state_tf.cpp

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#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include "math.h"
#include "corobot_msgs/PosMsg.h"
#include "nav_msgs/Odometry.h"
#include <dynamic_reconfigure/server.h>
#include <corobot_state_tf/corobot_state_tfConfig.h>

long _PreviousLeftEncoderCounts = 0;
long _PreviousRightEncoderCounts = 0;
ros::Time current_time_encoder, last_time_encoder;
double DistancePerCount; //to calculate - distance in meter for one count of the encoders.The Phidget C API gives the number of encoder ticks *4.
double lengthBetweenTwoWheels; //distance in meters between the left and right wheels, taken in the middle. 
/*Measures for Corobot:
 *Diameter of wheel = 10.5 cm
 *Distance between wheels = 21cm
 *ticks per revolution 12*52

  Measures forExplorer:
 *Diameter of wheel = 20.32 cm
 *Distance between wheels = 48.895cm
 *ticks per revolution ??
 */
double x;
double y;
double th;

double vx;
double vy;
double vth;
double dt;

int firstTime;
bool isExplorer, isCorobot4WD, publish_odom_tf;
bool odometry_activated = true;

void WheelCallback(const corobot_msgs::PosMsg::ConstPtr& pos)
{
  current_time_encoder = pos->header.stamp;
  long deltaLeft;
  long deltaRight;
  //current_time_encoder = ros::Time::now();
  dt = (current_time_encoder - last_time_encoder).toSec();
  if (dt>0.01){
          if(firstTime != 0)
          {
                deltaLeft = (pos->px - _PreviousLeftEncoderCounts);

                deltaRight = (pos->py - _PreviousRightEncoderCounts);
            
            double vl = 0.0,vr = 0.0;
            vl = ((double)deltaLeft * DistancePerCount); //distance made by the left wheel
            vr = ((double)deltaRight * DistancePerCount); //distance made by the right wheel
            
            vx = (vl+vr)/2.0;
            vth = (vr-vl)/lengthBetweenTwoWheels; //rotation made by the robot
            double delta_x = 0.0, delta_y = 0.0, delta_th = 0.0;
            delta_x = (vx * cos(th) - vy * sin(th));
            delta_y = (vx * sin(th) + vy * cos(th));
            delta_th = vth;
            x += delta_x;
            y += delta_y;
            int mod = (int) ((th+delta_th)/(2*M_PI));
            th = (th+ delta_th) -(mod*2*M_PI);
          }
          else
            firstTime = 1;
          _PreviousLeftEncoderCounts = pos->px;
          _PreviousRightEncoderCounts = pos->py;
          last_time_encoder = current_time_encoder;
    }
}

void dynamic_reconfigureCallback(corobot_state_tf::corobot_state_tfConfig &config, uint32_t level) {
                odometry_activated = config.camera_state_tf;
}

int main(int argc, char** argv){
  ros::init(argc, argv, "corobot_state_tf");
  ros::NodeHandle n;
  ros::NodeHandle nh("~");
  nh.param("Explorer", isExplorer, false);
  nh.param("Corobot4WD", isCorobot4WD, false);
  nh.param("publish_odom_tf", publish_odom_tf, true);

    dynamic_reconfigure::Server<corobot_state_tf::corobot_state_tfConfig> server;
    dynamic_reconfigure::Server<corobot_state_tf::corobot_state_tfConfig>::CallbackType f;

    f = boost::bind(&dynamic_reconfigureCallback, _1, _2);
    server.setCallback(f);
  if (isExplorer)
  {
        DistancePerCount = (M_PI*0.2032)/(500.0*59.0*4.0);
        lengthBetweenTwoWheels = 0.48895;
  }
  else if (isCorobot4WD)
  {
        DistancePerCount = (M_PI*0.109)/(12.0*52.0*4.0);
        lengthBetweenTwoWheels = 0.31 + 0.03; //length between left front and rear right wheel, plus a little more to compensate for the slipping 
  }
  else
  {
        DistancePerCount = (M_PI*0.109)/(12.0*52.0*4.0);
        lengthBetweenTwoWheels = 0.282;
  }
  _PreviousLeftEncoderCounts = 0;
  _PreviousRightEncoderCounts = 0;
  vx = 0;
  vy = 0;
  vth = 0;
  firstTime = 0;

  ros::Subscriber sub = n.subscribe("/position_data", 1000, WheelCallback);
  ros::Publisher odom_pub = n.advertise<nav_msgs::Odometry>("odometry", 50);   
  tf::TransformBroadcaster odom_broadcaster;

  ros::Rate r(50);
  ros::Rate r_deactivated(2);

  tf::TransformBroadcaster broadcaster;

  while(n.ok()){
    ros::spinOnce();
    if (odometry_activated)
    {
            if (isExplorer)
                broadcaster.sendTransform(tf::StampedTransform(tf::Transform(tf::Quaternion(0, 0, 0, 1), tf::Vector3(0.2413, 0, 0)),ros::Time::now(),"base_link", "laser"));
            else
                broadcaster.sendTransform(tf::StampedTransform(tf::Transform(tf::Quaternion(0, 0, 0, 1), tf::Vector3(0.15, 0, 0)),ros::Time::now(),"base_link", "laser"));

            //since all odometry is 6DOF we'll need a quaternion created from yaw
            geometry_msgs::Quaternion odom_quat = tf::createQuaternionMsgFromYaw(th);
            geometry_msgs::Quaternion odom_quat2 = tf::createQuaternionMsgFromYaw(0);

            //first, we'll publish the transform over tf
            geometry_msgs::TransformStamped odom_trans;
            odom_trans.header.stamp = ros::Time::now();
            odom_trans.header.frame_id = "odom";
            odom_trans.child_frame_id = "base_footprint";

            odom_trans.transform.translation.x = x;
            odom_trans.transform.translation.y = y;
            odom_trans.transform.translation.z = 0.0;
            odom_trans.transform.rotation = odom_quat;

            geometry_msgs::TransformStamped odom_trans2;
            odom_trans2.header.stamp = current_time_encoder;
            odom_trans2.header.frame_id = "base_footprint";
            odom_trans2.child_frame_id = "base_link";

            odom_trans2.transform.translation.x = 0;
            odom_trans2.transform.translation.y = 0;
            odom_trans2.transform.translation.z = 0.0;
            odom_trans2.transform.rotation = odom_quat2;


            //send the transform
            if(publish_odom_tf)
                odom_broadcaster.sendTransform(odom_trans);
            odom_broadcaster.sendTransform(odom_trans2);

            //next, we'll publish the odometry message over ROS
            nav_msgs::Odometry odom;
            odom.header.stamp = current_time_encoder;
            odom.header.frame_id = "odom";

            //set the position
            odom.pose.pose.position.x = x;
            odom.pose.pose.position.y = y;
            odom.pose.pose.position.z = 0.0;
            odom.pose.pose.orientation = odom_quat;
            odom.pose.covariance[0] = 0.01;
            odom.pose.covariance[7] = 0.01;
            odom.pose.covariance[14] = 10000;
            odom.pose.covariance[21] = 10000;
            odom.pose.covariance[28] = 10000;
            odom.pose.covariance[35] = 0.1;


            //set the velocity
            odom.child_frame_id = "base_link";
            if (dt!=0)
            {
                odom.twist.twist.linear.x = vx/dt;
                odom.twist.twist.linear.y = vy/dt;
                odom.twist.twist.angular.z = vth/dt;
            }
            else
            {
                odom.twist.twist.linear.x = 0;
                odom.twist.twist.linear.y = 0;
                odom.twist.twist.angular.z = 0;
            }
            odom.twist.covariance[0] = 0.01;
            odom.twist.covariance[7] = 0.01;
            odom.twist.covariance[14] = 10000;
            odom.twist.covariance[21] = 10000;
            odom.twist.covariance[28] = 10000;
            odom.twist.covariance[35] = 0.1;

            //publish the message
            odom_pub.publish(odom);

            r.sleep();
        }
        else
            r_deactivated.sleep();
  }
}