Collision detection for low relative velocity, high world velocity rigidbodies

Questions & Answers
1

I am having an issue with collision detection.
This is not a question about high speed objects passing through each other.
This is a question about two objects moving at high speeds in unison, basically two objects that exist in a local frame of reference (say for instance inside an aeroplane). The relative velocity of the two objects is low, with definite frame overlap which would trigger even discreet collision detection. The two colliders are triggers.
However; when the two objects start to move together (the aeroplane starts moving) the collisions become incorrect but predictable. One object has to be moved ahead of the other (in the direction of the planes movement) in order to “collide” leading me to believe that only one object is failing to update correctly, even though in inspection the colliders are in the correct positions.

The objects do not fail to collide, they just collide in the wrong place. Consistently one of the objects has to be ahead of the other, and as the speed increases, this distance ahead must increase to maintain collision detection (using OnTriggerStay).

2

I know your saying they have low relative velocity but i’m not sure they do.

It is dependant on the order of operations which physics performs.

if physics moves all objects, then detects all object collisions your correct, if however it does it on a per object basis where an object moves, does detection, then another object moves, does detection.

There exists only one “local space” and that is on a per object basis.

if your talking about compound colliders for a aircraft simulator though, i think this issue is somehow fixed with fixed joints.

3

For some reason OnTriggerEnter fixes this problem and I still need continuous dynamic collision even though the collisions appear discreet.