Reading *.msh files (3D) in Matlab.

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Sanwar Ahmad
Sanwar Ahmad on 1 Oct 2019
Edited: Kazuki Ozawa on 23 Dec 2021
I have created this 3D geometry and the mesh in Gmsh, now I need to get the number of nodes, elements, faces from the mesh in Matlab. How can I do that?
I can send you the *.geo and the *.msh files.
Thanks in advance.
Sanwar

Accepted Answer

ADSW121365
ADSW121365 on 6 Mar 2020
If you're using gmsh, you can use its inbuilt exporter to export a .m file to read into MATLAB.
This loads in a structure array called msh.
Assuming a 3D linear tetrahedral mesh:
%Uses pre-created mesh from gmsh
%Run mesh file name without .m:
Single_coil
nodes = msh.POS';
elements = msh.TETS;
groupsID = elements(:,5);
%If you have multiple domains, this will contain domain IDs
% (assuming you haven't checked 'export all elements', else it will be a column of zeros.
elements = elements(:,1:4);
elements =elements';
geom2 = geometryFromMesh(model,nodes,elements,groupsID); %Import to PDE Toolbox
%If you have subdomains, this will identify their geometries even for a coherent mesh:
%In my example, my actual mesh is just a solid 3D box, however by giving the group IDs
% it is able to identify internal cells, faces etc
%% Plotting:
figure(1); pdeplot3D(model,'FaceAlpha',0.5) %Mesh Plot
figure(2); pdegplot(model,'CellLabels','on','FaceAlpha',0.5) %Geometry
figure(3); pdegplot(model,'FaceLabels','on','FaceAlpha',0.5) %Geometry
%% Finding specific elements/nodes:
%Given this setup, the labels in figures 2 and 3 will allow you to identify faces,
%cells or areas using the usual functions mentioned above.
C_e = findElements(model.Mesh,'region','cell',1); %Coil
C_n = findNodes(model.Mesh,'region','cell',1);
  9 Comments
Kazuki Ozawa
Kazuki Ozawa on 23 Dec 2021
Edited: Kazuki Ozawa on 23 Dec 2021
I appreciate you. And I am glad to hear that Matlab recognise separated cells.
I understand that the procedure of 1. Labelling the cells, 2. Do coherence 3. Meshing and 4. Export without cheking "save all elements" in GMSH.
Lastly, I appreciate you that if you could please provide information of the labelling (like some URL) since official manual doesn't mention how to label the volume very clearly?
Before I asked you, I tried to find the labelling because it looks quite important.
My geometry in GMSH is imported by 3D STEP file from solidworks.
I hope that the labelling function will work the geometry from STEP file as well.
Sincerely

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More Answers (1)

Sahithi Kanumarlapudi
Sahithi Kanumarlapudi on 5 Nov 2019
findElements and findNodes can be used to calculate the number of elements and nodes in a mesh respectievely.
You can find the documentation for both the functions in the following links
  3 Comments
Sanwar Ahmad
Sanwar Ahmad on 24 Sep 2020
@Harshit Ks, follow the link and download gmsh_size_read.m and any related .m files. You may have to change it based on the Gmsh version you are using, that's what I did.
Have fun.

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