[Gmsh] Bug Mesh/Geometry

[Christophe Geuzaine]

Nicolas Tardieu wrote:

> Hi!
> 
> I may have found something weid....
> This geo file represents a prism lying on a cube.
> Let set the value DecalY=0 and mesh it.
> Take a look at the nodes 1 and 24 one the one hand
> and 13 on the other hand : it seems that 2 *mesh* nodes (13 and 31)
> have been merged! But I don't know why!
> Let  set the value DecalY=1.e-3 and mesh it.
> You'll see what I would like to obtain even when DecalY=0 :
> that the nodes 1 and 24, and nodes 13 and 31 aren't merged....
> 

Nicolas - that's due to the way our extrusion algorithm works. In order 
to generate conformal meshes when we extrude different entities (so that 
the meshes match on the boundaries), all the nodes generated by 
extrusion are merged based on their position. The reason why nodes 1 and 
24 are not merged (contrary to nodes 13 and 31) is that they were not 
generated by extrusion...

So I'm not sure if there is a fix for this, or if we actually need one: 
Gmsh actually considers the geometry with DecalY=0 as "degenerated",
since you have an intersection that is not explicitly defined.

Christophe

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