[OVPHYSX] Support for rough terrain locomotion

[AntoineRichard]

Summary

Enable rough terrain locomotion tasks to run on the OVPhysX backend. Integration task — validates that Articulation, ContactSensor, and terrain generation work together for legged locomotion.

Target environments:

• `Isaac-Velocity-Flat-Anymal-C-Direct-v0` (flat terrain, simpler)
• `Isaac-Velocity-Rough-Anymal-C-Direct-v0` (rough terrain, full validation)

What Needs to Work

1. Robot spawning and cloning (Anymal C articulation)
2. Joint control via actuators
3. Contact detection (foot contacts for gait rewards)
4. State observations (joint pos/vel, root state, projected gravity)
5. Episode resets
6. Terrain mesh loading (height field / trimesh from USD)
7. Scene queries (ray casts for height scanning) — may be blocked

OVPhysX Questions for @marcodiiga

1. Does ovphysx support loading trimesh collision geometry from USD?
2. Does ovphysx support GPU scene queries (ray casts)?

Dependencies

• Critical: ContactSensor ([OVPHYSX] ContactSensor #5325) — blocks gait rewards
• Requires Articulation (PR ovphysx backend integration #4852, done)
• May require scene query API from ovphysx

Spec

Full design spec: `docs/superpowers/specs/2026-04-20-ovphysx-rough-terrain-locomotion-design.md`

Parent issue: #5315

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📋 Full Design Spec (click to expand)

OVPhysX Rough Terrain Locomotion Support — Design Spec

Issue: #5321 — [OVPHYSX] Support for rough terrain locomotion
Date: 2026-04-20
Status: Draft

Summary

Enable rough terrain locomotion tasks to run on the OVPhysX backend. This is an integration task, not a new implementation — it validates that the core backend components (Articulation, ContactSensor, terrain generation) work together correctly for legged locomotion.

Target environments:

• Isaac-Velocity-Flat-Anymal-C-Direct-v0 (flat terrain, simpler)
• Isaac-Velocity-Rough-Anymal-C-Direct-v0 (rough terrain, full validation)
• Manager-based velocity tracking tasks with various robots (Anymal, Unitree, etc.)

Prerequisites

This task depends on several other OVPhysX components being complete:

Component	Issue	Status	Required For
Articulation	PR #4852	Done	Robot control
ContactSensor	New issue	Needed	Foot contact detection
RigidObject	#5316	Needed	Terrain objects (if any)
SceneDataProvider	New issue	Nice-to-have	Visualization

ContactSensor is the critical dependency. Without it, locomotion tasks cannot detect foot contacts for gait rewards.

What Needs to Work

Flat terrain (minimum viable)

1. Robot spawning and cloning — Anymal C articulation across N environments
2. Joint control — Position/velocity targets via actuators
3. Contact detection — Foot contact forces for gait rewards
4. State observations — Joint positions/velocities, root state, projected gravity
5. Episode resets — Root state write-back on termination

Rough terrain (full validation)

All of the above plus:

6. Terrain generation — Height field or trimesh terrain
7. Terrain-aware spawning — Robots placed on valid terrain locations
8. Height scanning — Ray-cast or height-field queries for terrain observations

Potential Blockers

Terrain mesh loading: OVPhysX loads from USD. If terrain is generated procedurally (height field → USD mesh), verify the pipeline works without Kit:

• isaaclab.terrains generates meshes and writes them to USD
• OVPhysX must load these meshes from the exported USD

Scene queries (ray casts): Some locomotion tasks use height scanning via ray casts. If ovphysx lacks scene query APIs, this feature is blocked. Check with @marcodiiga.

Question for @marcodiiga: Does ovphysx support:

1. Loading trimesh collision geometry from USD?
2. GPU scene queries (ray casts)?

Implementation Steps

1. Start with flat terrain — verify Anymal C walks on flat ground
2. Add terrain meshes — verify procedural terrain loads in ovphysx
3. Validate full rough terrain — run the complete velocity tracking task
4. Profile performance — compare step time vs PhysX backend

Task Configuration Changes

Create OVPhysX-specific task configs (or verify existing ones work):

# Flat terrain with OVPhysX
@configclass
class AnymalCFlatOvPhysxEnvCfg(AnymalCFlatEnvCfg):
    sim: SimulationCfg = SimulationCfg(
        physics_cfg=OvPhysxCfg(...)
    )

The environment logic itself should not change — only the physics backend config.

Validation

Flat terrain validation

./isaaclab.sh -p source/isaaclab_tasks/isaaclab_tasks/direct/anymal_c/anymal_c_env.py \
    --num_envs 4 --task Isaac-Velocity-Flat-Anymal-C-Direct-v0

Rough terrain validation

./isaaclab.sh -p source/isaaclab_tasks/isaaclab_tasks/direct/anymal_c/anymal_c_env.py \
    --num_envs 4 --task Isaac-Velocity-Rough-Anymal-C-Direct-v0

Training validation

Run 10K steps of training and verify:

• Reward increases over time (learning signal exists)
• No NaN/inf in observations or rewards
• Episode resets work correctly
• Performance within 2x of PhysX for equivalent env count

Dependencies

• Requires ContactSensor (blocks gait rewards)
• Requires Articulation (PR ovphysx backend integration #4852, done)
• May require scene query API from ovphysx for height scanning
• May require terrain mesh loading verification

Estimated Scope

• OVPhysX task config files: ~50 lines each
• Bug fixes in OVPhysX components: variable (discovered during integration)
• No new core implementation — this is an integration/validation task