[Gmsh] Use physical Groups after boolean operations

[Christophe Geuzaine]

> On 28 May 2018, at 14:27, Leonardo Roncetti <leonardo at techcon.eng.br> wrote:
> 
> I am doing all the geometry by programming and using GUI only to see results. Suppose that I create 2 surfaces that intersect each other. I define a physical group “vertical” for surface {1} and “horizontal” for surface {2}. As they intersect each other, I use “Coherence” or Boolean operation to remove duplicate areas. But when I do this I lose the references of original surfaces, because I have now 3 surfaces and not necessary surface “horizontal” is {1}.

Indeed.

> Actually, I have hundred of surfaces and cannot do it “by hand”.
> In suma: How can define physical groups than use coherence and keep the defined physical groups?    

Currently the "intelligence" of our tagging is limited to cases where an entity is transformed into a single entity during boolean operations. We plan to improve this in the future, but OpenCASCADE is still a bit buggy at the moment when asked to identify the ancestry of shapes across operations, which is necessary for fully automatic tagging to work.

Until then, here are two possibilities to automate the tagging:

1) create the shapes in such a way that the "Coherence" operation actually only glues shapes together at the very end. This way each shape is transformed into a new one (albeit with modified boundary). The tags will be preserved.

2) tag the shapes geometrically with the BoundingBox queries.

Christophe

>  
> Best Regards,
> Leonardo.
>  
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Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine

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