/*!

\page about_meshes_page About meshes

\n \b MESH represents a discretization of a geometrical CAD model into
a set of entities with a simple topology. 

It is possible to \subpage constructing_meshes_page "construct meshes" 
on the basis of geometrical shapes produced in the GEOM module.
Construction of \subpage constructing_submeshes_page "sub-meshes"
allows to mesh parts of the geometrical object, for example a face,
with different meshing parameters or using another meshing algorithm
than other parts.

3D mesh can be generated basing on a 2D closed mesh.

Several created meshes can be \subpage building_compounds_page "combined into another mesh".

The whole mesh or its part can be \subpage copy_mesh_page "copied" into another mesh.

Meshing parameters of meshes and sub-meshes can be 
\subpage editing_meshes_page "edited", then only the mesh part
depending on the changed parameters will be re-computed.

Meshes can be edited using the MESH functions destined for 
\ref modifying_meshes_page "modification" of generated meshes.

Meshes are stored in DAT, MED, UNV, STL, CGNS, GMF and SAUVE formats and can be
\subpage importing_exporting_meshes_page "imported from and exported to"
 the file in these formats.

The \b topology of a mesh is described by the relationships between its
entities including:

<ul>
<li>\b Node &mdash; 0D object of a mesh presented by a point with coordinates (x, y, z).</li>
<li>\b 0D element &mdash; element of a mesh defined by one node.</li>
<li>\b Edge &mdash; 1D element of a mesh defined by two nodes.</li>
<li>\b Face &mdash; 2D element of a mesh defined by three or four edges (closed contour).</li>
<li>\b Volume &mdash; 3D element of a mesh defined by several faces.</li>
<li>\b Ball element &mdash; discrete element of a mesh defined by a node and a diameter.</li>
</ul>

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;These entities are
considered as topological entities and they don't
imply any geometric representation. Only \b Nodes reference  geometric
representations of points with definite coordinates. The node entity
contains  additional information about its position in the space
and its relations with the meshed CAD model. Its position could be
described in the following way:

<ul>
<li><b>3D position</b>. It characterizes the position of a node in a
  solid geometry and is defined by three coordinates x,y and z and a
  reference to the solid geometrical entity. </li>
<li><b>Surface position</b>. It characterizes the position of a node on a
  geometric surface and is defined by the u,v position in the parametric
  space of the corresponding surface.</li>
<li><b>Line position</b>. It characterizes the position of a node on a
  geometric curve and is defined by the u parameter and the
  corresponding curve.</li>
<li><b>Vertex position</b>. It characterizes the position of a node on a
  geometric point of the meshed CAD model and is defined by the x,y,z
  coordinates of the corresponding vertex.</li>
</ul>

*/