feat(viz): ARKit 91 -> MP 33 joint map

data_only_viz/arkit_joint_map.py

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+"""ARKit ARSkeleton3D 91-joint indices → MediaPipe Pose 33 indices.
+
+The ARKit ARSkeleton.JointName enum (Apple SDK) orders 91 joints
+starting with the root, hips, spine chain, shoulders, etc. We pick
+only the joints with a clear 1:1 anatomical correspondence to the
+MediaPipe Pose 33 landmark set (which is what AVLiveBody renders).
+Face/hand sub-joints (fingers, eyes) are skipped — those keep their
+existing data sources (MediaPipe Face/Hand + HaMeR MANO).
+
+Reference for ARKit joint order : Apple developer docs
+"ARSkeleton.JointName" — the canonical 91-joint list runs from
+root_joint=0 down to right_handThumbEndJoint=90.
+
+The selection here mirrors `multi.py::SMPLX_TO_MP33` so the same 14
+body slots are overridden by ARKit when fresh. Confidence comes
+from ARKit's tracking state but is not currently fanned out — we
+trust ARKit body tracking when its OSC frame is present.
+"""
+from __future__ import annotations
+
+# MediaPipe Pose 33 cardinality (cf. mediapipe pose_world_landmarks).
+MP33_NUM_LANDMARKS = 33
+
+# Pelvis = ARKit hips_joint, slot 1 in the canonical enum order.
+# Used by multi_hmr_worker for cam-translation z lock.
+ARKIT_PELVIS_IDX = 1
+
+# (arkit_joint_idx, mediapipe_pose_idx). Match the body slots used
+# by the SMPL-X body fusion in multi.py.
+ARKIT91_TO_MP33: tuple[tuple[int, int], ...] = (
+    (50, 11),   # left_shoulder_1_joint -> L_SHOULDER
+    (32, 12),   # right_shoulder_1_joint -> R_SHOULDER
+    (53, 13),   # left_arm_joint -> L_ELBOW
+    (35, 14),   # right_arm_joint -> R_ELBOW
+    (54, 15),   # left_forearm_joint -> L_WRIST
+    (36, 16),   # right_forearm_joint -> R_WRIST
+    (62, 23),   # left_upLeg_joint -> L_HIP
+    (57, 24),   # right_upLeg_joint -> R_HIP
+    (63, 25),   # left_leg_joint -> L_KNEE
+    (58, 26),   # right_leg_joint -> R_KNEE
+    (64, 27),   # left_foot_joint -> L_ANKLE
+    (59, 28),   # right_foot_joint -> R_ANKLE
+    (65, 31),   # left_toes_joint -> L_FOOT_INDEX
+    (60, 32),   # right_toes_joint -> R_FOOT_INDEX
+)

data_only_viz/tests/test_arkit_joint_map.py

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+"""ARKit 91 joints → MediaPipe Pose 33 mapping integrity."""
+from data_only_viz.arkit_joint_map import (
+    ARKIT91_TO_MP33, ARKIT_PELVIS_IDX, MP33_NUM_LANDMARKS,
+)
+
+
+def test_mapping_is_tuple_of_pairs():
+    assert isinstance(ARKIT91_TO_MP33, tuple)
+    assert len(ARKIT91_TO_MP33) > 0
+    for pair in ARKIT91_TO_MP33:
+        assert isinstance(pair, tuple)
+        assert len(pair) == 2
+
+
+def test_mapping_indices_in_range():
+    for arkit_idx, mp33_idx in ARKIT91_TO_MP33:
+        assert 0 <= arkit_idx < 91, f"arkit idx out of range: {arkit_idx}"
+        assert 0 <= mp33_idx < MP33_NUM_LANDMARKS, \
+            f"mp33 idx out of range: {mp33_idx}"
+
+
+def test_pelvis_index_valid():
+    assert 0 <= ARKIT_PELVIS_IDX < 91
+
+
+def test_no_duplicate_mp33_targets():
+    """Each MediaPipe slot must be written by at most one ARKit joint."""
+    mp33_seen = set()
+    for _, mp33_idx in ARKIT91_TO_MP33:
+        assert mp33_idx not in mp33_seen, \
+            f"mp33 slot {mp33_idx} mapped twice"
+        mp33_seen.add(mp33_idx)