Jointly glossary

Short, precise answers to the terms that come up when moving a robot from CAD into simulation.

4 pages

• What is URDF?

  URDF (Unified Robot Description Format) is the XML format ROS, Gazebo and MoveIt use to describe a robot's links, joints, inertia and collision geometry.

• What is MJCF?

  MJCF is the native XML format for the MuJoCo physics engine, defining a robot's bodies, joints, actuators, sensors and solver/contact parameters for simulation and RL.

• What is a URDF inertia tensor?

  A URDF inertia tensor is the six-value 3×3 matrix (ixx, ixy, ixz, iyy, iyz, izz) in a link's <inertial> block that tells the simulator how mass is distributed, and how the link resists rotation.

• B-Rep vs mesh: which CAD geometry gives better robot joints?

  STEP/IGES B-Rep geometry stores exact analytic surfaces and their axes, so joint axes can be recovered exactly. A mesh only approximates the surface with triangles, so joint inference is heuristic.