[ros2 basics] Introduction to navigation2 navigation system

Navigation2 The overall architecture

Be careful ： The following explanation is based on Navigation2 v1.0.12 To carry out . Their corresponding ROS2 Version is Galactic.

​

Nav2 The following tools are available ：

● load 、 Tools for providing and storing maps （ Map server Map Server）

● A tool for locating robots on a map (AMCL)

● Avoid obstacles from A Point to move to B Point path planning tool （Nav2 Planner）

● A tool that controls a robot while following a path （Nav2 Controller）

● A tool for converting sensor data into cost map representation in the robot world （Nav2 Costmap 2D）

● Tools for building complex robot behaviors using behavior trees （Nav2 Behavior trees and BT Navigator）

● A tool for calculating recovery behavior in the event of a failure （Nav2 Recoveries）

● Tools to follow sequential waypoints （Nav2 Waypoint Follower）

● Tools and watchdog for managing the server lifecycle (Nav2 Lifecycle Manager)

● A plug-in that enables user-defined algorithms and behaviors （Nav2 Core）

Navigation2 Compare with Navigation1 There have been great changes . One of the most significant changes is the use of behavior trees to combine various functional modules , To achieve the development effect of Lego building blocks .

Navigation1 The implementation of the navigation function in is pipelined , Mainly by move_base To combine the functions of each module . stay move_base A state machine is implemented in , Both the global path planner and the local path planner are called in the corresponding state in the form of plug-ins . A point-to-point navigation process is , First, call the global path planner in a state , Then it enters another state and passes the path to the local path planner , And make it execute the path .

stay Navigation2 in , The organization of each function is different . The global path planning function is implemented by each global path planning plug-in , These plug-ins are loaded into Planer Server in . Through the corresponding action towards Planer Server Request global planning path .

Empathy , The local path planner is also implemented in the form of plug-ins . They have a unified interface , Can be loaded into Controller Server in . When a path needs to be executed , Just go through the corresponding action Send the path to execute to Controller Server that will do .

Smart you , I should have thought of .Recovery Server It also works with the same logic .

Planer Server 、 Controller Server and Recovery Server Realized their respective functions , Global path planning , Local path planning and recovery operations . But their functions are independent , non-interfering . To achieve a complete navigation function requires the cooperation of each module .BT Navigator Server The one who assembled Lego blocks .

Each function is a behavior tree . The nodes in this tree will be linked to Planer Server 、 Controller Server and Recovery Server signal communication , Put each server The functions of . For example, the single point navigation function , The corresponding node in the behavior tree will be directed to Planer Server Request a planned path to the target point . Then another node in the tree is connected to Controller Server signal communication , Send the planned path to Controller Server To carry out . Of course, this is just a brief description of the process , More functions can be combined in actual use .

When BT Navigator Server The function of single point navigation is realized in , It is logical to realize multi-point navigation .Waypoint Follower Through continuous BT Navigator Server Multi point navigation can be realized by requesting the single point navigation function . When the previously requested single point navigation is completed , Then send the next single point navigation request . Until all points have been issued .

On the periphery of the above block diagram map、Sensor Data and Tf Is the common data . Each functional module can obtain , Just use it as needed .

Navigation2 First experience

1. install Navigation2

You can refer to my previous article to operate .

https://shoufei.blog.csdn.net/article/details/124394203

2. start-up gazebo

ros2 launch turtlebot3_gazebo turtlebot3_world.launch.py

3. Start navigation

ros2 launch turtlebot3_navigation2 navigation2.launch.py use_sim_time:=True 

Navigation2 Relevant introduction materials

Official documents ：

https://navigation.ros.org/getting_started/index.html

Navigation2 official github：

Among them issue The discussion is worth watching

https://github.com/ros-planning/navigation2

Navigation2 Corresponding papers ：

https://arxiv.org/pdf/2003.00368.pdf

Navigation 2 Series of tutorials ：

https://zhuanlan.zhihu.com/p/384099348

at present Navigation2 Plug in provided ：

https://navigation.ros.org/plugins/index.html#plugins

---

If you think it's useful, just praise it ！

It's me , One to help everyone Filling pit Robot development siege lion .

In addition, the official account. 《 First flight 》 Internal reply “ robot ” Get carefully recommended C/C++,Python,Docker,Qt,ROS1/2 And other commonly used technical data in the robot industry .