简介
ROS (The Robot Operating System) 是一个灵活的机器人研发的框架。
机器人运行逻辑：Computer Vision + Sensor Fusion -> Localization -> Path Planning -> Control
优点
- Modularity: 每个功能都可以作为单独的程序运行。
- Distributed: programs can run on multiple computers across different networks
- Reproducible: 软件复用率高
- 很多机器人功能都是开源
- 提供 interface/API for both Python and C++
ROS Workspace
folders to host, modify, and update all the components of a robotic system in one place. 形式如下：
workspace_folder/ -- WORKSPACE
src/ -- SOURCE SPACE
CMakeLists.txt
package_1/
CMakeLists.txt
package.xml
...
package_n/
CATKIN_IGNORE -- optional empty file to exclude package_n from being processed
CMakeLists.txt
package.xml
build/ -- BUILD SPACE
devel/ -- DEVELOPMENT SPACE
install/ -- INSTALL SPACE
创建 ROS 工作空间
$ mkdir -p ~/catkin_ws/src
$ cd ~/catkin_ws/
$ catkin build
$ source devel/setup.bash
Remember to source the workspace every time when you start to use ROS
ROS Packages
A package might contain ROS nodes, a ROS independent library, a dataset, configuration files, …
软件包必须包含
- 一个符合catkin规范的package.xml文件
- 一个catkin版本的CMakeLists.txt文件
workspace_folder/
src/
package/
CMakeLists.txt
package.xml -- dependency to build a package
src/
scripts/
launch/
plans/
test/
include/
config/
创建 ROS
$ cd ~/catkin_ws/src
$ catkin_create_pkg <pkg_name> std_msgs rospy roscpp [more_depends]
$ catkin build
$ source devel/setup.bash
Navigating ROS Filesystem
rospack: get information about packages.
$ rospack fine [package_name]
roscd: change directory directly to a package or a stack.
$ roscd <package> [/subdir]
rosls: list directly in a package by name rather than by absolute path.
$ rosls [package_name]
ROS Communication Graph
一个process (pkg1) 调用摄像头，另一个process (pkg2) 识别人，ROS通过 graph-like structure 管理各个processes之间的通信。
Basic ROS Graph Components:
- Nodes
- Topics
- Messages
- Services
- Bags
- Parameter Server
- Master
Nodes
定义：Nodes are the executables that take care of computation
Nodes can interact with each other, and they are implemented by ROS client libraries like roscpp or rospy
run a node use rosrun
Topics
named routes over which nodes exchange messages. Each route have a specific topic name associated with it.
Msg
Nodes communicate with each other by publishing messages to topics.
A message is a simple data structure comprising typed fields
geometry_msgs/Point.msg
float64 x
float64 y
float64 z
Publisher and Subscriber
Publisher (Pub): a node that publishes a specific type of message over a given topic.
Subscriber (Sub): a node that subscribes a specific type of message over a given topic and invokes a callback function to process received message.
Pub/Sub is a form of asynchronous communication
Parameter Server
a shared dictionary used by nodes to store and retrieve parameters at runtime
rosparam list # list all parameters' name
rosparam get <param-name> # get parameter's value
rosparam set <param-name> # set parameter to a value
rosparam delete <param-name> # delete a parameter
Master
Responsible for communication between the nodes and maintain registries for nodes and helps them find each other
roscore: command to start the master, and create the communication for ROS nodes.
Remember to run roscore first! The master should always be running when using ROS
Bags
recording from and playing back to ROS topics
rosbag record [TOPIC NAME]
rosbag play [bagfile]
rosbag play --clock [bagfile]