float32 scan_time # time between scans [seconds]
float32 range_min # minimum range value [m]
float32 range_max # maximum range value [m]
float32[] ranges # range data [m] (Note: values < range_min or > range_max should be discarded)
float32[] intensities # intensity data [device-specific units]
备注中已经详细介绍了每个参数的意义。
2.2、通过代码发布LaserScan消息
使用ROS发布LaserScan格式的激光消息非常简洁，下边是一个简单的例程：
#include
#include
int main(int argc, char** argv){
ros::init(argc, argv, "laser_scan_publisher");
ros::NodeHandle n;
ros::Publisher scan_pub = n.advertise("scan", 50);
unsigned int num_readings = 100;
double laser_frequency = 40;
double ranges[num_readings];
double intensities[num_readings];
int count = 0;
ros::Rate r(1.0);
while(n.ok()){
//generate some fake data for our laser scan
for(unsigned int i = 0; i < num_readings; ++i){
ranges[i] = count;
intensities[i] = 100 + count;
}
ros::Time scan_time = ros::Time::now();
//populate the LaserScan message
sensor_msgs::LaserScan scan;
scan.header.stamp = scan_time;
scan.header.frame_id = "laser_frame";
scan.angle_min = -1.57;
scan.angle_max = 1.57;
scan.angle_increment = 3.14 / num_readings;
scan.time_increment = (1 / laser_frequency) / (num_readings);
scan.range_min = 0.0;
scan.range_max = 100.0;
scan.ranges.resize(num_readings);
scan.intensities.resize(num_readings);
for(unsigned int i = 0; i < num_readings; ++i){
scan.ranges[i] = ranges[i];
scan.intensities[i] = intensities[i];
}
scan_pub.publish(scan);
++count;
r.sleep();
}
}
我们将代码分解以便于分析：
#include
首先我们需要先包含Laserscan的数据结构。
ros::Publisher scan_pub = n.advertise("scan", 50);
创建一个发布者，以便于后边发布针对scan主题的Laserscan消息。
unsigned int num_readings = 100;
double laser_frequency = 40;
double ranges[num_readings];
double intensities[num_readings];
int count = 0;
ros::Rate r(1.0);
while(n.ok()){
//generate some fake data for our laser scan
for(unsigned int i = 0; i < num_readings; ++i){
ranges[i] = count;
intensities[i] = 100 + count;
}
ros::Time scan_time = ros::Time::now();
这里的例程中我们虚拟一些激光雷达的数据，如果使用真是的激光雷达，这部分数据需要从驱动中获取。
//populate the LaserScan message
sensor_msgs::LaserScan scan;
scan.header.stamp = scan_time;
scan.header.frame_id = "laser_frame";
scan.angle_min = -1.57;
scan.angle_max = 1.57;
scan.angle_increment = 3.14 / num_readings;