At 11:58 AM 1/20/98 +0100, Bertel Schmitt wrote:
>I'm working on a security application that detects a moving object (usually
>a human  ...) in an outdoor space measuring approx 200 x 500 ft. Output are
>x/y (maybe even z) coordinates, which are fed to a  x/y/z- mount with a
>video camera on it. Mount gets coordinates, aims, zooms in, focuses -
>smile!. Video camera and x/y/z mount are done. All I need is the ranging
>module. Ultrasound is out of the picture because of the distances involved.
>Motion detectors etc. don't work, because I need the exact location of the
>object, not just presence detection.
>
>Any ideas?
>
What are the details of the space?

Is it enclosed by walls on all four sides?

Can equipment/sensors/etc. be mounted anywhere along the perimeter?
How about within the space?

Is the space empty, or are there obstacles that would cause "blind spots"?

What resolution is needed -- how accurately does one need to locate the
target?

Is it possible to mount some sort of device to the target?  (Not likely, as
you mentioned security, but I thought I'd ask...)

In any case, here's a possible solution, assuming the following:
 - Space is normally empty
 - Sensors may be placed along perimeter, but not in center
 - Position of target needs to be accurate within 3 feet or so
 - Position updates needed every few seconds.

Place triggerable xenon flash units behind IR filters every 10 feet along
both long walls.  Place IR sensors every foot or so along both long walls.
Trigger each flash in sequence, recording which sensors do *not* see which
flashes.  Lines drawn between flashes and the sensors "in the dark" will
intersect the target.  Simple algebra calculates intersection point for
each pair of readings.

 - Rick "Impractical Ideas Ya Us" Dickinson

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