[Feature]: Env-wise gravity vector

[nootnootpengupengu]

What feature or enhancement are you proposing?

The ability to set a unique gravity vector for each of my simulation environments, not a global vector for all envs.

Motivation

Part of my domain randomization scheme requires varying the gravity vector between all envs during intraining. It is currently not possible to do so as it's a global parameter in SimOptions.

Potential Benefit

Improved policy training and robustness due to increased resilience from different gravity force.

What is the expected outcome of the implementation work?

The ability to set a SimOptions.gravity = gravity_tensor, where gravity_tensor.shape = (num_envs, 3)

Additional information

No response

[bb7332193]

This would be very useful, would a Turbulence Field work for this purpose? Not sure if the turbulence experienced by each environment would be different. I'm hoping it is different.

There is also scene.sim.rigid_solver.apply_links_external_force(...) which might work, although it does not seem to be documented.

[Milotrince]

PR #1324 added this, but there is a bug. I will fix this.