SOund NAvigation Ranging, or sonar, is more or less the same thing as
ultrasound, except that it implies the transmission medium is water. I
doubt your car is ocean worthy.
RF is worthless as a parking aid as various things which you don't want to
run your car into are transparent to it, aside from the fact that it
propagates at the speed of light and is therefore useless for measuring very
short distances with.
Most things aren't transparent to infrared light, but given that they
reflect different levels of it, it can't readily be used for measuring
absolute distance with, at least not without knowing how reflective the
object is ahead of time. I suppose some exceptionally smart software and
optics could determine a distance for you, though, given that digital
cameras can automatically focus themselves.
Ultrasound is a tried and proven technology which stikes me as the most
logical technology to use. You might wish to take a look at "Good old'
parking sonar [
http://www.geocities.com/CapeCanaveral/Launchpad/3632/sonar.htm ]. It seems
as others misuse the terminology too.
Howard Heny Schlunder
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