imu_filter.h

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/*
 *  Copyright (C) 2010, CCNY Robotics Lab
 *  Ivan Dryanovski <ivan.dryanovski@gmail.com>
 *
 *  http://robotics.ccny.cuny.edu
 *
 *  Based on implementation of Madgwick's IMU and AHRS algorithms.
 *  http://www.x-io.co.uk/node/8#open_source_ahrs_and_imu_algorithms
 *
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef IMU_FILTER_MADWICK_IMU_FILTER_H
#define IMU_FILTER_MADWICK_IMU_FILTER_H

#include <math.h>

#include <ros/ros.h>
#include <sensor_msgs/Imu.h>
#include <geometry_msgs/Vector3Stamped.h>
#include <tf/transform_datatypes.h>
#include <tf/transform_broadcaster.h>
#include <message_filters/subscriber.h>
#include <message_filters/synchronizer.h>
#include <message_filters/sync_policies/approximate_time.h>
#include <dynamic_reconfigure/server.h>

#include "imu_filter_madgwick/ImuFilterMadgwickConfig.h"

class ImuFilter
{
  typedef sensor_msgs::Imu              ImuMsg;
  typedef geometry_msgs::Vector3Stamped MagMsg;

  typedef message_filters::sync_policies::ApproximateTime<ImuMsg, MagMsg> SyncPolicy;
  typedef message_filters::Synchronizer<SyncPolicy> Synchronizer;
  typedef message_filters::Subscriber<ImuMsg> ImuSubscriber; 
  typedef message_filters::Subscriber<MagMsg> MagSubscriber;
  
  typedef imu_filter_madgwick::ImuFilterMadgwickConfig   FilterConfig;
  typedef dynamic_reconfigure::Server<FilterConfig>   FilterConfigServer;

  public:

    ImuFilter(ros::NodeHandle nh, ros::NodeHandle nh_private);
    virtual ~ImuFilter();

  private:

    // **** ROS-related

    ros::NodeHandle nh_;
    ros::NodeHandle nh_private_;
    
    boost::shared_ptr<Synchronizer> sync_;
    boost::shared_ptr<ImuSubscriber> imu_subscriber_;
    boost::shared_ptr<MagSubscriber> mag_subscriber_;

    ros::Publisher imu_publisher_;
    tf::TransformBroadcaster tf_broadcaster_;

    FilterConfigServer config_server_;
    
    // **** paramaters

    double gain_;     // algorithm gain
    double zeta_;         // gyro drift bias gain
    bool use_mag_;
    bool publish_tf_;
    std::string fixed_frame_;
    std::string imu_frame_;
    double constant_dt_;

    // **** state variables
  
    boost::mutex mutex_;
    bool initialized_;
    double q0, q1, q2, q3;  // quaternion
    ros::Time last_time_;
    float w_bx_, w_by_, w_bz_; // 

    // **** member functions

    void imuMagCallback(const ImuMsg::ConstPtr& imu_msg_raw,
                        const MagMsg::ConstPtr& mav_msg);

    void imuCallback(const ImuMsg::ConstPtr& imu_msg_raw);

    void publishFilteredMsg(const ImuMsg::ConstPtr& imu_msg_raw);
    void publishTransform(const ImuMsg::ConstPtr& imu_msg_raw);

    void madgwickAHRSupdate(float gx, float gy, float gz, 
                            float ax, float ay, float az, 
                            float mx, float my, float mz,
                            float dt);

    void madgwickAHRSupdateIMU(float gx, float gy, float gz, 
                               float ax, float ay, float az,
                               float dt);

    void reconfigCallback(FilterConfig& config, uint32_t level);
    
    // Fast inverse square-root
    // See: http://en.wikipedia.org/wiki/Methods_of_computing_square_roots#Reciprocal_of_the_square_root
    static float invSqrt(float x)
    {
      float xhalf = 0.5f * x;
      union
      {
        float x;
        int i;
      } u;
      u.x = x;
      u.i = 0x5f3759df - (u.i >> 1);
      /* The next line can be repeated any number of times to increase accuracy */
      u.x = u.x * (1.5f - xhalf * u.x * u.x);
      return u.x;
    }
};

#endif // IMU_FILTER_IMU_MADWICK_FILTER_H