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在机器人的控制中，坐标系统是非常重要的，在ROS使用tf软件库进行坐标转换。
相关链接：http://www.ros.org/wiki/tf/Tutorials#Learning_tf
$ rosdep install turtle_tf rviz
$ rosmake turtle_tf rviz
可以发现，第二只乌龟会跟随你移动的乌龟进行移动。
$ rosrun tf view_frames
我们也可以通过rviz的图形界面更加形象的看到这三者之间的关系。
$ rosrun rviz rviz -d `rospack find turtle_tf`/rviz/tule_rviz.rviz
cd catkin_ws/src/
catkin_create_pkg learning_tf tf roscpp rospy turtlesim
建立你的新包roscd之前:
$ cd ~/catkin_ws
$ catkin_make
$ source ./devel/setup.bash
我们首先创建源文件。 我们刚刚创建的包:
$ roscd learning_tf
去 src / 文件夹并打开你最喜欢的编辑器,将下面的代码粘贴到一个新文件 src / 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;
};
现在我们创建代码,允许编译它。 打开 CMakeLists.txt 底部文件,并添加以下行:
add_executable(turtle_tf_broadcaster src/turtle_tf_broadcaster.cpp)
target_link_libraries(turtle_tf_broadcaster ${catkin_LIBRARIES})
Build your package; at the top folder of your catkin workspace:
$ catkin_make
创建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>
运行：
$ roslaunch learning_tf start_demo.launch
可以看到界面中只有移植乌龟了，打开tf_echo的信息窗口：
$ rosrun tf tf_echo /world /turtle1
world参考系的原点在最下角，对于turtle1的转换关系，其实就是turtle1在world参考系中所在的坐标位置以及旋转角度。
这一步，我们将看到如何使用tf进行参考系转换。首先写一个tf listener(turtle_tf_listener.cpp)
. The turtlesim/Velocity.h header is not used anymore(再也不), it has been replaced by geometry_msgs/Twist.h. Furthermore(此外), the topic /turtle/command_velocity is now called /turtle/cmd_vel. In light of this, a few changes are necessary to make it work:
#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;
};
修改 CMakeLists.txt
gedit CMakeLists.txt
add_executable(turtle_tf_listener src/turtle_tf_listener.cpp)
target_link_libraries(turtle_tf_listener ${catkin_LIBRARIES})
Build your package; at the top folder of your catkin workspace:
$ catkin_make
修改 launch文件start_demo.launch添加：
<launch>
...
<node pkg="learning_tf" type="turtle_tf_listener"
name="listener" />
</launch>
然后在运行：
$ roslaunch learning_tf start_demo.launch
就可以看到两只turtle了，也就是我们在最开始见到的那种跟随效果。
#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 CMakeLists.txt
gedit CMakeLists.txt
add_executable(frame_tf_broadcaster src/frame_tf_broadcaster.cpp)
target_link_libraries(frame_tf_broadcaster ${catkin_LIBRARIES})
Build your package; at the top folder of your catkin workspace:
$ catkin_make
修改 launch文件start_demo.launch添加：
<launch>
...
<node pkg="learning_tf" type="frame_tf_broadcaster"
name="broadcaster_frame" />
</launch>
然后在运行：
$ roslaunch learning_tf start_demo.launch
发现效果跟以前一样
Open the src/turtle_tf_listener.cpp file, and simple replace "/turtle1" with "/carrot1" in lines 26-27:
listener.lookupTransform("/turtle2", "/carrot1",
ros::Time(0), transform);
重新编译
Build your package; at the top folder of your catkin workspace:
$ catkin_make
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原文地址：http://www.cnblogs.com/CZM-/p/5879845.html
