material-override

name	material-override
description	Tune PBR metallic / roughness on URDF visual meshes without re-exporting DAE — author an inline `<material_override>` element inside any `<visual>`, and let the engine's URDF→USD pipeline patch the converter's defaults post-conversion. Useful for sim-to-real visual fidelity (DAE materials round-trip poorly; Isaac Sim's importer lands every embedded material at roughness=0.5, metallic=0.0 by default). Trigger: When the user asks to "tune material", "change roughness / metallic", "make the gripper shinier", "fix dull PBR", "override material", "PBR override", or any time the simulator looks washed out after a URDF→USD import.
license	MPL-2.0
metadata	{"author":"genie-sim","version":"1.0"}
prerequisites	["geniesim_ros:build-workspace"]
inputs	[{"name":"urdf_or_xacro_path","desc":"URDF / xacro file containing the `<visual>` to tune","required":true},{"name":"roughness","desc":"PBR roughness 0..1 (omit to leave unchanged)","required":false},{"name":"metallic","desc":"PBR metallic 0..1 (omit to leave unchanged)","required":false}]
outputs	[{"desc":"`<material_override>` element added inside the target `<visual>`; engine regenerates `robot.usda` with patched metallic / roughness on next launch"}]

When to Use

• Robot or asset visual meshes import with washed-out / flat shading after the URDF→USD converter runs.
• User wants to A/B PBR values without re-exporting DAE meshes from Blender / Maya.
• Polishing a robot for sim-to-real visual transfer.
• Author of a new URDF (see add-robot skill) wants the meshes to look right without round-tripping DAE materials.

Do not use for:

• Replacing albedo / textures → must be done in the DAE export.
• Per-prim material at runtime → that's a runtime USD edit, not the <material_override> element.
• Adding a brand-new material — only patches metallic / roughness on the embedded one.

Critical Patterns

1. Author inside <visual>, not on the link. The override auto-scopes to exactly the mesh it sits under. A link with N <visual> elements just gets N independent overrides.
2. urdfdom / RSP / MoveIt / Isaac's converter all ignore it. assemble_robot.py strips the element from the URDF it feeds the converter, then re-applies the values to the converted USD via _parse_material_override_blocks / _apply_material_overrides.
3. Only roughness and metallic are exposed. Other UsdPreviewSurface inputs (specular, opacity, IOR) are not on the contract.
4. Range 0..1. Outside that range the importer warns and clamps.
5. No attributes needed. Scoping is positional. Don't try to target a sibling visual by name — author one override per visual.

Schema

<visual>
  <origin xyz="0 0 0" rpy="0 0 0"/>
  <geometry>
    <mesh filename="package://.../base_link.dae"/>
  </geometry>
  <material_override>
    0.45
    0.85