What is the reason for the 0.04 margin?

[dimforge]

What is the reason for the 0.04 margin?

[sebcrozet]

Collision margins improve dramatically collision detection times and accuracy by allowing the use of distance computation algorithms to compute penetration depths. Also, by smoothing rough edges, it helps reduce simulation artifacts due to the discrete nature of the geometric models.

The use of margins (and thus a pre-erosion of geometric models) is common on most physics engines I know (Box2D, Bullet) and even proprietary engines that attempt to be more realistic for engineering purposes.

The exact value 0.04 is kind of arbitrary though. It cannot be changed by the user yet but will in the future.

[MovingtoMars]

Couldn't the margin be automatically deducted off of the shape dimensions, so the output is what's expected?

[sebcrozet]

Not really. This could be done for some specific shapes like boxes and balls (which is what Bullet does), but for other shapes it might lead to unwanted results. For example auto-eroding a triangle mesh might cause self-intersections on thin parts.