ros 学习笔记 （三）：入门学习_lerion@lerion-virtual-machine:~/catkin_ws/src$ ros

创建工作空间和功能包

1. 创建工作空间

//建立目标文件夹
chenxiya@chenxiya-virtual-machine:~$ mkdir catkin_ws
//进入
chenxiya@chenxiya-virtual-machine:~$ cd catkin_ws
//建立 src 文件夹 
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ mkdir src
//进入
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ cd src/
//初始化工作空间
chenxiya@chenxiya-virtual-machine:~/catkin_ws/src$ catkin_init_workspace
Creating symlink "/home/chenxiya/catkin_ws/src/CMakeLists.txt" pointing to "/opt/ros/melodic/share/catkin/cmake/toplevel.cmake"
//返回工作空间根目录
chenxiya@chenxiya-virtual-machine:~/catkin_ws/src$ cd ..
//使用 pwd 查看路径
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ pwd
/home/chenxiya/catkin_ws
//使用 catkin_make 编译
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ catkin_make
----结果
Base path: /home/chenxiya/catkin_ws
Source space: /home/chenxiya/catkin_ws/src
Build space: /home/chenxiya/catkin_ws/build
Devel space: /home/chenxiya/catkin_ws/devel
Install space: /home/chenxiya/catkin_ws/install
----结果
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至此 一个空的工作空间创立并且初始化结束

2. 创建功能包及设置环境变量

//进入src 文件夹
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ cd src/
//创建功能包 test_pkg  并且添加依赖 roscpp rospy std_msgs
chenxiya@chenxiya-virtual-machine:~/catkin_ws/src$ catkin_create_pkg test_pkg roscpp rospy std_msgs
//创建带 install 文件夹的工作空间
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ catkin_make install
// src 里面是功能包 
//设置工作空间环境变量--- 系统才能找到工作空间的功能包
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ source devel/setup.bash
//使用 echo 打开 检查环境变量
chenxiya@chenxiya-virtual-machine:~/catkin_ws$ echo $ROS_PACKAGE_PATH
/home/chenxiya/catkin_ws/src:/opt/ros/melodic/share
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3. 发布者

#add_executable(velocity_publisher src/learning_topic/src/velocity_publisher.cpp)
/*对比此行上下两句，这里为什么不是绝对路径；*/
add_executable(velocity_publisher src/velocity_publisher.cpp)
/*
这里费了老大的劲，
*/
target_link_libraries(velocity_publisher  ${catkin_LIBRARIES})
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此前错误一：找不到，把上面的路径修改就可以了；

-- Configuring done
CMake Error at learning_topic/CMakeLists.txt:154 (add_executable):
  Cannot find source file:
  
    src/learning_topic/src/velocity_publisher.cpp

  Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm .hpp
  .hxx .in .txx
CMake Error: CMake can not determine linker language for target: velocity_publisher
CMake Error: Cannot determine link language for target "velocity_publisher".
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接着就可以

问题2

chenxiya@chenxiya-virtual-machine:~$ rosrun lerarning_topic velocity_publisher
[rospack] Error: package 'lerarning_topic' not found
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原因：在同一个终端里面同时进行环境配置和rosrun learning_topic velocity_publisher
解决办法：重新打开一个终端，并且输入

cd ~/catkin_ws
source devel/setup.bash
rosrun learning_topic velocity_publisher
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问题三：设置全局环境变量：

1、根目录下：找到 隐藏文件 （ctrl+h 显示/隐藏文件）

2、在最后添加
原本安装ros的环境变量：

source /opt/ros/melodic/setup.bash
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添加的当前功能包的环境变量：

source /home/chenxiya/catkin_ws/devel/setup.bash
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setup.bash的文件路径 根据自己的文件使用 pwd 命令查看；

最后就可以再任意路径下发布功能包：

4. 订阅者

流程：

5. 话题消息的定义和使用

6. ros中的坐标管理系统

操作

chenxiya@chenxiya-virtual-machine:~$ roslaunch turtle-tf turtle_tf_demo.launch
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错误表现：

RLException: [turtle_tf_demo.launch] is neither a launch file in package [turtle-tf] nor is [turtle-tf] a launch file name
The traceback for the exception was written to the log file
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解决：roslaunch turtle-tf turtle_tf_demo.launch
改为 roslaunch turtle_tf turtle_tf_demo.launch

查看tf树坐标工具

 rosrun tf view_frames 
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rosrun tf tf_echo turtle1 turtle2
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rosrun rviz rviz -d `rospack find turtlef`/rviz/turtle_rviz.rviz
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chenxiya@chenxiya-virtual-machine:~$ rostopic list
/cmd_vel
/person_info
/rosout
/rosout_agg
/turtle1/color_sensor
/turtle1/pose
chenxiya@chenxiya-virtual-machine:~$ rost
rostest   rostopic  
chenxiya@chenxiya-virtual-machine:~$ rostopic pub -r 10 /turtle1/
/turtle1/color_sensor  /turtle1/pose          
chenxiya@chenxiya-virtual-machine:~$ rostopic pub -r 10 /turtle1/
/turtle1/color_sensor  /turtle1/pose          
chenxiya@chenxiya-virtual-machine:~$ rostopic pub -r 10 /turtle1/pose turtlesim/Pose "{x: 1.0, y: 1.0, theta: 0.0, linear_velocity: 0.0, angular_velocity: 0.0}" 

^[[A^[[D^[[D^[[B^[[A^Cchenxiya@chenxiya-virtual-machine:~$ rostopic pub -r 10 /tPose "{x: 1.0, y: 1.0, theta: 0.0, linear_velocity: 1.0, angular_velocity: 1.0}" 

chenxiya@chenxiya-virtual-machine:~$ rostopic pub /cmd_vel geometry_msgs/Twist "linear:
  x: 1.0
  y: 0.0
  z: 0.0
angular:
  x: 0.0
  y: 0.0
  z: 0.0" 
publishing and latching message. Press ctrl-C to terminate
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