Enhancements to URDF Importer Articulation in Version 2023.1.1 Ensure Consistent Root Link Designation for Improved Simulation Accuracy

Up until version 2023.1.0, the URDF importer assigned the ArticulationRootAPI to the top-level prim of the articulation structure. The root link was then identified by PhysX through an analysis of the kinematic tree. This practice was revised in version 2023.1.1, whereby the ArticulationRootAPI is now directly associated with the actual root link. For example, in version 2023.1.0, when importing a Franka URDF, the ArticulationRootAPI would be placed on /World/Franka, and PhysX might designate an arbitrary link, such as /World/Franka/Link_0, as the root during simulation. In contrast, version 2023.1.1 ensures that the ArticulationRootAPI is consistently located on /World/Franka/Link_0, establishing it as the permanent articulation root for simulations.

This modification is significant for systems with moving bases, in which former versions might not correctly identify the intended base—such as the main body of the moving base—through kinematic tree analysis. As a result of this update, there are implications for the argument values used in any methods or classes that rely on the articulation root path. This includes the Articulation and ArticulationView classes within the omni.isaac.core extension.

Looking ahead, we aim to enhance the flexibility of omni.isaac.core, enabling it to automatically detect the ArticulationRootAPI among the children prims of a robot when the base prim is supplied as an argument.