Computing the Physical Parameters of Rigid-Body Motion from Video

Abstract

Abstract. This paper presents an optimization framework for estimating the motion and underlying physical parameters of a rigid body in free flight from video. The algorithm takes a video clip of a tumbling rigid body of known shape and generates a physical simulation of the object observed in the video clip. This solution is found by optimizing the simulation parameters to best match the motion observed in the video sequence. These simulation parameters include initial positions and velocities, environment parameters like gravity direction and parameters of the camera. A global objective function computes the sum squared difference between the silhouette of the object in simulation and the silhouette obtained from video at each frame. Applications include creating interesting rigid body animations, tracking complex rigid body motions in video and estimating camera parameters from video.

Binding Computer Vision to Physics Based Simulation: The Case Study of a Bouncing Ball

“…This work is most closely related to the works in [3,15,18]. Metaxas and Terzopoulos [18] defined a continuous Kalman filter that was able to track a deformable object.…”

“…Although interesting, the extensibility of their approach is hindered by this tight coupling. Bhat et al [3] performed 3D tracking of an object by searching over parameterized experiments that optimally project back to an image sequence. However, the shape of the object and the restriction that it is tracked while in flight does not expose the full potential of employing physics.…”

Physically Plausible 3D Scene Tracking: The Single Actor Hypothesis

“…Going further, they incorporated a friction model for a ground that affords human motion upon it [5]. Bhat et al [2] performed 3D tracking of an object by searching over parameterized experiments that optimally projected back to an image sequence. Duff and Wyatt [8] used physical simulation and search heuristics to track a fast moving ball, despite occlusions and for the 2D case.…”

Estimating contact dynamics

“…At a lower level, using modal analysis Pentland and Williams considered the inference of material properties from two non-rigid colliding bodies, assuming that the time-varying shapes of the two bodies are given [13]. Bhat et al [2] estimate physical properties of rigid objects in free flight but do not address the issue of contact.…”