3D Printing... STL files!

[Cableguy]

Hi guys...

As a second part of my 3D printing related post, I am seeking information about STL files...

I understand they list a series of triangles, but what I can't understand is how they relate to each other...
Are they relative coordinates or absolute?
Relative, to what?
Can any one give an example on how 2 or 3 triangles relate to each other?

 

[sorex]

you have vertices which are individual points in an x/y/z 'world'.

a (triangular) face consists of 3 vertices.

something like (see it is 2 closed triangles )

/_\
\ /

are sharing the same vertices at the left/right of the dash (-) and the top of the ^ and bottom of the v

so that file probably consists of a list of vertices and face data.

 

[Cableguy]

So if I understand right, they are absolute coordinates, and a "shared" face will have two points (out of three) in common.

 

[sorex]

it could be one aswell. It depends if the shape is open or not.

here's an example...

look at the ? face. it could have 3 shared ones but it doesn't. why not? because you don't need it because it's a white face on a white background
so optimize wise you don't need to recalculate and draw it's face and vertices.

actually you can double the values. the 2 visible shared points are actually 4 times the same vertice

 

[sorex]

https://en.wikipedia.org/wiki/STL_(file_format)

 

[Cableguy]

Thanks @sorex, I had been there myself, but looking at a real stl file made no sense to me so I decided to ask the real experts