# Thread: Important lidar question (incorrect targeting angles)

1. ## Important lidar question (incorrect targeting angles)

Here it goes.

The other day I was driving on my normal route. Being the paranoid driver that I am, I always keep an eye out way up ahead for parked cars or motorcycles (for obvious reasons). Well this time, my vigilance paid off as I saw a cruiser parked perpendicular to the road from around 3/4 of a mile away. It was a CHP.

I checked my speed and passed him. He was shooting lidar so I kept coming back and forth trying to get him to shoot me but he didn't (or at least the V1 never alerted so I doubt he shot me).

The strange thing: He must have been shooting the lidar at a 10 degree angle or so. He was parked on one side of the street and then shooting traffic approaching him in the other lane. Keep in mind, he must have been about 20 feet off the road already (or more).

WOULDN'T THIS INTRODUCE ERRORS? I THOUGHt THE LINE OF SIGHT NEEDS TO BE RELATIVELY STRAIGHT FOR LIDAR TARGETING?

If you imagine a right triangle, the distance (being the short leg) measuring from his point to the other lane must have been atleast 35 feet or more.

Any Ideas? Possibility of error?

By the way, when I passed him the last time he pulled out after me to head home. He flipped on his stalker (instant on mode) and the V1 lit up like a Christmas tree. Why in the hell would someone be stupid enough to speed anyway when they see him pull out? Hmm, I guess some would be stupid enough though.

By the way, I think most of the CHP are still amateurs in my area with lidar (whether officially certified or not) so It wouldn't surprise me if they lacked knowing the proper techniques for lidar targeting. It you would have seen this situation, I think you would have been equally concerned over the very wide angle.

2. The angle between the target vehicle and radar/laser usually has to be more than about 30 degrees before the error amounts to more than 1-2 mph, provided that the target is more than about 200' away. 10 degrees isn't significant enough and is probably realistic for an officer that is parked to the side of the road.

3. Originally Posted by bart99gt
The angle between the target vehicle and radar/laser usually has to be more than about 30 degrees before the error amounts to more than 1-2 mph, provided that the target is more than about 200' away. 10 degrees isn't significant enough and is probably realistic for an officer that is parked to the side of the road.
X2, Im sure laser has the same off axis Cosine error/effect problems as radar.

4. I've been shot off axis but in this case it was a moto unit scrambling to get a reading because I assume he didn't see me until I was too close. ZR3 got a piece of it but I doubt he was registering much of a speed at that tight of an angle. Definitely less than 30 degrees.

YouTube - Houston PD Off Axis laser hit on my ZR3

5. The farther away the target the farther away from the the road the officer can be, (why am I hearing YODA in my head). Trigonomitry shows this with Pythagrian therom.

6. Well, LIDAR does suffer from the same effects as radar at nearly the same rate of DECLINE. Just like radar, cosine in LIDAR works in your favor. So if he wants to sit that far off the road, yes there will be an error, but it will be a lower speed reading, he may or may not know this, but it can only be good for you depending on your speed, and his angle, he might not pull you over.

7. The error works out in your favor, and the farther away he targets the less the error will impact his reading. Cops have to make a trade off between their safety and greed for giving out tickets, and I hope they choose the former.

8. Thanks so far.

The reason I posted this is because it looked really strange. Normally they target a lane from the same side of the road (from what I have seen anyway).

This has been true even for radar .

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