# Collision in .obj file

I am completely new to Blender and I have never done anything with 3D.

Currently I have some .obj files and I want to understand them. I downloaded source code for a game engine and it's filled with Meshes, so I'm trying to understand how they work and figured this community might help.

So, for example, I have this ground.obj file:

v 1 0 -1
v -1 0 -1
v -1 0 1
v 1 0 1

vt 20 20
vt 0 20
vt 0 0
vt 20 0

f 1 2 3 4
c *


In the game engine, this is a square which the player collides with. If I remove the c *, the player stops colliding with this plane. If I import it into Blender and then export it again, I lose the c *.

In other .obj files, I see a lot of c's as well, below some vectors. What I want to know is how to generate these collisions in Blender so that I get those c's in the .obj file.

Here is a code snippet from another .obj file:

c 17 19 18
c 21 22 23
c 25 26 27
c 29 31 30

v -0.6 0 -1
v -0.6 6 -1
v -0.8 6 -1
c *

v 0.6 0 -1
v 0.6 6 -1
v 0.8 6 -1
c *