$collisionmodel

The QC command $collisionmodel is used to embed a non-animated collision mesh in a model, for use in VPhysics calculations.

Tip:Use vcollide_wireframe 1 to view collision meshes in-game.

Tip:If your model has moving parts that need to collide, including ragdoll limbs, use $collisionjoints.

Warning:Collision meshes should be extremely low-poly in comparison to body meshes, and even lod meshes. See collision mesh.

Usage

$collisionmodel <collision mesh SMD>
{
    <options>
}

$mass <float|kilograms>: Manually set the mass of the model.; Todo: Presumably this has some use outside physics simulation?
$automass: Automatically compute the mass of the model. The calculation takes into account the density/thickness of the material defined by $surfaceprop and/or prop_data, as well as the volume of the collision SMD itself.
$concave: A collision model must be a convex shape, but you can create concave shapes by including multiple meshes in the same model. $concave tells studiomdl that this is what you want it to do, rather than make a single convex hull by bridging any gaps.
$maxconvexpieces <int>: By default, studiomdl limits a concave collision model to twenty convex pieces. This command can be used to override the limit - for instance if you are creating an unusually large model.; Note:Introduced with the Orange Box. In the Ep1 engine, run studiomdl with -fullcollide when compiling instead.
$masscenter <Vector|offset>: Override the center of mass, in local coords.
$inertia <int|scale>: Inertia scale.
$damping <int|scale>: Linear damping scale.
$rotdamping <int|scale>: Rotational damping scale.
$drag <int|scale>: Scales air resistance.

$collisionmodel "tree_deciduous_01a_physbox.smd"
{
	$mass 350.0
	$concave
}