From ascen@world.std.com Wed Jun 7 09:45:34 1995 Date: Tue, 6 Jun 1995 17:13:28 GMT From: Ascension Technology Newsgroups: sci.virtual-worlds Subject: Re: TECH: Tracking Person's Movement Christian Soldier (christian@gatecoms.gatecom.com) wrote: : I was wondering how current VR systems track a person's movement, i.e. : direction facing, head tilt, and position? Does it employ : phase-variance radio readings, tilt indicators, etc? Also, how is this : movement translated into a digital signal? : I am looking for information and sources. *Ascension Flock of Birds* The Flock of Birds(TM) motion capture system from Ascension uses pulsed DC magnetic fields generated from 3 orthogonal coils. Each square-wave pulse is measured by 3 orthogonal coils (centered around a flux-gate). The 9 measurements (and 3 background) are combined to determine a unique 6 degree of freedom (x, y, z, and Az, El, Roll for example) solution. Receiver and transmitter connect to an electronics unit. Communication to host computer can be through RS232 or RS485. Advantage: Low sensitivity to eddy-current distortion in electrically conductive materials, such as metal. For some more technical detail, download binary file tecpaper.ps from ftp.std.com /ftp/vendors/Ascension. Also, feel free to download our user software which contains source code for interfacing to our Flock systems. * AC based trackers * Another type of magnetic based tracker uses AC fields, transmitted by 3 orthogonal coils. The 3 AC signals are continuous and out-of phase from each of the transmitter coils. The receivers are 3 orthogonal coils. No background measurement is needed, because the receivers only measure *changing* magnetic fields. Some AC based systems are contained in a separate electronic unit, or on a PC card, such as the Ascension SpacePad. * Other tracking systems * Video based; Video tracking of 'dots' placed on person. Multiple cameras are used for 3D. Physical tracking; The object or person is attached to a flexible arrangement, and movement is measured on potentiomaters. Acceleromiters; Changes is position requires acceleration (2nd derivative), these changes are measured and integrated. Gyroscopic; measures 3 degree of freedom. Sound based; Speed of sound is known. Transmitter broudcasts, and timing is used to determine distance. Transmitters (usually 3) are used. Finger tracking generally uses fiber optics (light characteristics change when cable is stressed) Did I leave out any? Hope this helps. Regards, Steve Work