Optimizing Latency vs' Throughput in a Collaboratively Controlled Webcam System

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Optimizing Latency vs. Throughput in a
Collaboratively Controlled Webcam System

• Kaustav Ghoshal
• Dept. of Computer Science
• Texas AM University

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Agenda

• Introduction to the Problem
• The Related Works
• The Problem Definition
• Salient Assumptions
• Complexity in case of a Single Camera
• The Multiple Camera Approach
• Algorithms Used
• Future Enhancements

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Introduction to the Problem

• Original Photo http//students.cs.tamu.edu/kausta
  v/nwrobots/panorama.jpg

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The Related Works

• Flyspec Liu, Kimber, et al
• p center problem
• ShareCam Song,Goldberg

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The Problem Definition

• Conventions
• Pan Angle a
• Tilt Angle ß
• Zoom Level n
• Tuple is thus specified by (a, ß, n)

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Salient Assumptions

• Tilt aspect of the camera is not considered.
• All users given the same priority

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Complexity in case of a Single Camera

• Problem is NP Complete.

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New Complications

• Can the problem be solved in polynomial time?
• How many cameras are required for this?
• What is the minimum number of cameras needed?

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The Multiple Camera Approach

• Use 2 cameras to cover the same pan range.
• Idea of Preemptive Multiprocessor Scheduling by
  Muntz Coffman

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The Multiple Camera Approach

• Let panorama to be covered be ?
• Pan range of each camera be - a to a
• Therefore the number of cameras needed are ?/a
  
• Thus problem can be solved in polynomial time.

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Algorithms Used

• New request scheduled on the following parameter
• f(xi)?(xi)d(i)
• Where
• f(xi) time taken for camera i to orient to the
  position of request x
• ?(xi) time taken for camera i to process
  request x
• d(i) delay at camera i

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Algorithms Used

• Calculation of the function f(xi)
• ?aßdø / f(ø) ?aßdø / f(ø) f (z)
• Where f(ø) and f(ø) are the angular pan and tilt
  velocities
• f (z) denotes the time required for the zoom
  level change

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Algorithms Used

• Multidimensional Divide and Conquer Bentley
• Problem has a running time of O?N lg2N?
• Metric function can be defined as
• n vs. l vs. ?
• Where n -gtnumber of cameras
• l -gt the number of active users
• ? -gt the latency time

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Future Enhancements

• Reduced Rotation Speed of Webcams
• Placement of Cameras in the 3D Space
• Optimization of Algorithms to reduce the lower
  bound ?(N lg N)

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References

• R. R. Muntz , E. G. Coffman, Jr., Preemptive
  Scheduling of Real-Time Tasks on Multiprocessor
  Systems, Journal of the ACM (JACM), v.17 n.2,
  p.324-338, April 1970
• Bentley, J.L., and Shamos, M.I. Divide and
  conquer in multidimensional space. In Proc. ACM
  Symp. Theory of Comptng., May 1976, pp. 220-230.
• M . Bianchi, AutoAuditorium a fully automatic,
  multicamera system to televise auditorium
  presentations, Proc. Of Joint DARPA/NIST Smart
  Spaces Technology Workshop, July 1998
• J. Foote and D. Kimber, FlyCam Practical
  Panoramic Video, Proceedings of IEEE
  International Conference on Multimedia and Expo,
  vol. III, pp. 1419-1422, 2000.
• Q. Liu, Y. Rui, A. Gupta, J. Cadiz. "Automating
  Camera Management in a Lecture Room", Proceedings
  of ACM CHI2001, vol. 3, pp. 442 449, Seattle,
  Washington, USA, March 31 - April 5, 2001.

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References

• D. Song, A. F. van der Stappen, and K. Goldberg.
  Exact and distributed algorithms for
  collaborative camera control. In The Workshop on
  Algorithmic Foundations of Robotics, December,
  Dec. 2002.
• Q. Liu, D. Kimber, L. Wilcox, M. Cooper, J.
  Foote, and J. Boreczky. Managing a camera system
  to serve different video requests. In
  Proceedings of IEEE International Conference on
  Multimedia and Expo (ICME), Lausanne,
  Switzerland, volume 2, pages 1316, Aug. 2002.
• D. Song and K. Goldberg. Sharecam part I
  Interface, system architecture, and
  implementation of a collaboratively controlled
  robotic webcam. In IEEE/RSJ International
  Conference on Intelligent Robots (IROS), Nov.
  2003.
• Q. Liu, D. Kimber, J. Foote, L. Wilcox, and J.
  Boreczky, "FLYSPEC A Multi-User Video Camera
  System with Hybrid Human and Automatic Control,"
  Proceedings of ACM Multimedia 2001, pp. 484 --
  492, Juan-les-Pins, France.

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Doubts, Dilemmas, Concerns Queries !