control_toolbox::LowPassFilter< T > Class Template Reference

A Low-pass filter class. More...

#include <low_pass_filter.hpp>

Public Member Functions
	LowPassFilter (double sampling_frequency, double damping_frequency, double damping_intensity)
	~LowPassFilter ()
	Destructor of LowPassFilter class.
bool	configure ()
	Configure the LowPassFilter (access and process params).
bool	configure (const T &initial_state)
	Configure the LowPassFilter and initialize its internal state.
bool	update (const T &data_in, T &data_out)
	Applies one iteration of the IIR filter.
bool	is_configured () const
void	set_params (double sampling_frequency, double damping_frequency, double damping_intensity)
	Internal computation of the feedforward and feedbackward coefficients according to the LowPassFilter parameters.

Detailed Description

template<typename T>
class control_toolbox::LowPassFilter< T >

A Low-pass filter class.

This class implements a low-pass filter for various data types based on an Infinite Impulse Response Filter. For vector elements, the filtering is applied separately on each element of the vector.

In particular, this class implements a simplified version of an IIR filter equation :

\(y(n) = b x(n-1) + a y(n-1)\)

where:

• \( x(n)\) is the input signal
• \( y(n)\) is the output signal (filtered)
• \( b \) is the feedforward filter coefficient
• \( a \) is the feedback filter coefficient

and the Low-Pass coefficient equation:

• \( a = e^{\frac{-1}{sf} \frac{2\pi df}{10^{\frac{di}{-10}}}} \)
• \( b = 1 - a \)

where:

• \( sf \) is the sampling frequency
• \( df \) is the damping frequency
• \( di \) is the damping intensity (amplitude)

Usage

For manual instantiation, you should first call configure() (in non-realtime) and then call update() at every update step.

Member Function Documentation

configure() [1/2]

template<typename T >

bool control_toolbox::LowPassFilter< T >::configure

(

)

Configure the LowPassFilter (access and process params).

The internal state is left uninitialized, so that the filter is initialized with the input of the first update() call.

Returns

true

configure() [2/2]

template<typename T >

bool control_toolbox::LowPassFilter< T >::configure

(

const T &

initial_state

)

Configure the LowPassFilter and initialize its internal state.

In contrast to configure(), the filter starts from initial_state instead of from the input of the first update() call. The first update() therefore returns the stored signal values from initial_state, and the filter converges towards the input from there (metadata, if any, is still taken from the update() input).

Parameters

initial_state

Initial state of the filter

Returns

false if initial_state is not finite, leaving the filter unchanged, true otherwise

update()

template<typename T >

bool control_toolbox::LowPassFilter< T >::update	(	const T &	data_in,
		T &	data_out
	)

Applies one iteration of the IIR filter.

Parameters

data_in	input to the filter
data_out	filtered output

Returns

false if filter is not configured, true otherwise

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The documentation for this class was generated from the following file:

• control_toolbox/control_toolbox/include/control_toolbox/low_pass_filter.hpp