What is TriCoord?

Hi, I have a question about Niagara.

From some Niagara examples, I saw “Mesh Tricoord” and used it.

However, even after watching Unreal Engine code, I cannot understand what it is.

What I think is, mesh is a triangle and it has three points(vector 3D) in the world space.

What I found is, TriCoord can be broken to “Tri (int32)” and “bary coord(vector, 3d)”.

I understand bary coord means barycentric coordinate. However…

What is Tri??? Why triangle plane in the 3D world can be represented with one integer and one 3d vector?

Also, I saw some code that make particle’s position with its Tri and Bary coord, (1/3, 1/3, 1/3).

Is each value of Bary coord always between 0 and 1?

Why particle’s position can be represented with one integer and (1/3, 1/3, 1/3)?

Please help me!

you can define a triangle by its surface normal, but each triangle has 3 vertices so the integer is for enumeration 1->3 i think…