# How to find all facets with thickness < 0.5 mm and paint red color

Hi All,

I am new with Babylon JS, I am starting a project that it will load a 3D model (.obj file) and paint red color to all facets with thickness < 0.5 mm.

I can find out all vertices and indices as follow:
mesh.getVerticesData
mesh.getIndices

and get all facets (triangles). So next step, I will need to measure thickness on each facet and paint red color to.

I am not sure how to measure them, it can be related to Ray ??? Can everyone help me to find out

Thanks,
Phu

Welcome aboard!

What do you call the thickness of a triangle? It is a flat polygon, so its thickness is 0(?)

As my know that objects are from BJS built by facets (triangles). A basic box will be drawn by 12 triangles.
So this is case, I want to measure thickness of the box. And more general, objects will be loaded by *.obj file.

Still, I donâ€™t understand, how do you define the thickness of this:

https://playground.babylonjs.com/#BCU1XR#0

Some 3D printers canâ€™t print some details which are less than 0.5mm, so I will check thickness of all details on model. In this case, maybe fingers in your example have less than 0.5mm and I will paint them in red color for warning.

Ok, I understand better.

So I think you need to find for each vertex of a triangle which is the nearest triangle that intersects the line going from this vertex in the direction of the inverse (opposite, meaning -normal) of the normal to this vertex (I donâ€™t know if this algorithm will work in all cases)â€¦

You can use the `Ray` class to compute the intersection of a line with the triangles of a mesh (donâ€™t forget to exclude the source triangle from the computation!).

Thanks @Evgeni_Popov

I have created an example on Playground at
https://playground.babylonjs.com/#ZMTZ0Q#1

I tried to create multi rays with inverse of direction and intersect with box, how can I exclude source triangle and will get value on second intersection.

Currently, ray.distance always 0 because the ray intersect with source triangle.

The easiest way is to move a little bit `pos` in the negative normal direction:

https://playground.babylonjs.com/#ZMTZ0Q#3

A better way would be to get all intersections, sort them and take the first one with a non 0 distance, but thereâ€™s currently no way to retrieve all intersections of a ray with a mesh.

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Moving a little bit â€śposâ€ť is ok for me, I see that it works on my side. Thanks for your help @Evgeni_Popov