feat(icp): extrinsic dataclass + JSON persistence

data_only_viz/lidar_calib.py

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+"""iPhone LiDAR (ARKit world) <-> webcam (Multi-HMR camera) extrinsic.
+
+Persisted as a small JSON document so calibration survives across launches.
+The default location is ``~/.config/av-live/lidar_extrinsic.json``; override
+with the ``ICP_LIDAR_EXTRINSIC`` env var.
+"""
+from __future__ import annotations
+
+import json
+import os
+from dataclasses import dataclass, field
+from pathlib import Path
+
+import numpy as np
+
+DEFAULT_EXTRINSIC_PATH = Path.home() / ".config" / "av-live" / "lidar_extrinsic.json"
+
+
+@dataclass
+class Extrinsic:
+    """4x4 rigid transform from ARKit world frame to Multi-HMR camera frame."""
+
+    T_arkit_to_cam: np.ndarray = field(default_factory=lambda: np.eye(4))
+    confidence: float = 0.0
+    captured_at_iso: str = ""
+
+    @staticmethod
+    def identity() -> "Extrinsic":
+        return Extrinsic(T_arkit_to_cam=np.eye(4), confidence=0.0, captured_at_iso="")
+
+
+def save_extrinsic(e: Extrinsic, path: Path | None = None) -> Path:
+    path = Path(path) if path is not None else _path_from_env()
+    path.parent.mkdir(parents=True, exist_ok=True)
+    payload = {
+        "T_arkit_to_cam": e.T_arkit_to_cam.astype(float).tolist(),
+        "confidence": float(e.confidence),
+        "captured_at_iso": e.captured_at_iso,
+    }
+    path.write_text(json.dumps(payload, indent=2))
+    return path
+
+
+def load_extrinsic(path: Path | None = None) -> Extrinsic:
+    path = Path(path) if path is not None else _path_from_env()
+    if not path.exists():
+        return Extrinsic.identity()
+    payload = json.loads(path.read_text())
+    return Extrinsic(
+        T_arkit_to_cam=np.array(payload["T_arkit_to_cam"], dtype=np.float64),
+        confidence=float(payload.get("confidence", 0.0)),
+        captured_at_iso=str(payload.get("captured_at_iso", "")),
+    )
+
+
+def _path_from_env() -> Path:
+    p = os.environ.get("ICP_LIDAR_EXTRINSIC")
+    return Path(p) if p else DEFAULT_EXTRINSIC_PATH

data_only_viz/tests/test_lidar_calib.py

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+"""Tests for LiDAR <-> webcam extrinsic calibration persistence."""
+from __future__ import annotations
+
+import json
+from pathlib import Path
+
+import numpy as np
+import pytest
+
+
+def test_extrinsic_default_is_identity() -> None:
+    from data_only_viz.lidar_calib import Extrinsic
+
+    e = Extrinsic.identity()
+    np.testing.assert_allclose(e.T_arkit_to_cam, np.eye(4))
+    assert e.confidence == 0.0
+    assert e.captured_at_iso == ""
+
+
+def test_extrinsic_roundtrip_json(tmp_path: Path) -> None:
+    from data_only_viz.lidar_calib import Extrinsic, load_extrinsic, save_extrinsic
+
+    T = np.eye(4)
+    T[:3, 3] = [0.1, -0.05, 0.30]
+    e = Extrinsic(T_arkit_to_cam=T, confidence=0.95, captured_at_iso="2026-05-14T12:00:00Z")
+
+    path = tmp_path / "extrinsic.json"
+    save_extrinsic(e, path)
+    loaded = load_extrinsic(path)
+
+    np.testing.assert_allclose(loaded.T_arkit_to_cam, T, atol=1e-10)
+    assert loaded.confidence == pytest.approx(0.95)
+    assert loaded.captured_at_iso == "2026-05-14T12:00:00Z"
+
+
+def test_load_extrinsic_missing_path_returns_identity(tmp_path: Path) -> None:
+    from data_only_viz.lidar_calib import load_extrinsic
+
+    e = load_extrinsic(tmp_path / "does-not-exist.json")
+    np.testing.assert_allclose(e.T_arkit_to_cam, np.eye(4))
+    assert e.confidence == 0.0