[Gmsh] Double surfaces after STEP import

[Negi, Ashish]

Hello Mark and Matthias,

I have been facing the same problem for few months when I import STEP/IGES models created in NX. Your messages here were really helpful to figure out the problem. I downloaded Netgen and found that there are few classes - Partition_Spliter, Partition_Loop3d, Partition_Loop2d, Partition_Loop, Partition_Inter3d and Partition_Inter2d - which remove duplicate topologies and rebuild the solids. 

I included these classes in Microsoft VS project file and replaced original OCC_Internals::healGeometry function. I have not gone through details of how duplicity is being removed, but now my models are being repaired completely in GMSH. 

Regards,
Ashish

-----Original Message-----
From: gmsh-bounces at ace20.montefiore.ulg.ac.be [mailto:gmsh-bounces at ace20.montefiore.ulg.ac.be] On Behalf Of Zenker, Dr. Matthias
Sent: Wednesday, February 09, 2011 9:39 PM
To: Mark van Doesburg; gmsh at geuz.org
Subject: [Gmsh] Double surfaces after STEP import

OK.
In the meantime, we can still use the workaround consisting in "healing" the geometry in netgen, export it to STEP format and import that one with gmsh...

Best regards,

Matthias


-----Ursprüngliche Nachricht-----
Von: Mark van Doesburg [mailto:mark.van.doesburg at technolution.nl] 
Gesendet: Mittwoch, 9. Februar 2011 16:59
An: Zenker, Dr. Matthias; mark.van.doesburg at technolution.nl; gmsh at geuz.org
Betreff: Re: [Gmsh] Double surfaces after STEP import

Hello Matthias,

Thanks for the tip. I've taken a quick look at the code and  it doesn't seem to compute intersections anywhere. Apparently OCC has some functionality to do this by itself... I feel really silly :-(

Unfortunately I also lack the time to work on gmsh. If nobody solves this problem before I start using gmsh again I will have a look at netgen and if it works port the code to gmsh... but I doubt it will happen this year.

regards,

Mark van Doesburg

"Zenker, Dr. Matthias" <Matthias.Zenker at erbe-med.com> wrote:

	Hi Mark,

	just in case you are still interested in that topic:
	I have briefly tried to find out how this is solved in Joachim Schoeberl's netgen. As far as I understand, he uses OpenCascade for his "geometry healing", which i have already used successfully to repair those double surfaces. Looking into the netgen source, there is a method HealGeometry in occgeom.cpp. I don't have the time to delve into the gmsh code an see how this functionality can be incorporated there. But since you have already done gmsh programming, it may be much less effort for you to try this out.

	Best regards,

	Matthias

	-----Ursprüngliche Nachricht-----
	Von: Mark van Doesburg [mailto:mark.van.doesburg at technolution.nl] 
	Gesendet: Montag, 13. September 2010 09:58
	An: Zenker, Dr. Matthias; gmsh at geuz.org
	Betreff: Re: [Gmsh] Double surfaces after STEP import

	Hello Matthias,

	I worked on that code and consider it a complete faillure. In many cases the OpenCASCADE algorithms would not find the intersections. The initial version was quite simple but at some point I started to stack one workaround on top of the other.

	Currently I do not have the time to work on another method, but some algorithms available in CGAL look promising. But in that case I would probably use BRL-CAD to generate the geometry, and importing STEP into BRL-CAD might be sub-optimal.

	regards,

	Mark

	"Zenker, Dr. Matthias" <Matthias.Zenker at erbe-med.de> wrote:

		Hi,

		I have not done FEM calculations for some time (a year or so). The last
		time I did them (using gmsh and Elmer), I had the problem that in
		geometries imported as STEP files (generated by Solidworks), adjacent
		bodies have their own external surface, resulting in double surfaces at
		the interfaces. When I use the mesh generated by gmsh in a FEM
		calculation (I use Elmer), I get no thermal and electrical connection
		because the body meshes are not connected at the interface. There have
		been attempts to clean up double surfaces in gmsh, but I don't know if
		they have come to a success. Could someone of the developpers update me
		on this point?

		Thank you!

		Matthias 

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