[Gmsh] Labeling the physical entities and extracting nodes on the surface of one physical entity

[Abiti Adili]

Hello,

I am a  new learner of Gmsh. I have  the above attached geometry.geo and omnibus.geo files that  are supposed to create a box mesh with two balls inside. A  cross section of  the box and the labels of the regions is attached above in pdf file.

I am trying to  have 4 different  physical entities which are

1. The first  ball denoted by R.
2. The second ball denoted by P.
3. The complement of  union(R,P) in the box which is  denoted by H.
4. The physical surface which is the boundary of  R.

Upon checking the coordinates of nodes supposedly on the boundary of R, I found that a lot of them are  outside the ball R.

I was wondering if  anyone could help me take a look at the geometry.geo and omnibus.geo and tell me if I have  labelled them correctly so that they correspond to the above 4 entities that I want to have.

Also, how can I extract the indices of nodes on the boundary of R once I have  their coordinates?

Thank you very much.

Adil
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