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[David C Nickerson]

Hoping someone can help me crunch this...

If I'm holding a LIDAR laser gun, and have a target at 584', how much does my beam move, if I'm handheld with my gun, assuming I move 1/8", 1/4, maybe 1/2"?

I've figured there's a 21" beamwidth at range, but am thinking that a little wiggle in the trooper's hand could have had him shooting the footbridge, and not me.

Hoping to raise enough doubt to save $3K in insurance penalties.

Thanks in advance,
David

[Chris Davis]

It's late and past my bedtime, and the SOH CAH TOA gods were already asleep.  So here is a quick and dirty ratio method of approximating it since no angles were given or used.  

I guessed that the end of the handgun is probably about 6" away from the pivot of the wrist, although the 6" is just a speculative number and a more accurate number could be substituted here if known.

Then 1/8", 1/4", and 1/2" would be the distance traveled at 6" (at the end of the gun...this is what you were thinking, right?).

Then I solved for the distances traveled at 584', except that I solved for it in terms of inches, then converted the answers to feet.  The first one would be (7008" * .125") / 6" = 146"



P.S.  None of this accounts for your estimated 21" beamwidth at 584'

[Andy Zimmerman]

David C Nickerson wrote on Tue, 21 December 2010 23:31

Hoping someone can help me crunch this... If I'm holding a LIDAR laser gun, and have a target at 584', how much does my beam move, if I'm handheld with my gun, assuming I move 1/8", 1/4, maybe 1/2"? I've figured there's a 21" beamwidth at range, but am thinking that a little wiggle in the trooper's hand could have had him shooting the footbridge, and not me. Hoping to raise enough doubt to save $3K in insurance penalties. Thanks in advance, David

Just how fast was this footbridge going?

According to wiki, these devices obtain their reading within a fraction of a second. How much wiggle is going to occur in that time frame?

http://www.sunley.ca/lidar.htm

http://en.wikipedia.org/wiki/LIDAR

http://tipmra.com/

Good luck. I think that you are going to need it.

PS

Couple of recent cases

http://caselaw.findlaw.com/il-court-of-appeals/1482413.html

http://www.state.hi.us/jud/opinions/ica/2006/ica26272.htm

[Matt Vivlamore]

After sitting in court a couple times...
I’ve seen a few people argue that the officer pulled over the wrong car, and that other car was passing them and so they weren’t speeding.
Apparently the laser guns have a set of crosshairs they look through and the officer can see the "dot" on your car while reading your speed.



*Yes, I go to court after being pulled over.  In MD, depending on your driving record and issued ticket, you can trade in your fines and/or points for Volunteer work.  

[Charlie Zureki]

 Hello,

  I'm guessing you're going to Court to argue that this Patrolman could have been actually measuring something else besides your vehicle?

  Good luck, hopefully the Court will indulge you...but, I hope that you're prepared to actually show through a model or physical demonstration.

  If it's a Lidar, then, take (with permission of the Court) a  laser pen and a couple of mirrors for an incidence/reflection demonstration. (he could have been measuring something else)

  Ask when the gun had been last calibrated prior to the event, to what "standard" , and who calibrated it and were they certified to actually calibrate it?  Do they keep records of these calibrations?

  Find the model number of the gun the patrolman used and get the specs. It could have a +/- in your range example that makes the patrolman's claim questionable.
   
 In a proper Court, you'd only need to show a doubt that the measurement was correct.

 Good Luck,

 Hammer

[Dan Johnson]

Chris Davis wrote on Wed, 22 December 2010 01:28

I agree with Chris' numbers.  And I assume this gives you more than enough info to factor in your 21" beamwidth and still have the margin of error you were hoping for. There would be the same margin of error in the horizontal plane as well as the vertical plane of course. I would think the much harder thing about this would be to prove that the cop was where you say he was and that you were where you say you were when he took the reading. As others have said though, there are other factors that support the officer's aim being reasonably accurate.  And how do you explain the footbridge moving at that speed?

[John Roberts {JR}]

You need to know the angle of error? Which will be harder to explain in court since few people have a grasp of how much 2' or 20' is.

While the traffic court judge may have heard of "cosine error" http://copradar.com/preview/chapt2/ch2d1.html

The bad news is, that cosine error causes the device to under report speed, when measured at an angle so don't bother with that, but the geometry is similar.

You have a slender chance if you were in traffic and being passed by somebody, and the officer doesn't show up. You weren't likely to be passed by a moving bridge.  

The devices typically lock on the fastest/strong ping return, they probably try to filter out returns that don't show movement.

JR

[Bennett Prescott]

Charlie Zureki wrote on Wed, 22 December 2010 09:24

Ask when the gun had been last calibrated prior to the event, to what "standard" , and who calibrated it and were they certified to actually calibrate it?  Do they keep records of these calibrations?

This is how you win this. You are not going to convince a judge that a footbridge was going 90MPH. Try asking to see the gun's source code, after all, you hbe a right to face your accuser.

In the past I have gotten the DA talked down to a two point non-moving violation with little effort. The one time I hired an attorney I got that same deal.

[Stavross (Sam Buck)]

Ask for an extension, this should move the court date back between a couple weeks and a month. Repeat at least one more time. Trooper doesn't show up, you win.

[Dave Bigelow]

Stavross (Sam Buck) wrote on Wed, 22 December 2010 10:47

Ask for an extension, this should move the court date back between a couple weeks and a month. Repeat at least one more time. Trooper doesn't show up, you win.

Exactly, that is what most lawyers are gonna do anyway.



I don't see why you are going through all of this for a speeding ticket when using the good old mechanical failure defense works almost every time.