text: ///////////////////////////////////////////////////////////////////////////////
  //      Title     : low_pass_filter.h
  //      Project   : jog_arm
  //      Created   : 1/11/2019
  //      Author    : Andy Zelenak
  //
  // BSD 3-Clause License
  //
  // Copyright (c) 2019, Los Alamos National Security, LLC
  // All rights reserved.
  //
  // Redistribution and use in source and binary forms, with or without
  // modification, are permitted provided that the following conditions are met:
  //
  // * Redistributions of source code must retain the above copyright notice, this
  //   list of conditions and the following disclaimer.
  //
  // * 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.
  //
  // * Neither the name of the copyright holder 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
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  // ARE
  // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
  // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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  ///////////////////////////////////////////////////////////////////////////////
  
  #pragma once
  
  namespace jog_arm
  {
  /**
   * Class LowPassFilter - Filter a signal to soften jerks.
   * This is a first-order Butterworth low-pass filter.
   *
   * TODO: Use ROS filters package (http://wiki.ros.org/filters, https://github.com/ros/filters)
   */
  class LowPassFilter
  {
  public:
    explicit LowPassFilter(double low_pass_filter_coeff);
    double filter(double new_measurement);
    void reset(double data);
  
  private:
    double previous_measurements_[2] = { 0., 0. };
    double previous_filtered_measurement_ = 0.;
    // Larger filter_coeff-> more smoothing of jog commands, but more lag.
    // Rough plot, with cutoff frequency on the y-axis:
    // https://www.wolframalpha.com/input/?i=plot+arccot(c)
    double filter_coeff_ = 10.;
  };
  }  // namespace jog_arm
  