Put your gesture on BDX-R

A label is not a coordinate convention

Our semantic head_yaw_deg describes an artistic direction. A model joint called Head_Yaw has its own axis. In the pinned XML, Head_Yaw points along negative Z and Head_Roll along negative X; the example mapping therefore includes explicit sign changes. A name match alone cannot determine the correct direction.

The mapping formula adds a calibrated neutral offset after converting degrees to radians and applying the sign. The example uses zero offsets for the XML study. A physical encoder zero is a different calibration and cannot be copied from this JSON.

Complete the mapping with the permitted joint-angle range as well. The name selects the joint, the sign and units define the direction and size of the request, the neutral defines its zero, and the limits bound the permitted request. Verify all five before previewing a new model.

Retargeting has several levels

At the simplest level, retargeting converts an intended movement into another model’s coordinates. At a deeper level, different proportions, joint ranges, mass and contacts change what is achievable. Disney’s ReActor paper studies motion adaptation together with a physical tracking policy; it motivates treating those problems together.

Here we deliberately start with four hinge channels. The supplied program rejects missing joints, non-hinge joints, duplicate mappings, invalid values and samples outside the preview envelope or XML limits. Those checks are necessary but do not establish collision clearance or correct physical calibration.

Forward kinematics is a pose calculation

The preview writes qpos and calls mj_forward. It never calls mj_step, never runs a walking policy and never opens CAN. It lets you inspect how the model is arranged at each sample. The remaining joints stay at the XML default pose. A floating robot or a poor default foot stance is therefore not a successful balancing result.

Visual inspection can reveal obvious shell intersections and cable-routing concerns, but absent geometry cannot collide in a model. The physical robot has wire loops, fasteners and tolerances that may not be represented. Record those missing details for the build inspection.

Build a reusable mapping artifact

Keep the clip, JSON map, model commit and Python package versions together. Give each test a name. Change one sign or offset only after observing the single-channel result. Do not solve an uncertain orientation by flipping several axes until the full gesture looks roughly plausible.

A later dynamic experiment must retain the same observation order, control timing and policy contract used by the baseline. This small map is an authoring adapter, not a replacement for the deployment configuration.