, the
+ vertical division is not equidistant on the whole length because
+ a "Number Of Segments" hypothesis with Scale Factor=3 is assigned to
+ the highlighted edge.
+</li></ul>
+
+\image html image157.gif "Prism with 3D extrusion meshing. Vertical division is different on neighbor edges because several local 1D hypotheses are assigned."
+
+\sa a sample TUI Script of
+\ref tui_prism_3d_algo "Use 3D extrusion meshing algorithm".
*/
