integrator.cpp

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/**
 * @file integrator.cpp
 *
 * A resettable integrator
 *
 * @author Lorenz Meier <lorenz@px4.io>
 * @author Julian Oes <julian@oes.ch>
 */

#include "integrator.h"

#include <drivers/drv_hrt.h>

Integrator::Integrator(uint32_t auto_reset_interval, bool coning_compensation) :
    _coning_comp_on(coning_compensation)
{
    set_autoreset_interval(auto_reset_interval);
}

bool
Integrator::put(const hrt_abstime &timestamp, const matrix::Vector3f &val, matrix::Vector3f &integral,
        uint32_t &integral_dt)
{
    if (_last_integration_time == 0) {
        /* this is the first item in the integrator */
        _last_integration_time = timestamp;
        _last_reset_time = timestamp;
        _last_val = val;

        return false;
    }

    float dt = 0.0f;

    // Integrate:
    // Leave dt at 0 if the integration time does not make sense.
    // Without this check the integral is likely to explode.
    if (timestamp >= _last_integration_time) {
        dt = static_cast<float>(timestamp - _last_integration_time) * 1e-6f;
    }

    // Use trapezoidal integration to calculate the delta integral
    const matrix::Vector3f delta_alpha = (val + _last_val) * dt * 0.5f;
    _last_val = val;

    // Calculate coning corrections if required
    if (_coning_comp_on) {
        // Coning compensation derived by Paul Riseborough and Jonathan Challinger,
        // following:
        // Tian et al (2010) Three-loop Integration of GPS and Strapdown INS with Coning and Sculling Compensation
        // Sourced: http://www.sage.unsw.edu.au/snap/publications/tian_etal2010b.pdf
        // Simulated: https://github.com/priseborough/InertialNav/blob/master/models/imu_error_modelling.m
        _beta += ((_last_alpha + _last_delta_alpha * (1.0f / 6.0f)) % delta_alpha) * 0.5f;
        _last_delta_alpha = delta_alpha;
        _last_alpha = _alpha;
    }

    // accumulate delta integrals
    _alpha += delta_alpha;

    _last_integration_time = timestamp;

    // Only do auto reset if auto reset interval is not 0.
    if (_auto_reset_interval > 0 && (timestamp - _last_reset_time) >= _auto_reset_interval) {

        // apply coning corrections if required
        if (_coning_comp_on) {
            integral = _alpha + _beta;

        } else {
            integral = _alpha;
        }

        // reset the integrals and coning corrections
        _reset(integral_dt);

        return true;

    } else {
        return false;
    }
}

bool
Integrator::put_with_interval(unsigned interval_us, matrix::Vector3f &val, matrix::Vector3f &integral,
                  uint32_t &integral_dt)
{
    if (_last_integration_time == 0) {
        /* this is the first item in the integrator */
        hrt_abstime now = hrt_absolute_time();
        _last_integration_time = now;
        _last_reset_time = now;
        _last_val = val;

        return false;
    }

    // Create the timestamp artifically.
    const hrt_abstime timestamp = _last_integration_time + interval_us;

    return put(timestamp, val, integral, integral_dt);
}

matrix::Vector3f
Integrator::get(bool reset, uint32_t &integral_dt)
{
    matrix::Vector3f val = _alpha;

    if (reset) {
        _reset(integral_dt);
    }

    return val;
}

matrix::Vector3f
Integrator::get_and_filtered(bool reset, uint32_t &integral_dt, matrix::Vector3f &filtered_val)
{
    // Do the usual get with reset first but don't return yet.
    const matrix::Vector3f ret_integral = get(reset, integral_dt);

    // Because we need both the integral and the integral_dt.
    filtered_val = ret_integral * 1000000 / integral_dt;

    return ret_integral;
}

void
Integrator::_reset(uint32_t &integral_dt)
{
    _alpha.zero();
    _last_alpha.zero();
    _beta.zero();

    integral_dt = (_last_integration_time - _last_reset_time);

    _last_reset_time = _last_integration_time;
}