[Gmsh] New Gmsh release: 1.54

[Christophe Geuzaine]

Hi all -

I've just released a new version of Gmsh (1.54) that fixes a number of
longstanding issues and adds some support for 3D element quality control:

- the discrepancy between the orientation of geometrical surfaces and
   the surface mesh elements has been fixed. You can now ensure that
   the mesh elements are oriented the way you want by simply looking at
   the orientation of the underlying geometrical surfaces. You can of
   course still use Physical Surfaces to modify the orientations a
   posteriori, but in most cases it is not necessary anymore;

- all extrusion commands now return a list of 2 numbers (instead of 1):
   the first, as before, is the number of the "top" of the extruded
   region (i.e., a point for Extrude Point, a line for Extrude Line, a
   surface for Extrude Surface); the second is the number of the "body"
   of the extruded region (i.e., a line for Extrude Point, a surface
   for Extrude Line, a volume for Extrude Surface--see below);

- Extrude Surface now ALWAYS creates a new volume (automatically),
   even when there is no "Layers" specification. This makes it consistent
   with Extrude Point and Extrude Line, which always create new curves
   and surfaces, respectively;

   Warning: you have to modify your old .geo files to avoid duplicate
   volume definitions if you used Extrude Surface without extruding the
   mesh (i.e., without the Layers command). These duplicate volumes
   would be harmless, but they would still screw up your Physical Volume
   definitions later on...

       * Solution 1: use the new volumes (recommended). To do this,
         just remove your old extra volume definitions and let Gmsh
         create the extruded volumes for you. (To retrieve the volume
         number created by Gmsh, use "aa[] = Extrude Surface {...};;":
         the volume number is "aa[1]".)

       * Solution 2: keep the old volumes

         a) clean way: retrieve the new volume number (aa[] = Extrude
            Surface {...};;) and delete the new volume with "Delete {
            Volume aa[1];}"

         b) dirty (but handy) way: since, in order to create the new
            volumes with as few side effects as possible, Gmsh uses
            "low" numbers (actually forcing "Geometry.OldNewreg=0" for
            these volumes), just remove all the "low number" volumes.
            For example, if you have 4 "Extrude Surface" in your file,
            you can just do "Delete{ Volume {1:4}; }"

- the selection of elementary mesh entities generated by extrusion has
   been fixed, and the display of volume mesh elements optimized;

- "smooth" normals are now computed correctly for filled iso-value maps
   as well as for views with custom ranges;

- with the help of Nicolas Tardieu, Netgen (a frontal/Delaunay mesh
   generator written by Joachim Sch\"oberl and released under the
   LGPL--see http://www.hpfem.jku.at/netgen) has been integrated as
   an alternative 3D mesh algorithm. Netgen provides a nice mesh
   optimization module that can be applied to all the tetrahedral
   meshes produced by Gmsh (to improve the quality of the elements).

   Important notes:

       * you should be able apply the mesh optimization on your
         existing geometries without changing anything in the .geo
         files: simply remesh the model and click on the "Optimize
         quality" button (or add "-optimize" on the command line in
         batch mode)

       * BUT, if you want to use Netgen directly for 3D mesh
         generation, beware that it requires all surfaces meshes to be
         oriented with exterior pointing normals. You will have to make
         sure that this is actually the case in your models (Gmsh does
         not enforce this automatically yet), or Netgen WILL fail.

       * all this is still a bit experimental: please send us feedback
         if you encounter bugs!


Downloads, mailing lists, etc.: http://www.geuz.org/gmsh/

Enjoy,

Christophe


New in 1.54: integrated Netgen (3D mesh quality optimization +
alternative 3D algorithm); Extrude Surface now always automatically
creates a new volume (in the same way Extrude Point or Extrude Line
create new lines and surfaces, respectively); fixed UNV output; made
the "Layers" region numbering consistent between lines, surfaces and
volumes; fixed home directory problem on Win98; new
Plugin(CutParametric); the default project file is now created in the
home directory if no current directory is defined (e.g., when
double-clicking on the icon on Windows/MacOS); fixed the discrepancy
between the orientation of geometrical surfaces and the associated
surface meshes; added automatic orientation of surfaces in surface
loops; generalized Plugin(Triangulate) to handle vector and tensor
views; much nicer display of discrete iso-surfaces and custom ranges
using smooth normals; small bug fixes and cleanups.

-- 
Christophe Geuzaine
Applied and Computational Mathematics, Caltech
geuzaine at acm.caltech.edu - http://geuz.org