Document subordinate nodes aka sub-nodes

[christophebedard]

Issue Type

• 🐛 Bug / Problem
• ✏️ Typo / Grammar
• 📖 Outdated Content
• 🚀 Enhancement

Distribution

all

Description

I realized that subordinate nodes are not mentioned anywhere in the docs here. See: #5426.

Affected Pages/Sections

No response

Screenshots or Examples (if applicable)

No response

Suggested Fix

Consider documenting sub-nodes:

1. Explain the concept of sub-nodes in the node concepts page: https://docs.ros.org/en/rolling/Concepts/Basic/About-Nodes.html
   • This might be too advanced for this basic concepts page, though
2. Explain why/in what situations sub-nodes might be useful and show how they're used in a tutorial or how-to guide
   • I think it might make more sense as a tutorial
   • Maybe a "Using sub-nodes" intermediate tutorial, similar to the "Using the Node Interfaces Template Class (C++)" tutorial: https://docs.ros.org/en/rolling/Tutorials/Intermediate/Using-Node-Interfaces-Template-Class.html
3. Find where it would make sense to link to these new concepts/tutorials pages

Additional Context

The best documentation we have right now for sub-nodes is the rclcpp::Node::create_sub_node() documentation: https://docs.ros.org/en/rolling/p/rclcpp/generated/classrclcpp_1_1Node.html#classrclcpp_1_1Node_1a8d5b012d7366795fbc8bb315be13a51b

See the original PR: ros2/rclcpp#581. It's interesting to note that it comes from wanting to add a "NodeHandle"-like concept like ROS 1 had: ros2/rclcpp#531.

[SuperGops7]

Hey @christophebedard I can help with this issue

[fujitatomoya]

@SuperGops7 all yours, thanks!