2021-07-18 ROS笔记－基础和通讯

我的ROS是noetic版，语言是Python，Ubuntu是20.04
下面说一些遇到过的坑，以及一些经验

关于Linux的简单使用

创建文件

这样比较方便

>>1.py
echo "int a">>1.py

还可以用vim等

创建文件夹

mkdir <name>

移动

mv [option]  <source>  <target>

其中[option] -f 是强制
-i 是会问你要不要

删除

rm [option] <name>

其中[option] -f 是强制
-i 是会问你要不要
-r 是递归删除所有子文件

拷贝

cp <source> <target>

换行

\

关于配置环境

创建功能包

因为功能包的结构比较固定，所以建起来麻烦，需要直接调用系统命令

cd ~/catkin_ws/src
catkin_create_pkg <name> [depend1] [depend2] [depend3]

编译工作空间和设置环境变量

cd ~/catkin_ws
catkin_make
. ./devel/setup.bash或source ./devel/setup.bash

注意：这里的环境变量只在当前终端有效，如果希望环境变量在所有终端有效

echo "source /WORKSPACE/devel/setup.bash">>~/.bashrc

WORKSPACE表示工作空间路径

小知识：在linux里，~表示home，／表示根目录

查看工作位置

echo $ROS_PACKAGE_PATH

小知识：$通常在程序里表示变量

关于Python脚本

有些python脚本是不带后缀.py的，而有些是带的，用的时候要看清楚 不然会报错

修改默认Python版本

ROS相关库默认安装在Python3下面，而Ubuntu默认打开的版本是python2，需要如下修改

echo alias python=python3 >> ~/.bashrc

并立即执行

. ~/.bashrc

其中alias是表示等价命令
.bashrc是系统的隐藏文件，用于用户的自定义命令，对所有的命令行窗口都会生效

关于包里的代码在哪和roscp使用的说明

写在包目录下的scripts文件夹的自定义文件 可以直接被这样运行

rosrun beginner_tutorials talker.py

而包自带的文件在比如/opt/ros/noetic/share/rospy_tutorials/005_add_two_ints里
不可以被直接这样运行

rosrun beginner_tutorials add_two_ints_server.py（错）

需要拷出来

roscd beginner_tutorials/
roscp rospy_tutorials add_two_ints_server scripts/add_two_ints_server.py
roscp rospy_tutorials add_two_ints_client scripts/add_two_ints_client.py

roscp可以递归遍历一个文件夹下面所有文件
roscd可以直接cd到一个包里，不需要绝对目录

使用自定义消息

CMakeList里这个命令写在最前面
find_package(catkin REQUIRED COMPONENTS
roscpp
rospy
std_msgs
message_generation
)

然后要写
add_service_files(
FILES
AddTwoInts.srv
)
add_message_files(
FILES
Num.msg
)
generate_messages(
DEPENDENCIES
std_msgs
)
catkin_package(
…
CATKIN_DEPENDS message_runtime …
…)

等

xml文件里下面的去除注释
<build_depend>message_generation</build_depend>
<exec_depend>message_runtime</exec_depend>

在做完相应工作后，python脚本里如下引用即可

from std_msgs.msg import String
from beginner_tutorials.msg import Num 

上面那句是标准消息功能包里的基础消息 String，只包含一个成员，即data，用于存字符串的信息
下面那句是在自定义包beginner_tutorials的msg文件夹里的Num.msg文件
里面写了

int64 num

通信机制介绍

主要有[gugugu]

使用publisher

import rospy
from std_msgs.msg import String

def talker():
    pub = rospy.Publisher('chatter', String, queue_size=10)
    rospy.init_node('talker', anonymous=True)
    rate = rospy.Rate(10) # 10hz
    while not rospy.is_shutdown():
        hello_str = "hello world %s" % rospy.get_time()#感觉%s和后面的% 可以被替代为+
        rospy.loginfo(hello_str)#打印到屏幕上
        pub.publish(hello_str)
        rate.sleep()#delay
#防止中间退出增强鲁棒性
if __name__ == '__main__':
    try:
        talker()
    except rospy.ROSInterruptException:
        pass

使用 subsriber

import rospy
from std_msgs.msg import String

def callback(data):
    rospy.loginfo(rospy.get_caller_id() + "I heard %s", data.data)#打印到屏幕
    
def listener():

    # In ROS, nodes are uniquely named. If two nodes with the same
    # name are launched, the previous one is kicked off. The
    # anonymous=True flag means that rospy will choose a unique
    # name for our 'listener' node so that multiple listeners can
    # run simultaneously.
    rospy.init_node('listener', anonymous=True)
    # 同一个topic “chatter”下
    rospy.Subscriber("chatter", String, callback)#注册callback作为回调函数

    # spin() simply keeps python from exiting until this node is stopped
    # 防止程序中间退出 增强鲁棒性
    rospy.spin()

if __name__ == '__main__':
    listener()

使用server

#!/usr/bin/env python3
## Simple demo of a rospy service that add two integers

NAME = 'add_two_ints_server'

# import the AddTwoInts service
from rospy_tutorials.srv import *
import rospy 

def add_two_ints(req):
    print("Returning [%s + %s = %s]" % (req.a, req.b, (req.a + req.b)))
    return AddTwoIntsResponse(req.a + req.b)

def add_two_ints_server():
    rospy.init_node(NAME)
    s = rospy.Service('add_two_ints', AddTwoInts, add_two_ints)

    # spin() keeps Python from exiting until node is shutdown
    rospy.spin()

if __name__ == "__main__":
    add_two_ints_server()

另一种写法

#!/usr/bin/env python

from __future__ import print_function

from beginner_tutorials.srv import AddTwoInts,AddTwoIntsResponse
import rospy

def handle_add_two_ints(req):
    print("Returning [%s + %s = %s]"%(req.a, req.b, (req.a + req.b)))
    return AddTwoIntsResponse(req.a + req.b)

def add_two_ints_server():
    rospy.init_node('add_two_ints_server')
    s = rospy.Service('add_two_ints', AddTwoInts, handle_add_two_ints)
    print("Ready to add two ints.")
    rospy.spin()

if __name__ == "__main__":
    add_two_ints_server()

使用client

#!/usr/bin/env python3
## Simple demo of a rospy service client that calls a service to add
## two integers. 

import sys
import os
import rospy
# imports the AddTwoInts service 
from rospy_tutorials.srv import *

## add two numbers using the add_two_ints service
## @param x int: first number to add
## @param y int: second number to add
def add_two_ints_client(x, y):
	# 可以不用initial初始化 因为service不一定要是节点 是随时发起的
    # NOTE: you don't have to call rospy.init_node() to make calls against
    # a service. This is because service clients do not have to be
    # nodes.

    # block until the add_two_ints service is available
    # you can optionally specify a timeout
    rospy.wait_for_service('add_two_ints')
    
    try:
        # create a handle to the add_two_ints service
        add_two_ints = rospy.ServiceProxy('add_two_ints', AddTwoInts) 
        print("Requesting %s+%s"%(x, y))
        
        # simplified style
        resp1 = add_two_ints(x, y)

        # formal style
        resp2 = add_two_ints.call(AddTwoIntsRequest(x, y))

        if not resp1.sum == (x + y):
            raise Exception("test failure, returned sum was %s"%resp1.sum)
        if not resp2.sum == (x + y):
            raise Exception("test failure, returned sum was %s"%resp2.sum)
        return resp1.sum
    except rospy.ServiceException as e:
        print("Service call failed: %s"%e)

def usage():#输出用法
    return "%s [x y]"%sys.argv[0] #argv[0]表示文件名

if __name__ == "__main__":
    
    argv = rospy.myargv()
    if len(argv) == 1:#无输入
        import random
        x = random.randint(-50000, 50000)
        y = random.randint(-50000, 50000)
    elif len(argv) == 3:
        try:
            x = int(argv[1])
            y = int(argv[2])
        except:
            print(usage())
            sys.exit(1)
    else:
        print(usage())
        sys.exit(1)
    print("%s + %s = %s"%(x, y, add_two_ints_client(x, y)))

另一种写法

#!/usr/bin/env python

from __future__ import print_function

import sys
import rospy
from beginner_tutorials.srv import *

def add_two_ints_client(x, y):
    rospy.wait_for_service('add_two_ints')
    try:
        add_two_ints = rospy.ServiceProxy('add_two_ints', AddTwoInts)
        resp1 = add_two_ints(x, y)
        return resp1.sum
    except rospy.ServiceException as e:
        print("Service call failed: %s"%e)

def usage():
    return "%s [x y]"%sys.argv[0]

if __name__ == "__main__":
    if len(sys.argv) == 3:
        x = int(sys.argv[1])
        y = int(sys.argv[2])
    else:
        print(usage())
        sys.exit(1)
    print("Requesting %s+%s"%(x, y))
    print("%s + %s = %s"%(x, y, add_two_ints_client(x, y)))

写完py文件后的配置

添加权限使其被标记为可执行

chmod +x scripts/add_two_ints_server.py

对于这个命令的解释，详见https://blog.csdn.net/u012106306/article/details/80436911

然后在CMakeList文件里添加

catkin_install_python(PROGRAMS scripts/add_two_ints_server.py
  DESTINATION ${CATKIN_PACKAGE_BIN_DESTINATION}
)

确保安装正确脚本和使用正确的解释器

rosbag 对通信的记录和回放

rostopic list -v

显示正在使用的主题

cd ~/bagfiles
rosbag record -a 

a表示all

rosbag record /topic_name1 /topic_name2 /topic_name3

对感兴趣的topic记录，topic的表示是斜杠加topic名

rosbag record -O filename.bag /topic_name1

指定文件名