ROS Twist和Odometry消息类型使用（Python）

<div class="blogpost-body" id="cnblogs_post_body">
消息类型：
<h3>1. Twist - 线速度角速度</h3>
通常被用于发送到/cmd_vel话题，被base controller节点监听，控制机器人运动
<div class="cnblogs_code">
 <pre class="blockcode">geometry_msgs/Twist

geometry_msgs/Vector3 linear
float64 x
float64 y
float64 z
geometry_msgs/Vector3 angular
float64 x
float64 y
float64 z</pre>
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linear.x指向机器人前方，linear.y指向左方，linear.z垂直向上满足右手系，平面移动机器人常常linear.y和linear.z均为0
angular.z代表平面机器人的角速度，因为此时z轴为旋转轴
示例：
<div class="cnblogs_code">
 <pre class="blockcode">#! /usr/bin/env python
'''
Author: xushangnjlh at gmail dot com
Date: 2017/05/22

@package forward_and_back
'''
import rospy
from geometry_msgs.msg import Twist
from math import pi

class ForwardAndBack():
 def __init__(self):
rospy.init_node('forward_and_back', anonymous=False)
rospy.on_shutdown(self.shutdown)
# this "forward_and_back" node will publish Twist type msgs to /cmd_vel 
# topic, where this node act like a Publisher 
self.cmd_vel = rospy.Publisher('/cmd_vel', Twist, queue_size=5)

# parameters
rate = 50
r = rospy.Rate(rate)

linear_speed = 0.2
goal_distance = 5
linear_duration = goal_distance/linear_speed

angular_speed = 1.0
goal_angular = pi
angular_duration = goal_angular/angular_speed

# forward->rotate->back->rotate
for i in range(2):
 # this is the msgs variant, has Twist type, no data now
 move_cmd = Twist()

 move_cmd.linear.x = linear_speed #
 # should keep publishing
 ticks = int(linear_duration*rate)
 for t in range(ticks):
 # one node can publish msgs to different topics, here only publish
 # to /cmd_vel
 self.cmd_vel.publish(move_cmd)
 r.sleep # sleep according to the rate

 # stop 1 ms before ratate
 move_cmd = Twist()
 self.cmd_vel.publish(move_cmd)
 rospy.sleep(1)

 move_cmd.angular_speed.z = angular_speed
 ticks = int(angular_duration*rate)
 for t in range(ticks):
 self.cmd_vel.publish(move_cmd)
 r.sleep()

self.cmd_vel.publish(Twist())
rospy.sleep(1)

 def shutdown(self):
rospy.loginfo("Stopping the robot&#