Understanding of Odom coordinate system

ROS Understanding of the basic coordinate system in ：map,odom,base_link,base_laster

1.map

Map coordinate system , seeing the name of a thing one thinks of its function , Generally, the coordinate system is set as a fixed coordinate system , Generally, it coincides with the world coordinates of the robot .

2.base_link

Robot body coordinate system , Coincide with the center of the robot , Of course, some robots are base_footprint.

3.odom

Odometer coordinate system , The main distinction here is odom topic, These are two concepts , One is the coordinate system , One is the odometer information calculated according to the coded odometer . But there is also a relationship ,odom topic The transformed pose matrix is odom->base_link Of tf Relationship . There may be questions ：

① The pose matrix should not be map->base_link Of tf Does it matter ？
②map Coordinate system and odom What does the coordinate system matter ？

In fact, when the robot first started to move ,odom Coordinate system and map The coordinate system is coincident , namely odom->base_link And map->base_link Of tf It's consistent .
But over time , There's a deviation , The deviation that occurs is the cumulative error of the odometer , If the odometer is very accurate , No calculation error , that map Coordinate system and odom The coordinate system will always be coincident .

But in reality , Odometer is biased , So the pose matrix we get by calculating the odometer is odom->base_link, And map->base_link There are still deviations .

③ that map->odom Of tf How did you get it ？

Apart from the odometer, there are also some sensors for cooperative calibration, such as imu, These sensors can estimate the position of the robot in the map, that is map->base_link Of tf, We estimate the deviation between the robot's position in the map and the position obtained by the odometer, that is map->odom Of tf.

4.base_laser

Lidar coordinate system , It is related to the installation point of laser radar , It is associated with base_link Of tf Is constant .

Summary

Recently in to see tf Knowledge about , I will take the time to sum up a little later , Let's refuel and rush together , Have a nice weekend ！