Paul Franklin wrote:
On 25 Dec 2005 18:06:18 -0800, wrote:


Are you sure there are ones that measure by laser? Ultrasound ones use
the bounced back wave to figure out the distance. To do this with a
laser would require an extremely fast processor...we're talking
supercomputer.

Mike


Sure, here's a link:

http://www.leica-geosystems.com/cpd/.../lgs_31658.htm

If you read the faq (there's a link on the above page), they go into a
little detail about looking at the phase shift of the returned pulse
train. Using a phase comparison of two pulse trains (emmitted and
returned) avoids having to have a processor fast enough to measure the
round trip time of a single pulse. Rather clever, actually...

That's how GPS works. They match up a 1023 bit random string of bits to
get the high accuracy after a course measurement by more standard
techniques.