1.The LaserScan Message
、ROS 中提供了一种很特殊的 Message type 在sensor-MSG 包当中，他是LaserScan ，他使得编码已获得的信息变得极为方便，首先看一下信息的类型。
A：激光扫描的角度是被逆时针测量的
1 Header header 2 float32 angle_min # start angle of the scan [rad] 3 float32 angle_max # end angle of the scan [rad] 4 float32 angle_increment # angular distance between measurements [rad] 5 float32 time_increment # time between measurements [seconds] 6 float32 scan_time # time between scans [seconds] 7 float32 range_min # minimum range value [m] 8 float32 range_max # maximum range value [m] 9 float32[] ranges # range data [m] (Note: values < range_min or > range_max should be discarded) 10 float32[] intensities # intensity data [device-specific units]
2. Writing Code to Publish a LaserScan Message
1 #include <ros/ros.h> 2 #include <sensor_msgs/LaserScan.h> 3 4 int main(int argc, char** argv){ 5 ros::init(argc, argv, "laser_scan_publisher"); 6 7 ros::NodeHandle n; 8 ros::Publisher scan_pub = n.advertise<sensor_msgs::LaserScan>("scan", 50); #这是要传递的信息。 9 10 unsigned int num_readings = 100; 11 double laser_frequency = 40; 12 double ranges[num_readings]; 13 double intensities[num_readings]; # 准备创建虚拟的激光信息，这分别是平率，不太懂。。。 14 15 int count = 0; 16 ros::Rate r(1.0); #发送数据的速率 17 while(n.ok()){ 18 //generate some fake data for our laser scan 19 for(unsigned int i = 0; i < num_readings; ++i){ 20 ranges[i] = count; 21 intensities[i] = 100 + count; 22 } 23 ros::Time scan_time = ros::Time::now(); #每隔一秒产生一个虚假的数据 24 25 //populate the LaserScan message 26 sensor_msgs::LaserScan scan; 27 scan.header.stamp = scan_time; 28 scan.header.frame_id = "laser_frame"; 29 scan.angle_min = -1.57; 30 scan.angle_max = 1.57; 31 scan.angle_increment = 3.14 / num_readings; 32 scan.time_increment = (1 / laser_frequency) / (num_readings); 33 scan.range_min = 0.0; 34 scan.range_max = 100.0; #这些是消息内容。与前一节交相辉映 35 36 scan.ranges.resize(num_readings); 37 scan.intensities.resize(num_readings); 38 for(unsigned int i = 0; i < num_readings; ++i){ 39 scan.ranges[i] = ranges[i]; 40 scan.intensities[i] = intensities[i]; 41 } 42 43 scan_pub.publish(scan); 44 ++count; 45 r.sleep(); 46 } 47 }
3. Publishing PointCloud Message
1 #include <ros/ros.h> 2 #include <sensor_msgs/PointCloud.h> 3 4 int main(int argc, char** argv){ 5 ros::init(argc, argv, "point_cloud_publisher"); 6 7 ros::NodeHandle n; 8 ros::Publisher cloud_pub = n.advertise<sensor_msgs::PointCloud>("cloud", 50); 9 10 unsigned int num_points = 100; 11 12 int count = 0; 13 ros::Rate r(1.0); 14 while(n.ok()){ 15 sensor_msgs::PointCloud cloud; 16 cloud.header.stamp = ros::Time::now(); 17 cloud.header.frame_id = "sensor_frame"; 18 19 cloud.points.resize(num_points); 20 21 //we\'ll also add an intensity channel to the cloud 22 cloud.channels.resize(1); 23 cloud.channels[0].name = "intensities"; 24 cloud.channels[0].values.resize(num_points); 25 26 //generate some fake data for our point cloud 27 for(unsigned int i = 0; i < num_points; ++i){ 28 cloud.points[i].x = 1 + count; 29 cloud.points[i].y = 2 + count; 30 cloud.points[i].z = 3 + count; 31 cloud.channels[0].values[i] = 100 + count; 32 } 33 34 cloud_pub.publish(cloud); 35 ++count; 36 r.sleep(); 37 } 38 }