RTAB-MAP&RVIZ TOOL Localization

[CGV_Kwak]

Hi Matthue.
While I was trying localization mode, there was some issue.

When I was mapping, if I went same area and see the same feature, the loop closure's color was green.

But after I tried to localization mode, we set the robot in the same area and see the same feature a lot of times, the rtabmap's loop closure color was only yellow. However, in the 3D View the path was showed with pink dot's and line(node and link). Also in the rviz tool, localization was succeeded and the robot's location was printed in 2d map.

By this situation I have some question.

During mapping mode the Loop Closure's color was green. But in the localization mode, the color was always yellow, path was shown in 3d view( pink) and location was printed in rviz tool.

Why does it shown only yellow color in localization mode? Is there any special reason? localization failed? Then, why in the rviz tool found the location?

Maybe we guess by 2 things.
1. We changed URDF file robot's camera location. We guess this strongly because before we changed the URDF file and made a db. By this DB file, the issues doesn't happen.
2. TF error?
3. localization code error?

Thanks.

[matlabbe]

Hi,

Are you also using a lidar? Yellow loop closures are proximity detections, which act like loop closures but are found by proximity to the current location. The pink path are the nodes corresponding to the localization session.

Green loop closures are those found with the camera. Changing the URDF is fine when attaching the camera to another place on the robot, though doing so the point of view may have changed, adding more difficulty to detect visual loop closures (green). If you have a lidar, maybe the lidar proximity detection was taking over instead. So yes, it could be indeed a problem if the camera cannot be used to find visual loop closures anymore. While lidar proximity detection can work when the robot is already roughly localized, it cannot handle the "kidnapped robot problem" like visual loop closure detection does.

See also https://github.com/introlab/rtabmap/discussions/1575#discussioncomment-14357237 for the color code.