[aprssig] APRS speed and Cosine Rule?

[Robert Bruninga]

Thanks!

Cosine of 10 degrees is 98.5% so that is very little error.  That means
only about 1 MPH difference at 60 MPH…



Thanks

Bob



*From:* Rusty Bryant <rustyb78 at yahoo.com>
*Sent:* Tuesday, June 9, 2020 11:15 AM
*To:* aprssig <aprssig at lists.tapr.org>; Robert Bruninga <bruninga at usna.edu>
*Cc:* wb4apr at aprs.org
*Subject:* Re: [aprssig] APRS speed and Cosine Rule?



Bob,

If you want me to keep you safe I'll say YES, but the reality is, most
radar units in police cars do not use a cosine rule.

Part of our training is that we should keep a 10 degree or less angle
between our unit and the target.

But, any increase in angle will only benefit the suspect.  If they are
going 30 mph over the speed limit and our radar indicates that you are only
going 20mph over the limit, then you just got away with the 10mpg delta.

Just remember this, when you double your speed, you quadruple the impact
force if you crash.

Speed Kills!

Rusty
WB4BSD





On Monday, June 8, 2020, 4:07:49 PM EDT, Robert Bruninga <bruninga at usna.edu>
wrote:





APRS speed related?



Have cop radars implemented the Cosine rule?  IE, it should be possible to

include a magnetic compass in a handheld radar gun and to initialize it in

the direction perpendicular to the road with just a button push...



Then the gun can display the actual speed using the cosine rule as the cop

sweeps to keep up with your car, (or statically when the cop is at an

angle to the line of approach) and not just the relative speed (which

approaches zero) as the car goes past the perpendicular point.



Curious as to whether I need to consider this when speeding past a

radar...



Bob, WB4APR



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