PlanSys2 adopts Kairos planner and STN behavior tree builder

The PlanSys2 project is introducing two major updates: Kairos, a new default temporal and numeric PDDL planner, and STNBTBuilder, a new default behavior tree builder. Kairos is a standalone C++ library that outperforms several existing planners in benchmarks, while STNBTBuilder enables better parallelism and required concurrency in robot plans. These changes will arrive in the ROS 2 Rolling distribution first.

Technical improvements in PlanSys2

• Kairos planner: Supports PDDL, PDDL2.1, and PDDL3, including features like negative preconditions, conditional effects, and object fluents.
• Library integration: The plansys2_kairos_plan_solver plugin calls Kairos as a library, avoiding the overhead of launching new processes or writing files for each plan.
• STNBTBuilder: Uses a Simple Temporal Network (STN) to build behavior trees, allowing actions to start based on event dependencies rather than sequential completion.
• Concurrency: Enables plans where one action must occur during another, a capability missing in the previous builder.

Why it matters

These updates enhance the ability of ROS 2-based robots to handle complex, time-sensitive tasks with higher concurrency and more efficient planning logic.