When using rtabmap to build a map, how to fill the blanks in the map and remove objects outside the map?

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If I use the above 2D method or 3D method, do I have to add a lidar to the robot?

Can I enable ray tracing when only using zed stereo camera, and then configure the above parameters to fill the unknown space?

No, they work also with the depth image of the camera. The map you are seeing is from depth image in 3D by default (without ray tracing). Ray tracing can be enabled with cameras.

How to enable ray tracing with cameras? I refer to zed_nodelet_example and use depthimage_to_laserscan node to convert the depth image generated by the camera into 2D scan. Is this method feasible?

By the way, this example zed_nodelet_example uses nodelet, and I use node. Which one should I choose?

I have enabled ray tracing, and the resulting 2D map has no holes.

We can also convert the depth image to a laser scan, for which RTAB-Map will do ray tracing by default. It is not necessarily though, as if you set parameter Grid/RayTracing to true, it will also do it with depth images. In general, using nodelet is the preferred approach for efficiency. For example, if two nodelets are in the same manager and images should be shared between them, the image topics won't be serialized and deserialized, only a copy of the pointer in memory would be required.

1) According to the above, when I set the parameter Grid / RayTracing to true and Grid / 3D to false, rtabmap convert the depth image to a laser scan. Is it possible for rtabmap to publish sensor_msgs / LaserScan type topics? (By using rostopic find sensor_msgs / LaserScan I did not find the related topic published by rtabmap.)

2) I found two similar parameters gen_scan_max_depth and Grid/RangeMax. I want to know what is the difference between them.

3) The following warning is displayed:

[ WARN] [1588091904.327305697]: /proj_map topic is deprecated! Subscribe to /grid_map topic instead.

What parameters should I set to enable /proj_map topic to be published?

• /proj_map is exactly the same topic than /grid_map. If you need a laser scan topic, use pointcloud_to_laserscan or depthimage_to_laserscan. Rtabmap doesn't republish it, it is actually converted in its local occupancy grid format (all those Grid/ parameters).

• gen_scan_max_depth works with gen_scan argument to rtabmap node, it will make a scan exactly like depthimage_to_laserscan node (the advantage is that it can support multiple cameras to create the scan, assuming the depth cameras are installed like on a rig parallel to ground).

• When using Grid/RayTracing to true and Grid/3D to false, it will do something like pointcloud_to_laserscan, for arbitrarily any 3D point clouds (projecting obstacles to ground then ray tracing to them).