nivek@rover.ri.cmu.edu (Kevin Dowling) (11/04/88)
There are a number of techniques for measuring distance with lasers, interferometer techniques are common in the laboratory as well as for very accurate longer distance measurements. Interference between a beam and the reflected beam from a target results in fringes that can be seen and counted with simple photodiode set-ups. Accuracy in the the micro-inch range. We have a couple of laser scanners a CMU for robot navigation and they use a modulated beam to measure distance over a wide range fairly accurately. The outgoing beam is modulated by a carrier frequency, and the phase shift between that and the return signal is proportional to distance. A fast clock gives the phase shift between outgoing and incoming signals. Additionally the amplitude of the incoming signal can be used to give reflectance. In our set the laser scanner information is sent to a frame buffer where the brightness on the screen corresponds to distance. Looks neat cause close objects are dark and objects farther away get lighter and lighter. This mapping of distance to gray level plus the reflectance image results in a 'camera' style view plus depth information at every point. (2 axis raster style scanner) As the distance increases the phase shift will become complete (one full wavelength) and this distance is called the 'ambiguity interval' This can be changed or detected in software. Surveying instruments use laser ranging techniques too. The beam is pointed at a corner cube held by an assistant and the beam is reflected back to a detector in the unit. I'm not sure what technique they are using for this but I suspect a phase shift method is used. nivek Aka : Kevin Dowling Bell: (412) 268-8830 Arpa: nivek@rover.ri.cmu.edu Mail: Robotics Institute Carnegie Mellon University Pgh, PA 15213-3890
henry@utzoo.uucp (Henry Spencer) (11/06/88)
In article <3482@pt.cs.cmu.edu> nivek@rover.ri.cmu.edu (Kevin Dowling) writes: >... In our set the laser scanner information is >sent to a frame buffer where the brightness on the screen corresponds >to distance. Looks neat cause close objects are dark and objects farther >away get lighter and lighter... Have you tried inverting the brightness scale? Just curious -- I'd have expected it to look better (to humans, of course) that way. -- The Earth is our mother. | Henry Spencer at U of Toronto Zoology Our nine months are up. |uunet!attcan!utzoo!henry henry@zoo.toronto.edu