objectrelative

Objectrelative refers to a reference frame or coordinate system that is attached to a specific object. In robotics, computer vision, and augmented reality, quantities are often expressed in the object's local coordinates because this can simplify interaction with the object and make measurements invariant to global motion.

A typical objectrelative frame is defined by an origin and orientation fixed to the object, forming a pose relative to a global or world frame. A point described in object coordinates can be transformed into the world frame using a rigid body transform. If p is a point in object coordinates and T_world_object = [R, t] is the object’s pose in the world frame, then the world coordinates are P_world = R * p + t. Conversely, to express a world point in the object's frame, one applies the inverse transform.

Common uses include robotic manipulation and grasping, where commands are issued in the object’s frame, pose estimation of the object, and alignment tasks in augmented reality or assembly. Objectrelative representations are often implemented with homogeneous transformation matrices (4x4) or with rotation (quaternion or matrix) and translation components, and are integrated into transform trees in systems such as ROS to keep track of multiple frames over time.

Obtaining an objectrelative frame typically involves detecting or registering the object against a known model or markers, estimating its 6-DoF pose, and maintaining consistency across sensor data. Challenges include object symmetry, occlusion, changes in appearance, and differences in frame conventions between systems.

Related concepts include world-relative and camera-relative coordinates, as well as general reference frames and pose representations.