I need to know the detail of the frames of the Cartographer. Please check my understanding.
I have read ‘REP 105 -- Coordinate Frames for Mobile Platforms (ROS.org)’, and ‘Setting Up Transformations — Navigation 2 1.0.0 documentation’, and ‘(new user link limit:discourse.ros.org/t/map-base-odom-as-alternative-for-rep-105-recommended-frame-order/25095/5.’
The basic relationship between ROS frames can be represented by the following figure.
Since the SLAM can draw a map, using some number to represent the object of the world, the object shod be placed in the frame ‘map.’ Meanwhile, it can locate the robot, so the robot’s pose should be also represented in ‘map.’
A robot is an object, rather than an ideal point in the world. So, if the SLAM wants to locate the robot, it should locate which part of the robot. Is it the robot’s head or its foot? The Cartographer algorithm suggests using the link where the IMU is installed. Good choice! This is usually the stable part of a robot.
This is strange!
Is it more direct if we use the same part that an odometry system is used to track the robot, e.g., the frame ‘base_link.’
I do not fully understand this frame. I think the algorithm should publish TF information, which should be the relation between the frame ‘map’ to the frame ‘odom’. However, if the robot does not have an odometry system, the TF should directly connect ‘map’ to ‘base_link.’
This is strange!
Why not directly connect the frame ‘map’ to the ‘tracking_frame.’ Since this robot does not have an odometry system.
Is it the name of the odometry system’s frame?
provide_odom_frame = false, but use_odometry = true ???
The robot does not provide an odometry system because it can not provide an odometry frame. How can we use odometry? It cannot subscribe to the weel coder information, and it does not know the structure of the robot.
The session is too short. I have to re-enter the lecture, again and again, each time I finish reading a part of the lecture.