ShareCam part II: approximate and distributed algorithms for a collaboratively controlled robotic Webcam

ShareCam is a robotic pan, tilt, and zoom web-based camera controlled by simultaneous frame requests from online users. A companion paper describes the system. This paper, Part II, focuses on algorithms. The ShareCam problem is to find a camera frame that optimizes a measure of total user satisfaction. We present a grid-based approximation algorithm: given camera frame requests from n users, and approximation bound 2, we analyze the tradeoff between solution quality and processing speed and prove that the algorithm runs in O(n/2) time. The algorithm can be distributed to run in O(1/2) time at each client and in O(n + 1/2) time at the server. Experiments suggest that performance of the distributed algorithm degrades gracefully as clients fail to complete their part of the computation. ShareCam can be found online at: http://www.tele-actor.net/sharecam/.