[Gmsh] Problem using stl data as holes in volumes.

Topology Pathway topology.pathway at yahoo.com
Mon Jan 15 19:06:49 CET 2018

 Hello Gmsh-Team:
I am trying to mesh a volume with a hole in it.  The outer surface-loop is
a box built using OpenCascade and the inner 'hole' is a surface-loop from an stl file (see attachment 1).
The geo script is given by:
###### begin script ######Merge "merge_vtk_test_vein_test_vol.stl";SetFactory("OpenCASCADE");
Box(2) = {10, 10, 20, 35, 30, 20};
Surface Loop(2) = {6, 2, 4, 3, 7, 5};  // box surface-loop
Surface Loop(3) = {1};  // stl object surface-loop
Volume(3) = {2, 3};###### end script ########
The commands following the Box command (comments mine) were generated using the Geom..->Elem..Ent..->Add->Volume 
tool using the box as the outer surface-loop and the stl object as the inner surface-loop.
When I try to mesh this volume in 3D (Mesh->Define->3D) it only meshes the volume of the outer 
surface-loop and ignores the inner 'stl based' surface loop.  Verified using clipping tool.
I have tried this with two extruded boxes and can get it to work fine (see attachment 2).
Also, if I just load the stl file and build a volume (using only the stl surface with no holes) the interior
of this stl volume is meshed with 3d tets.  The problem seems to be related to the use of the stl surface as a hole.
 I am using gmsh version 3.0.5.
Tony M.
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