Add saltybot_uwb_position — ROS2 Python package that reads JSON range
measurements from an ESP32 DW3000 UWB tag over USB serial, trilaterates
the robot's absolute position from 3+ fixed infrastructure anchors, and
publishes position + TF2 to the rest of the stack.
Serial protocol (one JSON line per frame):
Full frame: {"ts":…, "ranges": [{"id":0,"d_mm":1500,"rssi":-65}, …]}
Per-anchor: {"id":0, "d_mm":1500, "rssi":-65.0}
Accepts both "d_mm" and "range_mm" field names.
Trilateration (trilateration.py, numpy, no ROS deps):
Linear least-squares: linearise sphere equations around anchor 0,
solve (N-1)x2 (2D) or (N-1)x3 (3D) system via np.linalg.lstsq.
2D mode (default): robot_z fixed, needs >=3 anchors.
3D mode (solve_z=true): full 3D, needs >=4 anchors.
Outlier rejection:
After initial solve, compute per-anchor residual |r_meas - r_pred|.
Reject anchors with residual > outlier_threshold_m (0.4 m default).
Re-solve with inliers if >= min_anchors remain.
Track consecutive outlier strikes; flag in /status after N strikes.
Kalman filter (KalmanFilter3D, constant-velocity, 6-state, numpy):
Predict-only coasting when anchors drop below minimum.
Q=0.05, R=0.10 (tunable).
Topics:
/saltybot/uwb/pose PoseStamped 10 Hz Kalman-filtered position
/saltybot/uwb/range/<id> UwbRange on arrival, raw per-anchor ranges
/saltybot/uwb/status String/JSON 10 Hz state+residuals+flags
TF2: uwb_link -> map (identity rotation)
Anchor config: flat float arrays in YAML.
Default layout: 4-anchor 5x5m room at 2m height.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
