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Why map frame is not continuous?

asked 2012-02-02 02:27:00 -0500

sam gravatar image

updated 2014-01-28 17:11:15 -0500

ngrennan gravatar image

In rep-0105,it says "The map frame is not continuous, meaning the pose of a mobile platform in the map frame can change in discrete jumps at any time."

In my opinion, the map frame (on navigation application) is a global coordinate,its three axis is continuous, and the robot pose on that coordinate can be change over time.

Is that right?

Thank you~

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answered 2012-02-02 02:37:13 -0500

Thomas gravatar image

updated 2012-02-02 22:53:06 -0500

The map frame is the result of a localization node. Typical global localization algorithms such as SLAM for instance are absolute but movements in the map frame is not continuous due to sensor noise for instance.

Therefore, it is better not to inject them directly into the robot command. On the opposite, the odometry provided by the PR2 wheel encoders for instance are continuous but is less and less precise over time. See robot_pose_ekf for instance as a way to merge both strategies.

So yes you are right, the map frame provide a global position of the robot base link. However, depending on your localization algorithm this position may "jump".

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So map frame(a coordinate) is fixed not move or change by SLAM or localization node, and the only moved thing is the robot pose,right?
sam gravatar image sam  ( 2012-02-02 02:49:09 -0500 )edit
It would be better to word it as "Movement in the map frame is not continuous."
tfoote gravatar image tfoote  ( 2012-02-02 15:58:10 -0500 )edit
map is a frame which does not move. The transformation linking map to base_link changes over time and is updated by a localization node.
Thomas gravatar image Thomas  ( 2012-02-02 22:55:34 -0500 )edit

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Asked: 2012-02-02 02:27:00 -0500

Seen: 266 times

Last updated: Feb 02 '12