Identify the point where three lines are meeting, thus making a Y section.

This is the structure , in this the pink lined part is the Y section.

We need to find the points where this Y section is formed. Also we may adress this as finding or identifying the point where three sides are intersecting.

[Dyuman Joshi]

How exactly is this problem related to MATLAB?

[Nupur]

We need to use MATLAB to find this. I used in my previous code the unique inbuilt function of MATLAB, but it didnt go as well.. So we need to develop another logic for this now.

Please feel free to ask if not understood.

[Dyuman Joshi]

Please share your previous code.

Also, what is input you have to work with? Is it just this figure? Or do you have some sort of data?

[Nupur]

We have node cooridnates

[Nupur]

Also if we use triangulation , then how to differentiate between upsidedown Y and normal Y?

Answer 1

[Matt J]

Use delaunay to form the delaunay triangulation and then freeBoundary to find which vertices are on the boundary. The vertices that are not on the boundary will be the 3-way intersections.

T=delaunay(allVertices);

[~,boundaryVertices]=freeBoundary(T);

intersections=setdiff(allVertices,boundaryVertices,'rows')  %all points minus boundary points

[Nupur]

Could you please tell the size of allVertices matrix?

I am working only with x and y coordinates, so should it be a matrix wiht 2 columns?

The below is my matrix which can pe put as allVertices:

hexagon =

2.0784 8.5300

0 9.7300

-2.0784 8.5300

-2.0784 6.1300

0 4.9300

2.0784 6.1300

8.4264 4.8650

6.3480 6.0650

4.2696 4.8650

4.2696 2.4650

6.3480 1.2650

8.4264 2.4650

I got this error actually :

Incorrect number or types of inputs or outputs for function 'freeBoundary'.

[Dyuman Joshi]

Use delaunayTriangulation instead of delaunay

hex = [    2.0784    8.5300
         0    9.7300
   -2.0784    8.5300
   -2.0784    6.1300
         0    4.9300
    2.0784    6.1300
    8.4264    4.8650
    6.3480    6.0650
    4.2696    4.8650
    4.2696    2.4650
    6.3480    1.2650
    8.4264    2.4650];
    
T=delaunayTriangulation(hex(:,1),hex(:,2));
[~,boundaryVertices]=freeBoundary(T);
intersections=setdiff(hex,boundaryVertices,'rows');  %all points minus boundary points

%plotting all vertices
scatter(hex(:,1),hex(:,2),'r*')
hold on
%plotting vertices at boundaries
scatter(intersections(:,1),intersections(:,2),'bo')

[Nupur]

Error in setdiff (line 163)

[varargout{1:nlhs}] = setdiffR2012a(varargin{1:2},logical(flaginds(1:3)));

Getting this error using setdiff

[Dyuman Joshi]

Why is there R2012a in between???

And it's not clear how exactly are you using variables as inputs.

[Nupur]

Sorry,error cleared. Was due to online version.

thanks!

[Nupur]

However, the triangulation isnt working properly at these vertices:

Refer this figure, it should identfiy that Y

[Matt J]

I don't know how you mean for us to interpret your figure. It doesn't look like the figure in your original post, and you now have both red and blue connections.

[Nupur]

yes,

I thought it should identify any such three way sections thoughout the structure.