ROS 2 documentation questions

[mjeronimo]

Reading through the ROS 2 documentation, I had the following questions:

Guides/Overriding-QoS-Policies-For-Recording-And-Playback.html

• "Using QoS Overrides" - "Policy values are determined by the policy's short keys, which can be found using ros2topic verbs such as ros2 topic pub --help." What is a "short key?" Also, I don't see from the ros2 topic interface that I can set deadline, lifespan, lifeliness, etc., but those are listed in the YAML file. Can they only be set from the YAML file?

Guides/Node-arguments.html

• "Parameters" - "You can set parameters directly from the command line using the following syntax." The example is running an executable. If that executable has multiple nodes, to which nodes do the parameters apply? I'm supposing it would be all of them. However, if I'm only targeting one of those nodes is there syntax to support that? Shouldn't the parameter names support scoping (similar to the YAML file)? I think this section could use a bit more info about this.

Installation/Ubuntu-Install-Binary.html

• Regarding the "Installing the missing dependencies" section - If the user wants to use the ROS 1 <-> 2 bridge, does it only work with Noetic? If a reader wanted to use kinetic for example, would it work? If it does work with previous ROS 1 release, I suggest generalizing this section.

Guides/Installation-Troubleshooting.html

• "Out of memory" section - But what if I need the ros1_bridge? Can I download it precompiled, but otherwise build from source if I don't have that amount of RAM?

Guides/Installation-Troubleshooting.html

• "Multiple host interference" section - Multiple instances of what? My application? Multiple instances of the same ROS node? I know the answer, but it would help to be clear to new users. Perhaps a pointer to other docs that explain the background info required.

Concepts/About-Different-Middleware-Vendors.html

• "Multiple RMW implementations" - Other RMWs like Fast-DDS or Connext can be enabled by installing additional packages,..." Isn't Fast-DDS available without installing any additional packages? Perhaps in some installation scenarios it is not available. If so, OK as is.

Glossary.html

• "rclcpp" - "This includes any middleware related APIs as well as the related message generation of C++ data structures..." Does this mean, "This includes any middleware-related APIs and associated messages..."? IMO, "message generation" refers to a process, while "messages" refers to the things that have been generated by that process. Not clear to me which is meant here.