turtle_tf2_listener_wait.py

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#!/usr/bin/env python
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import rospy

import math
import tf2_ros
import geometry_msgs.msg
import turtlesim.srv

if __name__ == '__main__':
    rospy.init_node('turtle_tf2_listener_wait')

    tfBuffer = tf2_ros.Buffer()
    listener = tf2_ros.TransformListener(tfBuffer)

    rospy.wait_for_service('spawn')
    spawner = rospy.ServiceProxy('spawn', turtlesim.srv.Spawn)
    spawner(4, 2, 0, 'turtle2')

    turtle_vel = rospy.Publisher('turtle2/cmd_vel', geometry_msgs.msg.Twist, queue_size=1)

    rate = rospy.Rate(10.0)
    while not rospy.is_shutdown():
        try:
            trans = tfBuffer.lookup_transform('turtle2', 'turtle1', rospy.Time.now(), rospy.Duration(1.0))
        except tf2_ros.Exception:
            continue

        angular = 4 * math.atan2(trans.transform.translation.y, trans.transform.translation.x)
        linear = 0.5 * math.sqrt(trans.transform.translation.x ** 2 + trans.transform.translation.y ** 2)
        msg = geometry_msgs.msg.Twist()
        msg.linear.x = linear
        msg.angular.z = angular
        turtle_vel.publish(msg)

        rate.sleep()