Include option to use PointCloud Transport

[SteveMacenski]

Per https://github.com/ros-perception/point_cloud_transport, we can now use compressed pointcloud streams in ROS 2. We can enable those in the Costmap layers that ingest pointcloud sensor streams (i.e. obstacle, voxel) and the collision monitor and show that this reduces network traffic without composed nodes to keep up better (and CPU impacts).

We would want sensor drivers and depth pipelines to have the option to output this as well to be able to ingest in Nav2 out of the box. Rviz2 + Gazebo would be ideal as well to publish PC2 from Gazebo into Rviz without as much latency

CC @ahcorde

[Combuster54]

Hi, could you provide more info? I would like to contribute if it´s possible.

[xFranv8]

I'm taking this issue. Thanks!

[SteveMacenski]

@xFranv8 any updates?

[elsayedelsheikh]

I think we have a similar case to image_transport package, where image_transport and point_cloud_transport don't have LifecycleNode support

• [ROS2] image_transport does not support LifecycleNode ros-perception/image_common#108
• Support lifecycle node ros-perception/image_common#304

https://github.com/ros-perception/image_common/blob/b021202a42d7bc3ff3215237ded251a59c282da5/image_transport/include/image_transport/publisher.hpp#L72-L77

https://github.com/ros-perception/point_cloud_transport/blob/0350a390bdd8cc39c509b71614a4c613457ce909/point_cloud_transport/include/point_cloud_transport/publisher.hpp#L59-L64

Should we wait till it gets implemented in point_cloud_transport? or/ work around it?

[SteveMacenski]

Do they need lifecycle support if we create them in the configure / activate methods of our lifecycle servers? Note in Costmap2D we use Message Filters, which has an unsubscsribe/subscribe option -- I'm not sure if/how you can or should use both message filters and image / PC2 transport, but I imagine you can by daisy chaining callbacks. If so, then that unsubscribe/subscribe feature would give you virtual lifecycle support for our needs here, even if not supported by those libraries.

Optionally: you could choose to implement it in the transport pipelines as part of this ticket, I'm sure the maintainers would love the help and further have impact in the community! But, I don't think it is largely necessary, since the transports are used within costmap layers or within operations that themselves are happening in lifecycle transitions. We don't try to make the subscribers until we're in the configure state (though between configure and activate... the message filters subscribe resolves that for us for now -- if we can daisy chain and use both; don't return callback until a TF transform exists and use the compression pipelines)

[elsayedelsheikh]

Perfect!
Moving on with PCL Transport SubscriberFilter variant for the Obstacle layer
Thanks :)

Edit:

TODO:

Pre

• Add LifecycleNode support to point_cloud_transport using template based approach similar to message_filter
  Feat/Add LifecycleNode Support ros-perception/point_cloud_transport#109

Main

• obstacle_layer/voxel_layer plugins
• STVL/NPVL plugins
• collision_monitor node

Performance Evaluation

Metrics ? (Bandwidth/DataQuality/Frequency/Latency/CPU&MemoryUsage)

Wrap-up

• Documentation update: transport method with default "raw"
• Migration guide
• Quick tutorial on usage

[SteveMacenski]

Conveniently, the voxel layer uses the obstacle layer's base for subscriptions, so its a 2 for 1!

I think also STVL/NPVL would be good as well, while you're at it!

Add transport method parameter with "raw" as default ?

I think that would be good

Also add into your tasks for documentation updates to the layer's configuration file, migration guide, and best yet if you wanted to write a quick tutorial about how to use it (and some metrics about how it improves performance - possibly?)

[DasariChaitanya]

Hi everyone,

I've been working on this topic for a few days now and didn't realize others were also on it. I should have posted earlier. I have not noticed there's a Subscribe Filter variant in PCL transport that might be a better implementation than what I'm currently using.

@elsayedelsheikh, let me know if you'd like any assistance.

[elsayedelsheikh]

Sounds good!

@DasariChaitanya
Let’s catch up on the progress and work on this together - there’s a lot to do/test.
Hopefully, we can wrap it up by next weekend! 💯

Edit:
For the publishers, which are you following?

1. Use all available transports for output
2. Load specific transport plugin

Check point_cloud_transport_republisher

One additional PointCloud2 publisher in nav2_dwb_controller which publishes the CostGrid

navigation2/nav2_dwb_controller/dwb_core/include/dwb_core/publisher.hpp

Line 127 in 6e1c85e

std::shared_ptr<LifecyclePublisher<sensor_msgs::msg::PointCloud2>> cost_grid_pc_pub_;