pointLocation return only one ID if a point lies in more than one triangle

Hi everyone,

this is my code in which I've two triangles and one point and I want to check in which triangle my point lies (I've to use pointLocation for more complex case like a mesh of STL file).

clear all

points=[0 0;1 0; 0 1; 1 1];
tri=[1 2 3; 1 2 4];

TR=triangulation(tri,points);
triplot(TR);
check=[0.6 0.2];
hold on
plot(check(1,1),check(1,2),'o');

ID = pointLocation(TR,check);

I'd like to be returned both the ID of the triangles in which the point lies. How can I do?

Answer 1

[VINAYAK LUHA]

Hi Matteo,

I understand that you want to find the IDs of all triangles which enclose a point.The “pointLocation” function returns the triangle ID of only the first enclosing triangle as defined in the “Triangulation connectivity”.

To get triangleIDs of all the enclosing triangles, you can do a linear search over all the triangles and register the ones which enclose the given point.

The code snippet to achieve this can be seen below:

points = [0 0; 1 0; 0 1; 1 1];
tri = [1 2 3; 1 2 4];
check = [0.6 0.2];
plot(check(1,1), check(1,2), 'o');
hold on
enclosingTriangleIDs = [];
for i = 1:size(tri, 1)
    TR = triangulation(tri(i,:), points);
    ID = pointLocation(TR, check);
    if ~isnan(ID) 
        enclosingTriangleIDs = [enclosingTriangleIDs, i];
    end
    triplot(TR);
end
disp("IDs of triangles enclosing the point:");
disp(enclosingTriangleIDs);
hold off

To learn more about “traingulation” and “pointLocation”, you may refer to the MathWorks documentation links below:

1. https://in.mathworks.com/help/matlab/ref/triangulation.html
2. https://in.mathworks.com/help/matlab/ref/triangulation.pointlocation.html

Hope this helps.

Regards,

Vinayak Luha