ros学习
正在学习《ROS机器人程序设计》，随手做一些笔记
在练习到第二章example1_a，example1_b的例子时遇到一些问题。
第一是编译时bin文件夹中始终不出现可执行文件。这时候要注意终端里的提示。按照提示我发现是cpp文件写错了（照书上抄错了。。。），改正之后就可以了。
第二是注意你电脑中的实际信息更改书上的例子，因为版本不同，我的是indigo，书上安装的是Electric和Fuerte，给出的运行命令是
$ rosrun chapter2_tutorials example1_a
$ rosrun chapter2_tutorials example1_b$ rosrun chapter2_tutorials chap2_example1_a
$ rosrun chapter2_tutorials chap2_example1_b第三，按照书上给的命令试了一下，做一下对比和记录
一直在输出[ INFO] [1514033247.919887063]: I heard: [I am the example1_a node]就是example1_b在运行，按ctrl+c跳出就是停止了。根据example1_b是否正在运行分情况分别输入命令。
终端输入命令
$ rosnode list/example1_a
/example1_b
/rosout/example1_a
/rosout可以看出节点列表里确实已经没有exaple1_b了。
终端输入命令
$ rosnode info /example1_aNode [/example1_a]
Publications:
* /message [std_msgs/String]
* /rosout [rosgraph_msgs/Log]
Subscriptions: None
Services:
* /example1_a/set_logger_level
* /example1_a/get_loggers
contacting node http://mawanyu-TM1607:43111/ ...
Pid: 16818
Connections:
* topic: /rosout
* to: /rosout
* direction: outbound
* transport: TCPROS
* topic: /message
* to: /example1_b
* direction: outbound
* transport: TCPROSNode [/example1_a]
Publications:
* /message [std_msgs/String]
* /rosout [rosgraph_msgs/Log]
Subscriptions: None
Services:
* /example1_a/set_logger_level
* /example1_a/get_loggers
contacting node http://mawanyu-TM1607:43111/ ...
Pid: 16818
Connections:
* topic: /rosout
* to: /rosout
* direction: outbound
* transport: TCPROS可以看出最后少了一个topic，节点example1_a的信息里记录了信息的流向，即信息有没有被example1_b接收。虽然example1_b是否接收了信息对example1_a并没有影响，但是信息确实是被记载了（就像你拿了别人的东西被主人看到了。。。）
终端输入命令
$ rosnode info example1_bexample1_b在运行，输出
Node [/example1_b]
Publications:
* /rosout [rosgraph_msgs/Log]
Subscriptions:
* /message [std_msgs/String]
Services:
* /example1_b/get_loggers
* /example1_b/set_logger_level
contacting node http://mawanyu-TM1607:40131/ ...
Pid: 17193
Connections:
* topic: /rosout
* to: /rosout
* direction: outbound
* transport: TCPROS
* topic: /message
* to: /example1_a (http://mawanyu-TM1607:43111/)
* direction: inbound
* transport: TCPROSNode [/example1_b]
Publications: None
Subscriptions: None
Services: None
cannot contact [/example1_b]: unknown nodeexample1_b 也记录了信息是从example1_a那里得到的。而且节点停止之后直接就不被识别的。
终端输入命令
$ rostopic list这条就和可执行文件没关系了，输出
/message
/rosout
/rosout_agg终端输入命令
$ rostopic info /messageexample1_b在运行，输出
Type: std_msgs/String
Publishers:
* /example1_a (http://mawanyu-TM1607:39109/)
Subscribers:
* /example1_b (http://mawanyu-TM1607:35523/)Type: std_msgs/String
Publishers:
* /example1_a (http://mawanyu-TM1607:39109/)
Subscribers: None终端输入命令
$ rostopic bw /message输出
subscribed to [/message]
average: 289.01B/s
mean: 28.00B min: 28.00B max: 28.00B window: 10
average: 284.36B/s
mean: 28.00B min: 28.00B max: 28.00B window: 20
average: 282.78B/s
mean: 28.00B min: 28.00B max: 28.00B window: 30
average: 282.00B/s
mean: 28.00B min: 28.00B max: 28.00B window: 40
average: 281.53B/s
mean: 28.00B min: 28.00B max: 28.00B window: 50
average: 281.23B/s
mean: 28.00B min: 28.00B max: 28.00B window: 60
average: 281.01B/s
mean: 28.00B min: 28.00B max: 28.00B window: 70
average: 280.84B/s
mean: 28.00B min: 28.00B max: 28.00B window: 80
average: 280.71B/s
mean: 28.00B min: 28.00B max: 28.00B window: 90
average: 280.61B/s
mean: 28.00B min: 28.00B max: 28.00B window: 100
average: 280.58B/s
mean: 28.00B min: 28.00B max: 28.00B window: 100
average: 280.55B/s
mean: 28.00B min: 28.00B max: 28.00B window: 100
average: 280.52B/s
mean: 28.00B min: 28.00B max: 28.00B window: 100
average: 280.49B/s
mean: 28.00B min: 28.00B max: 28.00B window: 100