LEO's & Cosine Error

[Orbital75]

I understand the basic principles of the Cosine Error Effect
but since I'm not an Officer and haven't been properly trained in
Radar Speed Enforcement, I have this question.

How does a Leo go about knowing when Cosine Error has occurred?

Does the Leo make an Educated guess that Cosine Error
has happened?

Even if the Radar equipment could factor in Cosine Error,
wouldn't the Leo still have to know the angle?

I'd really like to hear from some of you that can give
a correct answer to this question, Not a guess.

Roy, it would be really nice to hear what you have to
say about this since you trained officers in speed enforcement
and how to use speed enforcement equipment.

** Who knows, this may turn out to be a good Sticky **

[Google Adsense]

[CJR238]

Well if a LEO is at 90 degrees and his radar shows 0 obviously he couldn’t give you a ticket. He can only give you a ticket for what the radar gun says, he cant make something up.
As you know, if you are at a 35% angle from road and he reads 40 and your speed is 55 this works to your advantage because his gun is showing you going slower than what you are and he can only give you a ticket for what the radar gun says.

But keep in mind there are many other ways a LEO can get your speed and give you a ticket.

Cosine error math/explanation:
http://copradar.com/preview/chapt4/ch4d1.html

[TQUILL]

In most instances, the cosine effect is negligible.

[CJR238]

If he’s trying to get you he will, if not he wont. :wink:

He’s not going to pull out his calculator and figure out your speed than go chase you just to sit at a 35 degree angle or over.

How does a Leo go about knowing when Cosine Error has occurred?

Anything passed strait on could have some cosine error.

Does the Leo make an Educated guess that Cosine Error
Has happened?

Anything passed strait on could have some cosine error.

Even if the Radar equipment could factor in Cosine Error,
Wouldn’t the Leo still have to know the angle?

Yes, but even that would be time consuming. Plus the angle is always changing if he’s not shooting strait on.

He can’t make something up, he must use what his radar gun says if that’s what he’s using to get your speed no matter the angle or real speed.

Anyone else have some info?

[MetalFlame]

I know that some radars that we have in Europe,show speed reading
according to Cosine Effect %.

[aradarnut]

A cosine error that occurs in stationary mode will give a reading that is in favor of the targeted motorist (ie: lower than true speed). On the other hand, a cosine error that occurs in moving mode while the radar is calculating patrol speed will give a false high target speed. This happens because a false low patrol speed is subtracted from the closing speed = inflated target speed.

[KnightHawk]

How does a Leo go about knowing when Cosine Error has occurred?

First, he has to have a good visual of the target vehicle at the which his radar is picking up the target speed. He then assesses his position and angle of antenna. He should be able to know by now if there is a cosine effect and not necessarily a cosine error.

For example, LEO clocked you at 15 mph over PSL at a 45 degree angle stationary. He already knows that the actual speed is more than 15 mph over PSL.

In moving mode, as long as the patrol speed is the same as the actual speedometer of the cruiser, target speed is still acceptable based on good visual ID of target vehicle and position of LEO(some cosine effect and not necessarily a cosine error - It will be up to LEO if he want to use the reading or not and gives you a benefit of a doubt).Most of the time in moving mode, their antenna's are angled not greater than 20 degrees and most roads are parallel to each other. You can see this happening on the newer radar units with fastest and strongest windows like the stalker Dual SL. I can't speak for the other radar systems other than the stalker. But i believe, they work the same in theory.

Does the Leo make an Educated guess that Cosine Error
has happened?

Yes. Based on the good visual ID of the target vehicle and LEO's position/angle of antenna.

Even if the Radar equipment could factor in Cosine Error,
wouldn't the Leo still have to know the angle?

Most likely, LEO won't bother to stop you if the unit will show a cosine error.

[Orbital75]

Yes, I understand all the math involved. Just wondering how an officer
determines the error, it any?

Azonehits made some good points from the Leo's point of view.

[Suf Daddy]

If the display says 70 MPH and that's a violation, he'll come after you.

A sharpy MIGHT add a few MPH in his head to determine IF its a "violation", but the reading on the display should be the one used, not this PLUS cosine........its hard to determine of the top of the LEO's head.

Moving mode:

As stated above this is more problematic.
Older units have batching and shadowing issues, that's why the newer Stalkers has the "optional" VSS system to determine "true" patrol speed.

So with that, who gets their older tickets (determined by a "flawed" moving determination) overturned? Bueler?

MPH had a great graph about cosine error. Google search it and you should find one. Nice x / Y axis graph HTH.

-Suf Daddy

[KnightHawk]

Just wondering how an officer
determines the error, it any?

When LEO's approach angle in relation to target vehicle is too large specially in moving. At 60 degrees, the radar unit will only show 50% of the actual speed. Even with this advantage for the motorist, it doesn't mean he cannot issue you a citation when in stationary mode. Check this link below.
http://www.copradar.com/preview/chap...2.html#ceffect