feat(sensors): barometer thrust compensation with online estimator

Add propwash-induced barometer error compensation. Propellers create
static pressure changes at the baro sensor proportional to motor output.
Correction: baro_alt += SENS_BARO_PCOEF * mean_motor_output.

Thrust compensation in VehicleAirData uses a motor ring buffer (8
samples) with time-matched lookup against baro timestamp_sample.

BMP388 timestamp_sample corrected from read time to integration
midpoint (- measurement_time/2), eliminating 38ms baro-thrust lag.

Online estimator module (baro_thrust_estimator) uses a complementary
filter to isolate thrust-correlated baro error at 0.05Hz crossover, and
recursive least squares to identify gain K online. Saves to
SENS_BARO_PCOEF on disarm. Controlled by SENS_BAR_AUTOCAL bit 1.

SENS_BAR_AUTOCAL migrated from boolean to bitmask (bit 0: GNSS cal,
bit 1: thrust comp).

Includes offline calibration/validation tool
(Tools/baro_compensation/baro_thrust_calibration.py).

Author: dakejahl

ROMFS/px4fmu_common/init.d/rc.mc_apps

@@ -29,6 +29,13 @@ fi
 # Start Multicopter Position Controller.
 #
 mc_hover_thrust_estimator start
+
+# Bit 1 of SENS_BAR_AUTOCAL enables online thrust compensation (value > 1)
+if param greater -s SENS_BAR_AUTOCAL 1
+then
+	baro_thrust_estimator start
+fi
+
 flight_mode_manager start
 mc_pos_control start
 

Tools/baro_compensation/README.md

@@ -0,0 +1,153 @@
+# Barometer Thrust Compensation Analysis
+
+Post-flight analysis tool for barometer thrust compensation. Works with the
+online `baro_thrust_estimator` module and/or a range sensor for ground truth.
+
+## Background
+
+Propwash from propellers changes the static pressure at the barometer sensor.
+This creates a thrust-dependent altitude error: as thrust increases, the baro
+reading shifts. The direction and magnitude depend on sensor placement relative
+to the propellers.
+
+The `vehicle_air_data` module compensates for this by applying a correction to
+the barometer altitude before publishing:
+
+```
+corrected_baro_alt = raw_baro_alt + SENS_BARO_PCOEF * abs(thrust_z)
+```
+
+where `thrust_z` is the Z body-axis component (`vehicle_thrust_setpoint.xyz[2]`),
+which is signed in PX4 (negative for upward thrust in FRD). The correction uses
+its magnitude `|thrust_z|` in [0, 1]. Using the vertical thrust setpoint (rather
+than individual motor outputs) provides correct behavior for both multicopter and
+VTOL aircraft.
+
+## How Calibration Works
+
+### Online (Preferred)
+
+The online estimator is disabled by default. Enable it by setting
+`SENS_BAR_AUTOCAL` bit 1 (e.g. set to 3 for both GNSS cal and thrust comp).
+The `baro_thrust_estimator` module identifies `SENS_BARO_PCOEF` automatically
+during flight using an accel-baro complementary filter and RLS estimation.
+Parameters are saved to flash on disarm once converged, and the estimator
+continues to refine PCOEF over subsequent flights. No range sensor required.
+
+### Offline (This Tool)
+
+This tool identifies PCOEF from a flight log using a range sensor as ground
+truth. Useful for:
+- Validating online estimator results against ground truth
+- Analyzing compensation effectiveness
+- Initial calibration when the online estimator hasn't converged yet
+
+## Prerequisites
+
+- **Python packages**: `pyulog`, `numpy`, `matplotlib`
+
+  ```bash
+  pip install pyulog numpy matplotlib
+  ```
+
+## Analysis Modes
+
+The tool automatically selects a mode based on what data is in the log:
+
+### 1. Estimator Review (online estimator logged, no range sensor)
+
+Shows what the online estimator did during the flight:
+- K estimate convergence with uncertainty band
+- Prediction error and thrust excitation
+- Convergence status timeline
+- Compensation effect (residual before/after correction)
+
+### 2. Full Validation (online estimator + range sensor)
+
+Cross-validates the online estimator against range-sensor ground truth:
+- All estimator review plots (above)
+- Side-by-side comparison of online vs offline compensation
+- Scatter plots comparing raw, online-corrected, and offline-corrected error
+
+### 3. Standalone Calibration (range sensor, no estimator)
+
+Identifies PCOEF from baro vs range error:
+- Cross-correlation delay analysis
+- Recommended PCOEF value
+
+## Usage
+
+```bash
+python3 baro_thrust_calibration.py <path/to/log.ulg> [--output-dir <dir>]
+```
+
+## Output
+
+### Console
+
+Summary including parameters found in the log, online estimator convergence
+status, range-based error statistics, and cross-validation between online and
+offline identification (when both are available).
+
+### PDF Report (`<log_name>.pdf`)
+
+Pages vary by mode. When the online estimator is present:
+
+**Altitude Overview** — Baro observation, EKF altitude, distance sensor (if
+available), and thrust over time.
+
+**Estimator Convergence** — K estimate with variance band, error variance
+and thrust excitation, convergence flags over time.
+
+**Compensation Effect** — CF residual before/after applying estimated K,
+scatter plots, and compensation statistics.
+
+When a range sensor is present, additional pages show:
+
+**Compensation Comparison** — Side-by-side baro/range altitude with online
+vs offline correction applied.
+
+**Online vs Offline Scatter** — Error vs thrust scatter for raw, online-
+corrected, and offline-corrected data.
+
+## Manual Calibration Procedure
+
+If not using the online estimator, you can calibrate manually:
+
+1. **Disable existing compensation**:
+   ```
+   param set SENS_BARO_PCOEF 0.0
+   ```
+
+2. **Fly a hover** at 2-5 m AGL for at least 60 seconds with some gentle
+   altitude changes. A range sensor must be installed.
+
+3. **Run this tool** on the log and apply the recommended parameter:
+   ```
+   param set SENS_BARO_PCOEF <value>
+   ```
+
+4. **Fly again** and re-run the tool to verify (it will auto-detect validation
+   mode when compensation parameters are active).
+
+## Interpreting Results
+
+| Metric | Good | Marginal | Poor |
+|--------|------|----------|------|
+| Thrust correlation abs(r) | > 0.6 | 0.3 - 0.6 | < 0.3 |
+| Model R^2 | > 0.3 | 0.1 - 0.3 | < 0.1 |
+| Compensated abs(r) | < 0.2 | 0.2 - 0.4 | > 0.4 |
+
+- **Low R^2**: Thrust is not the dominant baro error source. Consider thermal
+  drift, ground effect, or sensor placement issues.
+- **Very large K (> 5 m)**: May indicate a sensor mounting issue. The baro
+  should be shielded from direct propwash where possible.
+- **Online/offline K disagreement > 2 m**: The estimator may not have had
+  enough excitation. Fly longer or with more altitude variation.
+
+## Parameters Reference
+
+| Parameter | Description | Range | Default |
+|-----------|-------------|-------|---------|
+| `SENS_BARO_PCOEF` | Baro altitude correction per unit vertical thrust [m] | -30 to 30 | 0.0 |
+| `SENS_BAR_AUTOCAL` | Bitmask: bit 0 = GNSS offset, bit 1 = online thrust cal | 0 to 3 | 1 |