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Map and Laser error

asked 2022-06-18 09:27:34 -0500

Os7 gravatar image

Hello all I am facing an issue when trying to navigate, the laser and the saved map data don't match causing some problems when giving a goal location and even when i give a pose there is still a big miss match between them .. how could solve this issue and what might by the cause for it ?
I am using RPlidar that is mounted on top of the robot with a differential drive robot that is getting odom data from two incremental encoders. Here is the map and laser And here is the Rqt graph

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Over time, the odometry pose from your wheel encoders will slowly accumulate error. How are you correcting for this?

Mike Scheutzow gravatar image Mike Scheutzow  ( 2022-06-19 07:29:15 -0500 )edit

I don't know, the problem happens when the robot is rotating when the navigation goal is a straight line it work well

Os7 gravatar image Os7  ( 2022-06-19 07:54:33 -0500 )edit

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answered 2022-06-19 09:38:57 -0500

Mike Scheutzow gravatar image

updated 2022-06-19 09:42:48 -0500

You need to add a new ros node that corrects for the odometry drift. Some people use the ros amcl package for this.

http://wiki.ros.org/amcl

amcl is a Global Localizer. It takes the laser scan and the map as input, and aligns multiple lidar scans to the map to determine the robot's current map pose. Then it publishes a new map->odom transform, which has the effect of correcting any drift in the odom->base_link transform. If I remember correctly, the standard ros amcl node does this calculation only once, so you'll need code to re-trigger the calculation after it finishes.

The reason you need both amcl and wheel-encoder-odom for robot pose is that amcl is slow - it can take more than 1 second for it to decide where the robot is currently.

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I have amcl node running, but from what i have understood from what you said i need to keep re-triggering it like every X seconds? Any idea how i can do this or an example you can refer me to Thanks alot

Os7 gravatar image Os7  ( 2022-06-19 10:14:31 -0500 )edit

The amcl node provides a ros service to do this. Here's how it's used from the command line:

rosservice call /global_localization "{}"

I wouldn't try to do this too often; keep at least a few seconds between calls.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2022-06-19 11:30:12 -0500 )edit

Alright will test this and see how things go thanks for the help

Os7 gravatar image Os7  ( 2022-06-19 11:35:00 -0500 )edit
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Instead of amcl, the laser_scan_matcher can also be used to correct odom drift. It's much faster. Just be aware this is a Tracker, not a Global Localizer.

http://wiki.ros.org/laser_scan_matcher

It's harder to use because it doesn't publish map->odom for you.

Mike Scheutzow gravatar image Mike Scheutzow  ( 2022-06-19 11:39:58 -0500 )edit

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Asked: 2022-06-18 09:27:34 -0500

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Last updated: Jun 19 '22