Hi.
i am trying to get my head around why is there a
def init…
rospy.init_node(‘robot_control_node’, anonymous=True)
is it common practice to add this inside a class, as if i use the init node inside my new program when i try and call the class, it conflicts as i think you can only have one node definition?
This is the class code
#!/usr/bin/env python
import rospy
from geometry_msgs.msg import Twist
from sensor_msgs.msg import LaserScan
from nav_msgs.msg import Odometry
from tf.transformations import euler_from_quaternion, quaternion_from_euler
import time
import math
class RobotControl():
def __init__(self):
rospy.init_node('robot_control_node', anonymous=True)
self.vel_publisher = rospy.Publisher('/cmd_vel', Twist, queue_size=1)
self.summit_vel_publisher = rospy.Publisher('/summit_xl_control/cmd_vel', Twist, queue_size=1)
self.laser_subscriber = rospy.Subscriber(
'/kobuki/laser/scan', LaserScan, self.laser_callback)
self.summit_laser_subscriber = rospy.Subscriber(
'/hokuyo_base/scan', LaserScan, self.summit_laser_callback)
self.odom_sub = rospy.Subscriber ('/odom', Odometry, self.odom_callback)
self.cmd = Twist()
self.laser_msg = LaserScan()
self.summit_laser_msg = LaserScan()
self.roll = 0.0
self.pitch = 0.0
self.yaw = 0.0
self.ctrl_c = False
self.rate = rospy.Rate(10)
rospy.on_shutdown(self.shutdownhook)
def publish_once_in_cmd_vel(self):
"""
This is because publishing in topics sometimes fails the first time you publish.
In continuos publishing systems there is no big deal but in systems that publish only
once it IS very important.
"""
while not self.ctrl_c:
connections = self.vel_publisher.get_num_connections()
summit_connections = self.summit_vel_publisher.get_num_connections()
if connections > 0 or summit_connections > 0:
self.vel_publisher.publish(self.cmd)
self.summit_vel_publisher.publish(self.cmd)
#rospy.loginfo("Cmd Published")
break
else:
self.rate.sleep()
def shutdownhook(self):
# works better than the rospy.is_shutdown()
self.ctrl_c = True
def laser_callback(self, msg):
self.laser_msg = msg
def summit_laser_callback(self, msg):
self.summit_laser_msg = msg
def odom_callback(self, msg):
orientation_q = msg.pose.pose.orientation
orientation_list = [orientation_q.x, orientation_q.y, orientation_q.z, orientation_q.w]
(self.roll, self.pitch, self.yaw) = euler_from_quaternion (orientation_list)
def get_laser(self, pos):
time.sleep(1)
return self.laser_msg.ranges[pos]
def get_laser_summit(self, pos):
time.sleep(1)
return self.summit_laser_msg.ranges[pos]
def get_front_laser(self):
time.sleep(1)
return self.laser_msg.ranges[360]
def get_laser_full(self):
time.sleep(1)
return self.laser_msg.ranges
def stop_robot(self):
#rospy.loginfo("shutdown time! Stop the robot")
self.cmd.linear.x = 0.0
self.cmd.angular.z = 0.0
self.publish_once_in_cmd_vel()
def move_straight(self):
# Initilize velocities
self.cmd.linear.x = 0.5
self.cmd.linear.y = 0
self.cmd.linear.z = 0
self.cmd.angular.x = 0
self.cmd.angular.y = 0
self.cmd.angular.z = 0
# Publish the velocity
self.publish_once_in_cmd_vel()
def move_straight_time(self, motion, speed, time):
# Initilize velocities
self.cmd.linear.y = 0
self.cmd.linear.z = 0
self.cmd.angular.x = 0
self.cmd.angular.y = 0
self.cmd.angular.z = 0
if motion == "forward":
self.cmd.linear.x = speed
elif motion == "backward":
self.cmd.linear.x = - speed
i = 0
# loop to publish the velocity estimate, current_distance = velocity * (t1 - t0)
while (i <= time):
# Publish the velocity
self.vel_publisher.publish(self.cmd)
self.summit_vel_publisher.publish(self.cmd)
i += 0.1
self.rate.sleep()
# set velocity to zero to stop the robot
self.stop_robot()
s = "Moved robot " + motion + " for " + str(time) + " seconds"
return s
def turn(self, clockwise, speed, time):
# Initilize velocities
self.cmd.linear.x = 0
self.cmd.linear.y = 0
self.cmd.linear.z = 0
self.cmd.angular.x = 0
self.cmd.angular.y = 0
if clockwise == "clockwise":
self.cmd.angular.z = -speed
else:
self.cmd.angular.z = speed
i = 0
# loop to publish the velocity estimate, current_distance = velocity * (t1 - t0)
while (i <= time):
# Publish the velocity
self.vel_publisher.publish(self.cmd)
self.summit_vel_publisher.publish(self.cmd)
i += 0.1
self.rate.sleep()
# set velocity to zero to stop the robot
self.stop_robot()
s = "Turned robot " + clockwise + " for " + str(time) + " seconds"
return s
def rotate(self, degrees):
time.sleep(1)
target_rad = (degrees * math.pi/180) + self.yaw
if target_rad < (- math.pi):
target_rad = target_rad + (2 * math.pi)
if target_rad > (math.pi):
target_rad = target_rad - (2 * math.pi)
while abs(target_rad - self.yaw) > 0.01:
self.cmd.angular.z = 0.5 * (target_rad - self.yaw)
self.vel_publisher.publish(self.cmd)
self.rate.sleep()
self.stop_robot()
if __name__ == '__main__':
#rospy.init_node('robot_control_node', anonymous=True)
robotcontrol_object = RobotControl()
try:
robotcontrol_object.move_straight()
except rospy.ROSInterruptException:
passHi @ziga.rupret,
-
def __init___is the code that runs when a Python class is instantiated (when an instance of the class is created). -
rospy.init_nodeis required for any ROS Python node (you will learn more about this if you take the Basic ROS course). - Usually you “init” a node at the beginning of the code, so the
def __init__of a class is a good place to do that.