上一节介绍和测试了cartographer的官方demo。

本节会编写ros系统中，最常用的激光雷达LaserScan传感数据的订阅和发布，方便在cartographer中加入自己的数据进行建图与定位。(作者使用的是SICK-NAV350)

官方文档：

http://wiki.ros.org/navigation/Tutorials/RobotSetup/Sensors

目录

1：sensor_msgs/LaserScan消息类型

2：发布LaserScan消息 

3：订阅LaserScan消息

1：sensor_msgs/LaserScan消息类型

在终端查看消息数据结构：

rosmsg show sensor_msgs/LaserScan

LaserScan消息类型数据结构如下：

std_msgs/Header header          uint32 seqtime stamp           string frame_id 　　  # in frame frame_id, angles are measured around  the positive Z axis (counterclockwise, if Z is up)# with zero angle being forward along the x axis           float32 angle_min        # start angle of the scan [rad]
 float32 angle_max        # end angle of the scan [rad]
 float32 angle_increment  # angular distance between measurements [rad]float32 time_increment   # time between measurements [seconds] - if your scanner# is moving, this will be used in interpolating position# of 3d points
 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].  If your device does not provide intensities, please leave the array empty.

得到了消息数据结构之后，就可以根据雷达数据填充消息内容。
其中angle_min angle_max angle_increment time_increment range_min range_max等基本上是雷达设置常量。
而ranges表示对应角度的测量距离，intensities表示对应角度的反射强度，这些是动态变化的，需要根据雷达频率更新。

2：发布LaserScan消息 

#include 
 #include int main(int argc, char** argv)
 {//ros节点初始化ros::init(argc, argv, "laser_scan_publisher");ros::NodeHandle n;//创建LaserScan消息发布Publisherros::Publisher scan_pub = n.advertise("scan", 50);//激光雷达参数设置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()){//为激光扫描生成一些假数据(可替换成自己激光雷达真实数据)for(unsigned int i = 0; i < num_readings; ++i){ranges[i] = count;intensities[i] = 100 + count;}ros::Time scan_time = ros::Time::now();//填充 LaserScan 消息sensor_msgs::LaserScan scan;scan.header.stamp = scan_time;scan.header.frame_id = "base_link";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];}//通过 ROS 发布消息scan_pub.publish(scan);++count;r.sleep();}
 }

3：订阅LaserScan消息

通常来说，发布自己激光雷达的信息到ros系统中，同时cartographer节点能够自动订阅接收LaserScan消息，就可以实现将雷达数据传给cartographer算法的目的。
但特定情况下可能需要订阅查看激光雷达的信息。

(1) 通过rosbag订阅

rostopic echo /scan

(2) 通过rviz查看
打开rviz

rosrun rviz rviz

Fixed Frame修改为base_link，添加LaserScan并将Topic设为/scan

 
(3) 编写程序打印

#include "ros/ros.h"
 #include "sensor_msgs/LaserScan.h"void ScanCallback(const sensor_msgs::LaserScan::ConstPtr &msg)
 {size_t size = msg->ranges.size();std::string ranges ="";for(size_t i =0; i< size;i++){ranges += std::to_string(msg->ranges[i]) + ", ";}ROS_INFO("Scan: [%s]", ranges);
 }int main(int argc, char **argv)
 {ros::init(argc, argv, "listener");ros::NodeHandle node;ros::Subscriber subScan = node.subscribe("scan", 1000, ScanCallback);ros::spin();return 0;
 }

【完】

下一节会介绍里程计Odom数据的发布和订阅。