Improve topic naming for better module partitioning

[VRichardJP]

I have observed that modules input/output topics are not always clearly defined/identifiable.

For example in sample_sensor_kit_launch, the lidar preprocessing pipeline generates pointclouds over the following pipeline:

1. /sensing/lidar/*/pointcloud_raw*
2. /sensing/lidar/*/self_cropped/pointcloud*
3. /sensing/lidar/*/mirror_cropped/pointcloud*
4. /sensing/lidar/*/rectified/pointcloud*
5. /sensing/lidar/*/outlier_filtered/pointcloud*
6. /sensing/lidar/concatenated/pointcloud

Without reading the code, it is difficult to guess that /sensing/lidar/top/outlier_filtered/pointcloud* is the output of the pipeline for the top lidar sensor.

Because the pipeline output topic is currently the topic name of the last filter in the pipeline, it forces other modules to refer to the "filter output" instead of the "pipeline output". For example, the localization module explicitly refers to /sensing/lidar/top/rectified/pointcloud, while the perception module refers to /sensing/lidar/concatenated/pointcloud and the obstacle segmentation refers to /sensing/lidar/*/outlier_filtered/pointcloud

Beside the fact the localization module does not even use the last topic of the pipeline, this design breaks modularity: if I change the lidar preprocessing pipeline, I will have to modify many other modules as well.

One simple solution is to keep a consistent topic naming convention across modules. For example, using depth to "hide" detail and intermediate results:

1. /sensing/lidar/top/raw/pointcloud
2. /sensing/lidar/top/filterA/pointcloud
3. /sensing/lidar/top/filterB/pointcloud <- intermediate cloud for top sensor
4. ...
5. /sensing/lidar/top/pointcloud <- top sensor cloud
6. /sensing/lidar/pointcloud <- merged cloud

Here, neither the content of the lidar preprocessing pipeline nor the sensor kit would matter for other modules since they would only refer to /sensing/lidar/top/pointcloud and /sensing/lidar/pointcloud.

I have mostly focused on /sensing/lidar/* related modules, but others may also suffer from similar clarity issue.

[yukkysaito]

Thank you for your suggestion.
I agree with you. Also, in TIER IV, we think it should be changed to the following. It is same as your suggestion.

• /sensing/lidar/(each sensor unique name)/pointcloud <- each sensor point cloud
• /sensing/lidar/pointcloud <- merged cloud

I also had a conversation and suggested the interface topic name to AWF with @mitsudome-r.
However, due to resource constraints, it was left unattended.