Webots Humans and Assets

Purpose

Use this skill to build human-centric and environment-rich Webots scenes quickly and correctly:

• Add animated human meshes through CharacterSkin and BVH retargeting.
• Add walking rigid humans through Pedestrian and trajectory arguments.
• Load biomechanics motion capture through C3dViewer.
• Populate worlds with the complete projects/objects PROTO library.
• Start from pre-built environment worlds when faster than assembling from scratch.

Use references/humans_assets_reference.md as the authoritative field/API catalog.

Trigger Conditions

Activate when requests include terms such as:

• webots human, animated human, CharacterSkin
• pedestrian, walking person, crowd
• BVH animation, motion retargeting
• C3D, motion capture, markers, ground reaction force
• environment assets, furniture, indoor, outdoor, buildings, street furniture, traffic, static vehicles

Boundaries

Keep this skill focused on humans and environment assets:

• Do not explain Skin node internals beyond practical mapping requirements.
• Do not cover robot catalogs or robot model selection.
• Defer low-level physics node internals to webots-physics.

Human Model Selection Workflow

1. Choose the human representation:
   • Use CharacterSkin for mesh-based, bone-driven animation from BVH.
   • Use Pedestrian for lightweight scripted walking with path/speed args.
   • Use C3dViewer for marker-based biomechanics playback and analysis.
2. Add the node, set placement (translation, rotation), then configure behavior fields.
3. Validate scale/orientation immediately in simulation before scene duplication.

CharacterSkin (Animated Human Mesh)

Use CharacterSkin when BVH animation or pose retargeting is required.

CharacterSkin {
  translation 0 0 0
  rotation 0 0 1 0
  scale 1 1 1
  name "skin"
  model "Sandra"    # Options: "Anthony", "Robert", "Sandra", "Sophia"
  castShadows FALSE
}

Apply these model choices:

• Anthony: boy
• Robert: man
• Sandra: woman
• Sophia: girl

Practical notes:

• Treat CharacterSkin as a Skin-derived PROTO with predefined FBX mesh and PBR textures.
• Keep character scale close to 1 1 1; adjust BVH translation scale instead of nonuniform body scaling when possible.
• Keep one animation controller instance per animated character to simplify joint mapping.

BVH Playback and Retargeting Flow

Follow this sequence for robust playback:

1. Load BVH data (wbu_bvh_read_file).
2. Set translation scaling (wbu_bvh_set_scale) for meter alignment.
3. Build per-joint mapping between BVH joint indices and Webots bone identifiers.
4. Set T-pose alignment for each mapped joint (wbu_bvh_set_model_t_pose) using axis-angle data.
5. Step BVH every control loop (wbu_bvh_step), read joint rotations and root translation, then apply to the skin/bones.
6. Cleanup on exit (wbu_bvh_cleanup).

// Load BVH file
WbBvhDataRef motion = wbu_bvh_read_file("animation.bvh");
wbu_bvh_set_scale(motion, 0.01);  // scale translation data

// Set T-pose mapping for each joint
wbu_bvh_set_model_t_pose(motion, axisAngle, jointId, global);

// Play animation
while (wb_robot_step(timestep) != -1) {
    wbu_bvh_step(motion);
    for (int i = 0; i < wbu_bvh_get_joint_count(motion); i++) {
        double *rotation = wbu_bvh_get_joint_rotation(motion, i);
        // Apply rotation to Skin bone
    }
}
wbu_bvh_cleanup(motion);

Pedestrian (Rigid Walking Human)

Use Pedestrian for scripted walk cycles with simple scene integration.

Pedestrian {
  translation 0 0 1.27
  rotation 0 0 1 0
  name "pedestrian"
  controller "pedestrian"
  controllerArgs ["--speed=1.5", "--trajectory=[2 0, 0 2, -2 0]"]
  shirtColor 0.25 0.55 0.20
  pantsColor 0.24 0.25 0.5
  shoesColor 0.28 0.15 0.06
  skinColor 1.0 0.75 0.7
  enableBoundingObject FALSE
}

Use this model behavior correctly:

• 13 passive joints exist (3 per arm, 3 per leg, 1 head).
• Walking gait logic is provided by the Python pedestrian controller.
• controllerArgs typically include:
  • --trajectory=[x1 y1, x2 y2, ...]
  • --speed=<m/s>
  • --step=<controller step ms>
• Attach props through leftHandSlot and rightHandSlot.

C3D Motion Capture Viewer

Use C3dViewer to visualize biomechanics C3D files:

• Marker trajectories are rendered as spheres.
• Ground reaction force offsets are configurable.
• Playback speed and body visualization settings are configurable.
• The robot window (c3d_viewer_window) exposes runtime controls.

Environment Asset Placement Workflow

Use built-in PROTO insertion for all object assets:

Add button > PROTO nodes (Webots Projects) > objects > [category] > [asset]

Use this category-first strategy:

1. Place structural envelopes first (floors, walls, roads, buildings).
2. Place major furniture/infrastructure assets.
3. Add detail assets (street furniture, tools, props, vegetation).
4. Add background/static vehicles last to tune density and readability.

Asset Families to Prioritize

Use the object library in these practical groups:

• Furniture and interiors: tables, chairs, desks, sofas, beds, cabinets, kitchen and bathroom fixtures.
• Infrastructure: buildings, doors/windows, stairs, roads, intersections, street equipment.
• Industrial/factory: conveyors, pallets, crates, valves, tools, canisters.
• Nature: trees, plants, rocks, and static animals.
• Street furniture: benches, bus stops, bins, hydrants, kiosks, fences.
• Static/background vehicles and road context assets.

Pre-built Environments and Templates

Start from pre-built worlds when layout speed matters:

• Basic arenas: RectangleArena, CircleArena PROTO floors.
• Indoor environments: apartment/kitchen/break-room style worlds.
• Outdoor environments: city, village, road/highway worlds.
• Sports: RoboCup-style soccer field and match worlds.
• Factory floors and industrial halls.

Use the detailed world inventory in references/humans_assets_reference.md.

Validation Checklist

Before finalizing scene composition:

1. Confirm all humans stand on contact surfaces without penetration.
2. Confirm animation scale and heading match ENU world axes.
3. Confirm pedestrian trajectory points remain navigable around obstacles.
4. Confirm static asset density preserves robot navigation corridors.
5. Confirm TexturedBackground and TexturedBackgroundLight textures match.
6. Confirm simulation remains real-time capable after asset expansion.

Reference File

Load references/humans_assets_reference.md for:

• complete CharacterSkin, Pedestrian, and C3dViewer field references,
• full BVH utility C API,
• complete categorized object PROTO catalog,
• pre-built world environment index,
• textured background/light option matrix.