安装一个小实例

rosdep install turtle_tf rviz rosmake turtle_tf rviz roslaunch turtle_tf turtle_tf_demo.launch //打开一个新终端 rosrun tf view_frames /*可以看到参考系之间的联系。三个节点分别是三个参考系，而/world是其他两个乌龟参考系的父参考系。还包含一些调试需要的发送频率、最近时间等信息。*/ /*tf还提供了一个tf_echo工具来查看两个广播参考系之间的关系。我们可以看一下第二只得乌龟坐标是怎么根据第一只乌龟得出来的。*/ rosrun tf tf_echo turtle1 turtle2 //通过图形观察 rosrun rviz rviz -d `rospack find turtle_tf`/rviz/tule_rviz.rviz‘

CPP写一个broadcaster

/*turtle_tf_broadcaster.cpp*/ #include <ros/ros.h> #include <tf/transform_broadcaster.h> #include <turtlesim/Pose.h> std::string turtle_name; void poseCallback(const turtlesim::PoseConstPtr& msg){ static tf::TransformBroadcaster br; tf::Transform transform; transform.setOrigin( tf::Vector3(msg->x, msg->y, 0.0) ); tf::Quaternion q; q.setRPY(0, 0, msg->theta); transform.setRotation(q); br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "world", turtle_name)); } int main(int argc, char** argv){ ros::init(argc, argv, "my_tf_broadcaster"); if (argc != 2){ROS_ERROR("need turtle name as argument"); return -1;}; turtle_name = argv[1]; ros::NodeHandle node; ros::Subscriber sub = node.subscribe(turtle_name+"/pose", 10, &poseCallback); ros::spin(); return 0; };

还要修改CMakeList.txt

add_executable(turtle_tf_broadcaster src/turtle_tf_broadcaster.cpp) target_link_libraries(turtle_tf_broadcaster ${catkin_LIBRARIES})

编写launch文件 start_demo.launch

<launch> <!-- Turtlesim Node--> <node pkg="turtlesim" type="turtlesim_node" name="sim"/> <node pkg="turtlesim" type="turtle_teleop_key" name="teleop" output="screen"/> <!-- Axes --> <param name="scale_linear" value="2" type="double"/> <param name="scale_angular" value="2" type="double"/> <node pkg="learning_tf" type="turtle_tf_broadcaster" args="/turtle1" name="turtle1_tf_broadcaster" /> <node pkg="learning_tf" type="turtle_tf_broadcaster" args="/turtle2" name="turtle2_tf_broadcaster" /> </launch>

接下来就可以运行了。

CPP写一个TF_listener

/*turtle_tf_listener.cpp*/ #include <ros/ros.h> #include <tf/transform_listener.h> #include <geometry_msgs/Twist.h> #include <turtlesim/Spawn.h> int main(int argc, char** argv){ ros::init(argc, argv, "my_tf_listener"); ros::NodeHandle node; ros::service::waitForService("spawn"); ros::ServiceClient add_turtle = node.serviceClient<turtlesim::Spawn>("spawn"); turtlesim::Spawn srv; add_turtle.call(srv); ros::Publisher turtle_vel = node.advertise<geometry_msgs::Twist>("turtle2/cmd_vel", 10); tf::TransformListener listener; ros::Rate rate(10.0); while (node.ok()){ tf::StampedTransform transform; try{ listener.lookupTransform("/turtle2", "/turtle1", ros::Time(0), transform); } catch (tf::TransformException &ex) { ROS_ERROR("%s",ex.what()); ros::Duration(1.0).sleep(); continue; } geometry_msgs::Twist vel_msg; vel_msg.angular.z = 4.0 * atan2(transform.getOrigin().y(), transform.getOrigin().x()); vel_msg.linear.x = 0.5 * sqrt(pow(transform.getOrigin().x(), 2) + pow(transform.getOrigin().y(), 2)); turtle_vel.publish(vel_msg); rate.sleep(); } return 0; }; /* 在launch文件中添加 <node pkg="learning_tf" type="turtle_tf_listener" name="listener" /> */

添加frame

在很多应用中，添加一个参考系是很有必要的，比如在一个world参考系下，有一个激光扫描节点，tf可以帮助我们将激光扫描的信息坐标装换成全局坐标。

tf消息结构

tf中的信息是一个树状的结构，world参考系是最顶端的父参考系，其他的参考系都需要向下延伸。如果我们在上文的基础上添加一个参考系，就需要让这个新的参考系成为已有三个参考系中的一个的子参考系。

建立固定参考系

以turtle1作为父参考系，建立一个新的参考系“carrot1”

/*frame_tf_broadcaster.cpp*/ #include <ros/ros.h> #include <tf/transform_broadcaster.h> int main(int argc, char** argv){ ros::init(argc, argv, "my_tf_broadcaster"); ros::NodeHandle node; tf::TransformBroadcaster br; tf::Transform transform; ros::Rate rate(10.0); while (node.ok()){ transform.setOrigin( tf::Vector3(0.0, 2.0, 0.0) ); transform.setRotation( tf::Quaternion(0, 0, 0, 1) ); br.sendTransform(tf::StampedTransform(transform, ros::Time::now(), "turtle1", "carrot1")); rate.sleep(); } return 0; }; /*修改CMakeList.txt add_executable(frame_tf_broadcaster src/frame_tf_broadcaster.cpp) target_link_libraries(frame_tf_broadcaster ${catkin_LIBRARIES}) */ /*修改launch文件 <node pkg="learning_tf" type="frame_tf_broadcaster" name="broadcaster_frame" /> */

修改turtle_tf_listener.cpp文件

listener.lookupTransform("/turtle2", "/turtle1", ros::Time(0), transform); //改为 listener.lookupTransform("/turtle2", "/carrot1", ros::Time(0), transform);