Position and orientation tracking in VR devices

The absolute minimum of information that immersive VR (Virtual Reality) requires, is the position and
orientation of the viewer’s head, needed for the proper rendering of images. Additionally other
parts of body may be tracked e.g., hands – to allow interaction, chest or legs – to allow the
graphical user representation etc. Three-dimensional objects have six degrees of freedom
(DOF): position coordinates (x, y and z offsets) and orientation (yaw, pitch and roll angles for
example). Each tracker must support this data or a subset of it. In general there are
two kinds of trackers: those that deliver absolute data (total position/orientation values) and
those that deliver relative data (i.e. a change of data from the last state).

The most important properties of 6DOF trackers, to be considered for choosing the right
device for the given application are,

  1. update rate – defines how many measurements per second (measured in Hz) are made.
    Higher update rate values support smoother tracking of movements, but require more
    processing.
  2. latency – the amount of time (usually measured in ms) between the user’s real (physical)
    action and the beginning of transmission of the report that represents this action. Lower
    values contribute to better performance.
  3. accuracy – the measure of error in the reported position and orientation. Defined
    generally in absolute values (e.g., in mm for position, or in degrees for orientation).
    Smaller values mean better accuracy.
  4. resolution – smallest change in position and orientation that can be detected by the
    tracker. Measured like accuracy in absolute values. Smaller values mean better
    performance.
  5. range – working volume, within which the tracker can measure position and orientation
    with its specified accuracy and resolution, and the angular coverage of the tracker.Beside these properties, some other aspects cannot be forgotten like the ease of use, size and
    weight etc. of the device. These characteristics will be further used to determine the quality and
    usefulness of different kinds of trackers.
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  1. #1 by Monika Raj on July 27, 2012 - 1:45 pm

    Thanks, The tracking in Virtual Reality & it’s Properties is so good and interesting.

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