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// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/****************************************************************************
*
* Copyright (C) 2012 PX4 Development Team. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name PX4 nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/// @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:
// constructor
LowPassFilter2p(float sample_freq, float cutoff_freq) {
// set initial parameters
set_cutoff_frequency(sample_freq, cutoff_freq);
_delay_element_1 = _delay_element_2 = 0;
}
/**
* 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(void) const {
return _cutoff_freq;
}
/**
* Reset the filter state to this value
*/
float reset(float sample);
private:
float _cutoff_freq;
float _a1;
float _a2;
float _b0;
float _b1;
float _b2;
float _delay_element_1; // buffered sample -1
float _delay_element_2; // buffered sample -2
};
} // namespace math
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