Barometer

[joeblew999]

Would like to add Barometer but am new to this repo

[wboayue]

The upstream C library doesn't include barometer support - it focuses on AHRS (gyroscope, accelerometer, magnetometer fusion) for orientation estimation.

My current priority is maintaining parity with the C implementation to ensure the core AHRS algorithm is correct and well-tested.

That said, barometric altitude would be a useful addition. The approach I'd take is implementing it as a separate filter module (e.g., AltitudeEstimator) that can be composed with AHRS output rather than integrated into the core algorithm.

A simple complementary filter or Kalman filter could work well for this:

• High-pass filtered vertical acceleration (from AHRS + accelerometer)
• Low-pass filtered barometric altitude
• Fused to get drift-corrected altitude estimate

This is the approach I plan to take eventually, but it's not on the immediate roadmap. Happy to discuss further if you're interested in contributing.

[joeblew999]

Thanks for the detailed guidance! I'd like to take a shot at implementing the AltitudeEstimator as you described.

Proposed Design

A separate module that composes with AHRS output:

pub struct AltitudeEstimator {
    // Filter coefficients
    accel_alpha: f32,  // High-pass for acceleration
    baro_alpha: f32,   // Low-pass for barometer
    
    // State
    velocity: f32,
    altitude: f32,
    baro_reference: f32,
    
    // Previous values for filtering
    prev_accel: f32,
    prev_baro_altitude: f32,
}

impl AltitudeEstimator {
    pub fn new(settings: AltitudeSettings) -> Self;
    
    /// Update with vertical acceleration (from AHRS + accelerometer) and barometric altitude
    pub fn update(
        &mut self,
        vertical_accel: f32,  // m/s², gravity-compensated using AHRS orientation
        baro_altitude: f32,   // meters, from barometer
        dt: f32,              // delta time in seconds
    ) -> AltitudeEstimate;
}

pub struct AltitudeEstimate {
    pub altitude: f32,   // meters
    pub velocity: f32,   // m/s vertical
}

Integration with AHRS

The library already provides earth_acceleration() which gives gravity-compensated acceleration in the Earth frame. The Z component is exactly what's needed:

// In update loop:
ahrs.update(gyro, accel, mag, dt);

let earth_accel = ahrs.earth_acceleration();
let vertical_accel = earth_accel.z;  // Use this for altitude estimator

let estimate = altitude_est.update(vertical_accel, baro_altitude, dt);

Implementation Plan

1. Start with a simple complementary filter (keeps it #![no_std] friendly)
2. High-pass accelerometer integration for short-term accuracy
3. Low-pass barometer for long-term drift correction
4. Configurable filter coefficients via AltitudeSettings

Questions

1. Should this live in a separate file (e.g., altitude.rs) or a subdirectory?
2. Any preference on the API naming conventions?
3. Should I include unit tests similar to the existing AHRS tests?

Happy to discuss further before I start coding!