Get vertices that create surface mesh from trisurf

Hi,

I am trying to obtain the vertices on the surface of my triangulated mesh only. So far, I have managed to create the mesh and plot it using the following code:

tri = triangulation(T, P);
tMesh= trisurf(tri,'Facecolor','red','FaceAlpha',.1,'EdgeColor','red');

where:

• T = Triangulation connectivity list, specified as an m-by-n matrix, where m is the number of triangles or tetrahedra, and n is the number of vertices per triangle or tetrahedron. Each row of T contains the vertex IDs that define a triangle or tetrahedron.
• P = Points, specified as a matrix whose columns are the x-coordinates, y-coordinates, and (possibly) z-coordinates of the triangulation points. The row numbers of P are the vertex IDs in the triangulation.

Is there anyway I can obtain the vertices which 'trisurf' uses to produce the triangulated surface mesh? Otherwise, is there an alternative way I can find the surface vertices?

Any help would be greatly appreciated!

Thank you kindly.

Answer 1

[DGM]

It really sounds like this question isn't the question that's been asked.

You don't need to get the vertices from trisurf(), because it doesn't "produce" them. You have the vertices to begin with.

% you already have this
F = [1 2 3; 2 1 4; 5 6 7; 2 6 5; 4 6 2; 6 4 8; 9 5 7; 
    5 9 10; 11 9 12; 9 11 10; 10 2 5; 2 10 3; 11 13 10; 
    11 14 13; 14 1 15; 1 14 11; 16 10 13; 15 10 16; 15 3 10; 
    3 15 1; 4 17 8; 1 17 4; 11 17 1; 17 11 12; 6 18 15; 
    8 18 6; 18 8 17; 15 18 14; 19 9 20; 9 19 12; 17 19 18; 
    19 17 12; 6 20 7; 15 20 6; 20 15 16; 7 20 9; 13 20 16; 
    20 13 19; 13 18 19; 18 13 14];
V = [-0.5 -0.5 -0.5; -0.5 0.5 0.5; -0.5 0.5 -0.5; -0.5 -0.5 0.5; 
    0.5 0.5 0.5; -0.25 0.25 0.5; 0.5 0.25 0.5; -0.25 -0.5 0.5; 
    0.5 0.25 0; 0.5 0.5 -0.5; 0.5 -0.5 -0.5; 0.5 -0.5 0; 
    0.25 -0.25 -0.5; -0.25 -0.25 -0.5; -0.25 0.25 -0.5; 0.25 0.25 -0.5; 
    -0.25 -0.5 0; -0.25 -0.25 0; 0.25 -0.25 0; 0.25 0.25 0];

% then you put it in a triangulation object
T = triangulation(F,V);

% then you put it in a patch object
hp = trisurf(T,'Facecolor','red','FaceAlpha',0.1,'EdgeColor','k');

% they are all the exact same data you started with
% because that's what you put in them
[isequal(F,T.ConnectivityList) isequal(F,hp.Faces)] % faces

ans = 1×2 logical array
   1   1

[isequal(V,T.Points) isequal(V,hp.Vertices)] % vertices

ans = 1×2 logical array
   1   1

I don't get it.

I'll note the phrase "surface vertices". If this were about finding the boundary of a tetrahedral mesh, maybe that's a thing, but it's clearly not a tetrahedral mesh. If this were about finding and removing interior faces/vertices, then maybe that's a good question, but now I'm guessing about something which was never asked about a model which was never shown.