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From: kilian@cray.com (Alan Kilian)
Subject: Re: Laser Range Finding
Message-ID: <1993Feb5.154648.3047@hemlock.cray.com>
Lines: 27
Nntp-Posting-Host: gopher
Organization: Cray Research, Inc.
Date: 5 Feb 93 15:46:48 CST


Alan,
  Your system sounds interesting. Here are my thoughts:

  1) The beam from the laser diode will be narrow. Lets say it is about 10
     degrees. Because of this the power will not drop off as the cube of the
     distance. You need to figure out how it drops off. (Not too tough)
  2) The return pulse will drop off at a different rate depending on just
     what it hits. If it hits a shiny surface it will drop off at the
     same rate as the outgoing pulse. If it hits a perfectly diffuse object
     it will drop off as the cube of the distance.
  3) "Normal" surfaces are a mix of both specular and diffuce reflectors
     so the specular part will probably go off at funny angle and never
     get back to the sensor so you will only get the diffuse part.
  4) Once you know #1 you should be able to get a reasonable correlation
     between returned intensity and distance.

  The only way to know for sure is to build it and try. Sure there are going 
  to be situations when you will get a wrong answer but that's life.

  Please let the group know if it works.

                            -Alan Kilian
-- 
 -Alan Kilian           kilian@cray.com 612.683.5499 (Work) 612.721.3990 (Home)
 "It is a little hard to tell the difference between a machine that doesn't
  work and a machine that doesn't exist." -Martin Walker quoting someone else
