ROS 接收键盘控制的虚假里程计节点编写

writer：lIcht                      email：lIcht.gzl@gmail.com                 date:  2019.11.24

       最近在ros小车底层通讯搭建的时候遇到了问题：小车无法获取实际的里程计，但是需要迫切的搭建tf树来构建上层通讯架构。所以需要一个假的里程计信息来使上层工具包能正常跑起来。

        解决思路：由于小车的地盘最终是要根据move_base发出的cmd_vel命令消息对速度进行控制，所以想到由此cmd_vel速度消息直接得到里程计信息(不根据实际的轮速反馈)，实现发布/odom主题的发布以及/odom坐标到/base_footprint坐标的tf转换。

fake_odom.cpp:

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#include <ros/ros.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>
#include <geometry_msgs/Twist.h>
  float vx;
  float vy;
  float vth;
​
​
void callback(const geometry_msgs::Twist& vel)
{
  float linear_scale = 1.06;
  vx = (vel.linear.x/1200) * linear_scale;
  vy = (vel.linear.y/1200) * linear_scale;
  vth = (vel.angular.z/1200);
}
​
​
int main(int argc, char** argv){
  ros::init(argc, argv, "odometry_publisher");
​
  float x = 0.0;
  float y = 0.0;
  float th = 0.0;
​
  ros::NodeHandle n;
  ros::Publisher odom_pub = n.advertise<nav_msgs::Odometry>("odom", 50);
  //订阅cmd_vel速度指令主题，并进入回调函数处理
  ros::Subscriber velocity = n.subscribe("cmd_vel", 50, callback);
  tf::TransformBroadcaster odom_broadcaster;
​
​
  ros::Time current_time, last_time;
  current_time = ros::Time::now();
  last_time = ros::Time::now();
​
  ros::Rate r(10);
  while(n.ok()){
​
    ros::spinOnce();     // check for incoming messages
    current_time = ros::Time::now();
​
    //compute odometry in a typical way given the velocities of the robot
    double dt = (current_time - last_time).toSec();
    double delta_x = (vx * cos(th) - vy * sin(th)) * dt;
    double delta_y = (vx * sin(th) + vy * cos(th)) * dt;
    double delta_th = vth * dt;
​
    x += delta_x;
    y += delta_y;
    th += delta_th;
​
    //since all odometry is 6DOF we'll need a quaternion created from yaw
    geometry_msgs::Quaternion odom_quat = tf::createQuaternionMsgFromYaw(th);
​
    //first, we'll publish the transform over tf
    geometry_msgs::TransformStamped odom_trans;
    odom_trans.header.stamp = current_time;
    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;
​
    //send the transform
    odom_broadcaster.sendTransform(odom_trans);
​
    //next, we'll publish the odometry message over ROS
    nav_msgs::Odometry odom;
    odom.header.stamp = current_time;
    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;
​
    //set the velocity
    odom.child_frame_id = "base_footprint";
    odom.twist.twist.linear.x = vx;
    odom.twist.twist.linear.y = vy;
    odom.twist.twist.angular.z = vth;
​
    //publish the message
    odom_pub.publish(odom);
​
    last_time = current_time;
    r.sleep();
  }
}
​

cmd_vel消息数据格式:

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rostopic pub /mobile_base_controller/cmd_vel geometry_msgs/Twist:
//可看作结构体 linear和angular为<vector>类型，x,y,z为float类型
linear:
  x: 0.5
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0

假里程计信息配合雷达信息跑gmapping SLAM的效果(能正常建图与维护动态tf):