Trees and bushes physics

[msobekcz]

Hi all,

I'm about to implement physics for trees and bushes. Mainly for vehicle interaction and wind. At first I though I would add capsules and constraints but based on "SoftBodyCosseratRodConstraintTest" sample, it looks like Cosserat rods are more suitable for this. Is that correct assumption? If so, I have 2 questions:

1. How to handle collisions with vehicle/character? Ideally trunk and branches below certain height would have capsule collisions.

2. Is it possible to compute the constraints in such a way that when simulation starts, the branches maintain their initial position (unless a force is applied)? Basically that the constrains produce forces that exactly compensate for gravity in the initial pose.

Thanks in advance,
Martin

[jrouwe]

1. The cosserat rods don't have volume (they're line segments basically), so if your lower tree branches are thick then it's not a good fit. I would consider the cosserat rods suitable for small bushes / plants etc. You can have a mix of rigid bodies (thick lower branches) and cosserat rods (thin upper branches) but you'll need to manually move the soft body along with your tree and the soft bodies won't affect the motion of the tree which may look weird if the tree topples over and lands on the upper branches.

2. Yes it is possible to do this but it is not simple. I've made an attempt to do this in the hair sim (see here) but it is not working well and I need to refine this. If I get this working then I will make an attempt to provide that functionality for the cosserat rods in the soft bodies too. Bottom line is that when the cosserat rod sim starts it will sag currently. Rigid bodies have the same problem, although you can choose to spawn the tree in a sleeping state so the sagging won't actually happen until you hit it with your vehicle.

[msobekcz]

Thank you very much for both answers. Gives me clear idea of the limitations and where to start!

Have a great weekend,
Martin