On 26 Apr 2004 09:49:25 -0700, (Eric) wrote:

The police radar guns work off the doppler affect (for radar guns) or
the change in distance between pulses for lidar. My question is how
they account for angle, can a police officer who is at a 87 degree
angle correctly measure your speed?

Look up the 'cosine effect' in relation to traffic radar.

No, he cannot *accurately* measure your speed unless you're directly
in line with him, however errors from radar at an angle are all in
favor of the motorist, so there's no point arguing in court. The
officer's radar gun will read a lower speed than you were going unless
you are traveling straight towards him or straight away.

It should only work going straight at or away from.

Right. But again, errors are in favor of the motorist.

And, frankly, it doesn't matter. The officer's claim and educated
opinion based on experience and training is what matters, especially
in court. The radar is only a tool. A competent police officer can
glance at you driving by and know your speed within a small margin.
The radar just confirms it.

Also, do the police always have their gun on?

Usually not.

Radar is dying in favor of Lidar, esp X band.

A lot of things false trigger radar detectors. Radar can reflect off
overhead signs and over hills where it may trip your detector even
though the radar operator doesn't have a line of sight on you and
couldn't get a reading. Burglar alarm microwave motion detectors and
automatic door openers at supermarkets almost always operate on X band
and will trip radar detectors to a significant distance. Most people
regularly driving a route will learn these areas. These signals always
are present.

There are a very few instances where communities have taken
used/obsolete radar equipment and locked it in transmit to try to slow
down traffic near construction sites, schools or residential areas. An
experienced user of a radar detector will spot these immediately.

Do some Google searching and you'll find a week's worth of reading on
these matters.

Steve


************************************************** *******************
Steve Uhrig, SWS Security, Maryland (USA)
Mfrs of electronic surveillance equip
website http://www.swssec.com
tel +1+410-879-4035, fax +1+410-836-1190
"In God we trust, all others we monitor"
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