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odom not aligned with base_link?

asked 2018-08-03 14:46:09 -0500

asabet gravatar image

When viewing my robot in rviz, the odom link seems not to be aligned with the rest of the robot . What could causing this?

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Why do you think odom should be lined up with the rest of the robot?

stevejp gravatar image stevejp  ( 2018-08-03 16:03:00 -0500 )edit

Doesn't odometry output the pose of the robot?

asabet gravatar image asabet  ( 2018-08-03 16:04:31 -0500 )edit

I think you have a little misconception between "odometry" and the "odom frame". Googling these terms should get you back on the right path :)

stevemacenski gravatar image stevemacenski  ( 2018-08-04 02:38:36 -0500 )edit

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answered 2018-08-07 04:26:53 -0500

Tom Moore gravatar image

updated 2018-08-07 04:27:17 -0500

The odom frame is a "world-fixed" frame. The (0, 0) point in the odom frame is where your robot was when you started it. So if you turn your robot on, and drive 10 meters forward, then turn left 90 degrees, and then drive 5 meters, your robot's pose in the odom frame is (10, 5) with a yaw/heading of pi/2. The odom frame will not move, because it is "fixed" to the world, and not your robot. The base_link frame is fixed to your robot, so it will move as the robot moves. Note that your robot's pose in the odom frame is equivalent to the odom->base_link transform.

For more information on coordinate frames in ROS, see REP-105.

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To be fair, localization packages like amcl will move the odom frame relative to your world based on scan data. So it's not completely fixed.

pcoenen gravatar image pcoenen  ( 2018-08-07 05:39:39 -0500 )edit

In the context of the question (the image lacks a map frame), it is fixed with respect to the robot's base. You could make the argument that the odom frame moves and the base frame remains fixed, but then I could make the argument that the map frame moves as the odom frame remains fixed.

Tom Moore gravatar image Tom Moore  ( 2018-08-07 06:20:03 -0500 )edit

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Asked: 2018-08-03 14:46:09 -0500

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Last updated: Aug 07 '18