Hello,
for some time we’ve been getting reports of rare collisions in some parts of our maps (we are developing a Bus Simulation Game collisions are between bus and ground).
I’ve recently found a somewhat consistent way to reproduce the issue and recorded it with the Chaos Visual Debugger.
Unfortunately the debugger did not bring the expected clarity. The collision appears to happen outside the bounds of the mesh.
I’ve attached the CVD Recording. The collision can be seen at frame 315 between BP_VDL_Citea and the ground.
We’re looking for any way to debug this issue further or any changes that we could backport to fix the issue.
Regards,
Max
Hi Max,
Thank you for the Chaos trace, that will help a lot! I have taken a quick initial look at this, and as you say the physics is telling us that it hits the kerb in frame 315. As to why it does this without actually hitting the geometry, there are a couple of reasons, but it could be that the geometry is getting inflated for some reason within the config. This is getting inflated quite a lot though in this case if that is what is causing it.
I’ll take a deeper look into this shortly, and find out if there is a good way of confirming this - and if so how we reduce the expansion size.
Best
Geoff
Hi Max, if you take a look at the collision detail box, there is a surprisingly large collision margin there which may explain the unusual collisions.
[Image Removed]You can alter this in the Project settings in the picture below. Clipping the max to a different limit, or altering the multiplier are the usual options here.
If you can do this and check if it solves your issue that’d be great, otherwise we can look into enabling some other debug draw for this area which aren’t actually in CVD yet.
All the best
Geoff
Hi Geoff, thanks for the help.
I’ve done some testing by setting “p.Chaos.Collision.MarginMax” to 0 before spawning the vehicle.
Unfortunately that does not seem to have made a difference. The collision still happens.
I’ve attached a new recording, collision at 297.
Regards,
Max
PS: Image of the project settings you wanted to attach seems to be missing.
Hi Max,
Yep, I can see that, and can confirm that the collision margin in that collsion has been reduced to 0
[Image Removed]There are 2 more things which are potentially the cause.
1) From the picture above which shows the problem collision, that Collision Tolerance number is pretty high. There are a number of params for this one, but if you try:
p.Chaos.Collision.Manifold.MatchPositionTolerance
p.Chaos.Collision.Manifold.MatchNormalTolerance
to begin with.
2) Looking closely there are some very, very narrow and long triangles on that asset. Shapes like those are notorious for causing numerical tolerance issues on games. If you can remove those and see if this problem still happens that may also yield the answer.
All the best
Geoff