LowPassFilter2p.hpp

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/// @file   LowPassFilter.h
/// @brief  A class to implement a second order low pass filter
/// Author: Leonard Hall <LeonardTHall@gmail.com>
/// Adapted for PX4 by Andrew Tridgell

#pragma once

namespace math
{
class __EXPORT LowPassFilter2p
{
public:

    LowPassFilter2p(float sample_freq, float cutoff_freq)
    {
        // set initial parameters
        set_cutoff_frequency(sample_freq, cutoff_freq);
    }

    // Change filter parameters
    void set_cutoff_frequency(float sample_freq, float cutoff_freq);

    /**
     * Add a new raw value to the filter
     *
     * @return retrieve the filtered result
     */
    float apply(float sample);

    // Return the cutoff frequency
    float get_cutoff_freq() const { return _cutoff_freq; }

    // Reset the filter state to this value
    float reset(float sample);

private:

    float _cutoff_freq{0.0f};

    float _a1{0.0f};
    float _a2{0.0f};

    float _b0{0.0f};
    float _b1{0.0f};
    float _b2{0.0f};

    float _delay_element_1{0.0f};   // buffered sample -1
    float _delay_element_2{0.0f};   // buffered sample -2
};

} // namespace math