OPTICAL TRACKING

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OPTICAL TRACKING

• Mithat Daglar
  
  
  Ltjg.

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Presentation Outline

• Overview
• How they work
• Advantages
• Disadvantages
• Eye Tracking
• Links

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Overview

• The mostly used trackers use magnetic field. The
  biggest problem with the magnetic trackers is
  their limited range. As the range increases so
  the possibility of distortion is also increases.
  They are also very too much sensitive to the
  environment. Metals and electromagnetic
  interference cause distortion in the result.
• The optical trackers are used to overcome these
  limitations.

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Overview

• Optical trackers are mainly used for two
  purposes in computer applications
• For computer animation (human movement analysis)
• Virtual environment (to capture the precise
  information about the position and the
  orientation of the users head)
• Early examples of optical trackers, such as
  Op-Eye and SelSpot were used by MIT and New York
  Institute of Technology in 1982-1983.

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How They Work

• Optical tracker systems use either reflective or
  IR-emitting markers and video cameras to monitor
  the tracking space.
• For body motion analyze 20 - 30 markers are
  attached to the body (especially to the joints).
  Number of the markers depends on the the desired
  resolution. More markers give more accurate
  results.
• The markers are small spheres or disks covered in
  reflective material. Can be distinguished by
  their shape, brightness and size.

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How They Work
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How They Work
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How They Work
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How They Work

• The markers are imaged by high speed digital
  cameras. The number of the cameras depends on
  the type of motion capture.
• Facial motion capture usually uses one or two
  cameras. Full body motion capture may use four
  to six cameras to provide full coverage of the
  active area.
• To enhance contrast, each camera is equipped
  with IR-emitting LED

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How They Work

• IR pass filters are placed over the camera
  lenses.
• Cameras are attached to the controller cards,
  typically in a PC chassis.
• Before motion capture begins, a calibration
  frame -a carefully measured 3D array of markers-
  is recorded. This defines the frame of reference
  for the motion capture session

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How They Work

• During the motion capture session, the computer
  is presented with each camera view.
• After the motion capture session, the recorded
  2D motion data is converted to 3D position data
  by using triangulation approach.
• This resultant data is typically applied to an
  inverse kinematics system, to animate a skeleton.
  

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How They Work

• Actions
• Chutes
• Courses
• Face
• Expressions
• Combats
• Sports
• Extra

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How They Work (wide area tracking)

• In a virtual environment, to provide the user
  with the impression of being immerse in the
  simulated 3D environment, precise information
  about the user s head is required.
• For this purpose, another optical tracking system
  is used and is called Wide Area Tracking.
• This system uses ceiling panels housing LEDs, a
  miniature camera cluster called HiBall and a
  single-constraint-at-a-time (SCAAT) algorithm
  which converts individual LED position into
  position and orientation data.

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How They Work (wide area tracking)

• Ceiling
• Current applications cover up to 4,000 cubic
  feet.(500 sequare feet X 8 feet). But can be
  easily expanded by adding new tiles.

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How They Work (wide area tracking)

• HiBall

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How They Work (wide area tracking)

• HiBall is a cluster of 6 lenses and 6
  photo diodes
  arranged so that each
  photo diode can view LEDs
  thorough
  several lenses.
• SCATT algorithm computes the position
  of the user by using
  the LED sightings
  provided by HiBall.

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Advantages (Optical Body Motion Tracking)

• Large Possible Active Area Unlike magnetic
  tracking system, depending on the system used and
  the precision required, the motion capture area
  can be arbitrarily large.
• Unencumbered Subject The subject is not
  physically attached to the tracking system.
• Markers are passive Since markers are the
  active elements of the system, additional markers
  cost very little. Hundreds of markers can be
  used for a motion track.

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Advantages (Optical Body Motion Tracking)

• High enough sampling rate for most sport moves
  At 120 to 200 Hz sampling rate, most human
  motions are easily measured.
• Free from electromagnetic interference.

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Disadvantages (Optical Body Motion Tracking)

• Cost Most expensive tracking systems.
• Bioengineering Technology Systems (Superfluo)
  Uses passive markers. 135,600 (50Hz) 33,000
  (for upgrade to100Hz)
• Selspot AB(Selspot II) IR LEDs - 37,000
• Northern Digital (Optorack) IR LEDs - 80,000
• Motion Analysis Corp (Expert Vision 3D) 38,
  500

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Disadvantages (Optical Body Motion Tracking)

• Sensitivity to light Background, clothing,
  ambient illumination effect the accuracy.
• Sensitivity to reflection Wet or shiny
  surfaces (mirrors, floors, jewelry, and so on)
  can cause false marker readings.
• Marker Occlusion Since a marker must be seen
  by at least two cameras (for 3D data), the
  occlusion caused by subject (human), materials
  in the environment and the other markers can
  result in lost, noisy, displaced or swapped
  markers.

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Disadvantages (Optical Body Motion Tracking)

• Tracking time Tracking time can be much greater
  than the actual capture session and may vary
  unpredictably, depending on accuracy
  requirements, motion difficulty, and the quality
  of the raw data captured.
• Non real-time device Since there is no
  immediate feedback , it is impossible to know if
  a motion is adequately captured. More than two
  sessions may be needed.
• Sensitivity to calibration Since multiple
  cameras, the frame of reference for each camera
  must be accurately measured.

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Eye Tracking

• Are similar to optical trackers. Using infrared
  illumination and lightweight high-resolution
  video sensors.
• The IR waves created by IR LEDs are reflected by
  the eye. This reflection is captured by video
  sensors and white and black colors are used to
  calculate the position of the pupil.

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Eye Tracking(SensoMotoric Instruments products)

• Headband/Helmet-mounted Eye tracking Device
• Can record eye movement with unrestricted head
  movement

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Eye Tracking(SensoMotoric Instruments products)

• Remote Eye tracking Device (R.E.D.)
• Eye movements can be acquired without physical
  contact to the subject.
• The R.E.D., placed in front of the subject
  below the line of sight, automatically tracks
  the subject¹s eye within the range of natural
  head movements.

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Eye Tracking(SensoMotoric Instruments products)

• Head Mounted Display with integrated eye
  tracking (H.M.D.)
• Integrated with Head-mounted display (HDM).
  Useful for virtual reality applications.

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Eye Tracking(Quick Glance)

• Consists of two IR LEDs and a camera
• The camera and light sources are
  mounted on the
  computer's monitor.
• Examines the reflections from the user's eye
  which is illuminated by LEDs . The reflected
  light is focused onto the camera. By analyzing
  the position of the light reflections and the
  center of the pupil contained in the image, the
  gaze point is determined. Duration can also be
  derived. With that information, the software
  controls the location of the cursor according to
  the gaze point and its duration.

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Eye Tracking(ISCAN)
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Links

• Optical Tracking
• http//www.cs.unc.edu/tracker
• http//www.ndigital.com
• http//www.peakperform.com
• http//www.motionanaliysis.com
• http//www.actisystem.fr
• Eye Tracking
• http//www.smi.de/iv/index.html
• http//www.gkc.co.uk/vr-systems/borgtext.htm
• http//www.dinf.org