LowPassFilter2pVector3f.cpp

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#include "LowPassFilter2pVector3f.hpp"

#include <px4_platform_common/defines.h>

#include <math.h>

namespace math
{

void LowPassFilter2pVector3f::set_cutoff_frequency(float sample_freq, float cutoff_freq)
{
    _cutoff_freq = cutoff_freq;

    // reset delay elements on filter change
    _delay_element_1.zero();
    _delay_element_2.zero();

    if (_cutoff_freq <= 0.0f) {
        // no filtering
        _b0 = 1.0f;
        _b1 = 0.0f;
        _b2 = 0.0f;

        _a1 = 0.0f;
        _a2 = 0.0f;

        return;
    }

    const float fr = sample_freq / _cutoff_freq;
    const float ohm = tanf(M_PI_F / fr);
    const float c = 1.0f + 2.0f * cosf(M_PI_F / 4.0f) * ohm + ohm * ohm;

    _b0 = ohm * ohm / c;
    _b1 = 2.0f * _b0;
    _b2 = _b0;

    _a1 = 2.0f * (ohm * ohm - 1.0f) / c;
    _a2 = (1.0f - 2.0f * cosf(M_PI_F / 4.0f) * ohm + ohm * ohm) / c;
}

matrix::Vector3f LowPassFilter2pVector3f::reset(const matrix::Vector3f &sample)
{
    const matrix::Vector3f dval = sample / (_b0 + _b1 + _b2);

    if (PX4_ISFINITE(dval(0)) && PX4_ISFINITE(dval(1)) && PX4_ISFINITE(dval(2))) {
        _delay_element_1 = dval;
        _delay_element_2 = dval;

    } else {
        _delay_element_1 = sample;
        _delay_element_2 = sample;
    }

    return apply(sample);
}

} // namespace math