An acquaintance of mine is wondering about lidar sweep errors.

This person got a ticket for going 58 in a 45, but on a road where you always know that you should go the speed limit as is the case with all roads. I really think they were going really close to 45, but the lidar said otherwise. 

https://docs.google.com/file/d/0B941PmRjYRpnX3ZqLWlQMGdGXzQ/edit

If you use the formula on page 32 of this Google doc, a sweep error of 6ft would make a 45 mph reading 58 mph. The lidar beam at 1000ft might be 36" so that is maybe about as wide as the bags which are about 6ft back from the headlight. There are no details of which gun was used or at what distance.

Is this just a crazy coincidence?

https://www.youtube.com/watch?v=nm_99S1RoPU

Here is a demo on a parked car. Kustom Signals Pro Laser III LiDAR still looks to be the most  common. It seems like all you would have to do it aim at the motorcycle which would hit the bag and then when you really aim, it would hit the light. That seems like something you could do without knowing it.

The distance from the lights to the bags is closer to 4 1/2 ft. That would make the sweep error closer to 10 mph in this case. The frontal area of the bag is about 7 times greater than a headlight. It seems to me that that given that the beam is so wide, it would be impossible to not have this error be a routine occurrence.  I guess I will add that lidar only measures distances and derives the speed from that.

Of course this is all academic as when it comes to going to court to fight what you think is wrong, the judge will believe the officer over you in most cases.  Doesn't make any difference at all unless the judge gets inundated with people going to court from the same officer on the same day with all of them complaining about the tickets.  Your friend doesn't have a chance in not making the ticket stick.  Been there, done that, got the t-shirt and the ticket.