4.Parameter registry (normative)

The registry is the authoritative list of every dimension. Each row is one dimension (sided dimensions exist as an _l/_r pair sharing the listed definition). Defaults are the neutral, normalized value.

4.1.arm

Hand position in the neck-centric frame, with a separate calibrated length scale for each axis, plus elbow spread. All bipolar except a_spread (unipolar).

Legend: each drawn segment is the reference distance d of one axis — X wrist_r → middle_tip_r (hand open, bind pose) · Y neck → navel (bind pose) · Z shoulder_r → wrist_r (arm fully extended, native wrist orientation). The axis unit is L = 2 · r · d, not the drawn length itself; a normalized value n moves the hand n × max × L along that body-frame axis. The right side defines the units for both arms; distances are never remeasured from the animated pose.

Distances MUST be measured between calibrated Body sites, including their bone-local offsets, in fixed reference poses. They MUST NOT be remeasured from the animated posture: bending the elbow, curling a finger or turning the body must not change the units. The right-side reference defines the common units for both arms; left/right position signs still follow §3.2. A change to calibrated sites or effective hand geometry requires recomputing the affected reference distances.

For each axis, the physical unit is , where d is the calibrated reference distance above and r is a fixed per-axis reference ratio defined by the official reference avatar (based); it retains the established numeric scale. Thus the X unit is 2 · r · hand length (wrist → middle fingertip), the Y unit is 2 · r · torso length (neck → navel) and the Z unit is 2 · r · arm length (shoulder → wrist, extended); no unit is the bare length itself. A normalized arm coordinate n produces a displacement along its body-frame axis, before anchor/contact corrections. Equivalently, a consumer using shoulder-width units multiplies that axis by . Thus shoulder width alone no longer defines arm placement across avatars. The registry ids, maxima and defaults below remain unchanged.

A consumer lacking a valid reference measurement SHOULD use its legacy shoulder-width unit for that axis and report the missing calibration. Such a fallback does not establish calibrated-axis conformance for that avatar.

4.2.palm facing

Wrist orientation as the vector part of a body-frame global unit quaternion (w reconstructed on decode); gimbal-free. Identity (0,0,0) = palm to front, fingers up. The right hand mirrors across the sagittal plane. Defaults encode "hand hangs following the forearm, palm toward body".

Legend: identity (0,0,0) = palm toward the viewer (+z), fingers up (+y), shown on the right hand (thumb on the viewer's left). w_qx rotates about x (pitch), w_qy about y (pronate), w_qz about z (roll); axes as in Figure 2.

A consumer MUST reconstruct the scalar part from the unit-length constraint:

If the squared norm of the vector part exceeds 1, the consumer MUST rescale the vector part to length at most 1 before reconstructing, and SHOULD clamp it slightly below 1 (e.g. 0.98) to avoid the singularity near w = 0. Taking w ≥ 0 always also makes the representation unambiguous (q and −q are the same rotation).

4.3.fingers

Per finger curl / fold / side on both hands; the thumb adds a 4th DOF (roll). The thumb is bound ~90° rotated, so its fold = opposition (across the palm) and side = abduction (in/out of the palm plane). g_thumb_roll is frequently unobservable from 2D pose; a producer that cannot estimate it MUST emit the default (0). All bipolar, max 1, default 0.

Legend: columns −1 · 0 · +1. Curl (top row; joints marked): −1 = the finger curves backward along its middle and tip joints · 0 = straight · +1 = hooked toward the palm. Fold (middle row; base-knuckle pivot marked): the whole straight finger rotates about the base knuckle — −1 = raised backward · 0 = straight · +1 = folded down toward the palm (≈ 90°). Side (bottom row, index finger highlighted): −1 = toward the thumb · +1 = toward the pinky.

Legend: right hand, palm toward the viewer; columns −1 · 0 · +1. Thumb fold = opposition (top row): −1 = swung away from the palm · +1 = across the palm toward the pinky base. Thumb side = abduction (bottom row): −1 = in, pressed to the palm · +1 = out of the palm plane, toward the viewer. Thumb roll is not drawn.

4.4.head (affect-capable)

Head Euler angles (stored bipolar, degrees). Affect-capable.

4.5.body (affect-capable)

Torso motion distributed along the spine (degrees). Affect-capable.

4.6.face (affect-capable)

Bipolar expression dims; each drives one or more ARKit-named morph channels per direction. All max 1, default 0. Affect-capable.

4.7.mouth (affect-capable)

Bipolar mouth/oral shapes; each recruits several ARKit morphs per direction so the extremes reach strong shapes (yawn, kiss, bared teeth). Cheeks, tongue, and teeth are oral articulators grouped here. All max 1, default 0. Affect-capable.

When mouthing is active, the artist viseme_* morph remains the primary shape and m_* is a bounded delta from that shape. The normalized viseme mix supplies a share-weighted implied baseline b; decode sends only through the ARKit mouth channels. Therefore an authored zero leaves the artist viseme untouched, a same-direction adjustment uses only the remaining range, and an opposing adjustment can cancel it. The conservative seed table is viseme_aa → m_jaw +0.7 and viseme_PP → m_jaw −0.7, m_press +0.7; other pairs imply zero until tuned.

4.8.hyper conditions

Discrete/conditional channels carried alongside the continuous vector — see §3.4. (Section renamed from "4.cat categorical channels" in pre-release drafts; ids unchanged.)