FEM MeshGmshFromShape

Description
For a finite elements analysis the geometry needs to be discretized into a FEM Mesh. This command uses gmsh (which needs to be installed on the system) for calculating the mesh.

Usage

 * 1) Select the shape you want to analyze. For volume FEM this needs to be a solid or compsolid. A compsolid is necessary if your part is made from multiple materials. (A compsolid can be created with the BooleanFragments command.) -- For shell and beam FEM somebody needs to fill in the details here.
 * 2) There are several ways to invoke the command:
 * 3) * Press the button.
 * 4) * Select the option from the menu.
 * 5) Optionally edit the minimal and maximal element size. (Autodetection works fine unless you apply complicated boundary conditions.)
 * 6) Click the  button and wait for the computation of the mesh to complete
 * 7) Close the task. You now should see a new FEMMeshGMSH object in your active analysis container.

Nonpositive jacobians

 * https://forum.freecadweb.org/viewtopic.php?f=18&t=16017&start=20#p485789