Divide square faces into triangles

Hello,

i have a faces matrix and i want to divide it into triangles

e.g. faces is a 100x4 matrix

and i want the same faces as triangles e.g. 123x3 ?

i tried it with the delaunayTriangulation but it distorts my mesh.

thank you

Answer 1

[Matt J]

If the vertices of the squares are all pre-ordered in counter-clockwise or clock-wise order, I think you could just do,

Triangulation=[ Faces(:,[1,2,3])  ;  Faces(:,[3,4,1])] ;

If the vertices are not pre-ordered, it wouldn't be too difficult to loop through and sort them first.

[bbah]

this helped me a lot. thank you

[bbah]

the way you did it i got only Triangulation = [faces(:,1),faces(:,2),faces(:,3)];

i did it with this loop and it works

for i = 1:length(faces)
        first = faces(i,1);
        second = faces(i,2);
        third = faces(i,3);
        fourth = faces(i,4);
        first_lines(i,:) = [first second third];
        second_lines(i+1,:) = [first third fourth];
    end
    second_lines(1,:) = [];
    Triangulation = zeros(2*length(first_lines),3);
    Triangulation(1:2:end-1) = first_lines;
    Triangulation(2:2:end) = second_lines;

[bbah]

OR

first_lines = [faces(:,[1,2,3])];
second_lines = [faces(:,[1,3,4])];
faces = zeros(2*length(first_lines),3);
faces(1:2:end-1) = first_lines;
faces(2:2:end) = second_lines;

Answer 2

[Matt J]

I think you would have to do the following steps in a loop over all the faces,

1. FInd a 2D coordinate system for the plane passing through each face
2. Convert the 3D coordinates of each of the faces vertice to 2D coordinates
3. Do a 2D Delaunay tringulation