Invalid collision / contact from performCollisionDetection & getContactPoints after many createMultiBody / removeBody calls

[manuel-koch]

I'm using pybullet to find collisions / contacts of huge scenes with many thousand bodies ( build from convex OBJ meshes ). I'm not interested in dynamics, I just want to query the "static" scene as-is and find bodies that are in collision in this static state of the scene.

A scene is build by

• adding initial static bodies
• loop
  • adding additional static bodies
  • performing collision detection
  • removing the additional static bodies afterwards

In general this seems to work as expected, but sometimes false collisions / contacts are found between body A & B, i.e. a collision of actually two distinct bodies A & B that are not even touching.

If I try to double check those false collisions by re-building the scene from scratch incl. bodies A & B ( i.e. only adding those bodies that were in the scene when the collision check was done ), I can't find those false collisions anymore, i.e. I get the expected results.

My environment is

• MacOS Ventura 13.4, M1 arm
• Python 3.10.6
• pybullet==3.2.5

Pseudo code of my application:

physics_client = bullet.connect(bullet.DIRECT)

# add many "static" bodies
for i in my_static_bodies:
    collision_shape_id = bullet.createCollisionShape(....)
    bullet.createMultiBody(baseCollisionShapeIndex=collision_shape_id,....)
    
while keep_going:
    # add intermediate "static" bodies
    for i in my_additional_static_bodies:
        collision_shape_id = bullet.createCollisionShape(....)
        bullet.createMultiBody(baseCollisionShapeIndex=collision_shape_id,....)

    bullet.performCollisionDetection(physics_client)
    for contact in bullet.getContactPoints(physicsClientId=physics_client):
        # Handle the colliding bodies doing business logic. Not modifying the bodies in any way.
        #
        # Sometimes false collisions are reported, i.e. reporting bodies in collision that are actually distinct, not even touching.
        # Even the contact points are away from any of the two bodies that are supposedly in collision.

    # remove intermediate "static" bodies
    for i in my_additional_static_bodies:
        bullet.removeBody(....)

Any help / idea appreciated - maybe I'm using pybullet in a way that is wrong or not supported ?