Radar setup angles

[dhunt]

A question for the cops on here. We've been studying a bit about radars lately and was looking at how the angle in which the radar beam is directed must be taken into account to accurately determine speed. What we were discussing is what happens as the angle increases the determined speed will drop. Do you guys taken anything like this into account?


<PRE>
-------------------------------
Road / *vehicle1
/
*cop / ______________*vehicle2
--------------------------------

</PRE>
If vehicle1 and 2 are traveling at the same speed if the angle isn't taken into consideration then vehicle1 will seem to be travelling slower to vehicle 2.

If none of this makes seens to anyone just ignore me. I'm just bored at work. :whocares:

[Hoon]

I wouldn't think so. It works to the drivers benefit anyway as their indicated speed would be lower than their actual speed as the angle increases (Vi = V * Cos Ø).

[spudchucka]

Any angle works in the favour of the targeted vehicle. If there is multiple lanes of traffic then you need to visually confirm which is the fast vehicle. Laser can be aimed at a specific vehicle so you don't have to deal with that issue.

[dhunt]

I wouldn't think so. It works to the drivers benefit anyway as their indicated speed would be lower than their actual speed as the angle increases (Vi = V * Cos Ø).
Yeah that's what I figured.

[marty]

hoon is right. cosine angle is always advantageous to the vehcile being tracked.

[Lou Girardin]

Not quite, cosine error works to the advantage of the target vehicle when it is closing the angle to the patrol car, eg the patrol car is travelling straight and tracking a target approaching on a curve. The opposite is the case when the patrol car is on a curve with the target vehicle approaching in a straight line. Then the radar over-reads.
Don't believe what they tell you at training college boys. One of your bosses, John Kelly, doesn't even know what frequency Stalkers operate on.

[spudchucka]

One of your bosses, John Kelly, doesn't even know what frequency Stalkers operate on.
Why the hell should he? Its not like he goes out and uses the bloody thing! What difference could it possibly make?

[marty]

Not quite, cosine error works to the advantage of the target vehicle when it is closing the angle to the patrol car, eg the patrol car is travelling straight and tracking a target approaching on a curve. The opposite is the case when the patrol car is on a curve with the target vehicle approaching in a straight line. Then the radar over-reads.
.
isn't that what i said?

get a couple of matchbox cars out lou, and do the math in visual symphony, as obviously your tiny brain can't compute it without external input. if the vehicle being tracked (that's you) is travelling at an angle to the vehicle doing the tracking (that's the police - they're the ones in the patrol cars - can you say patrol?), then the cosine angle is advantageous to the vehicle being tracked. there is no circumstance when the radar will read HIGHER due to the angle, regardless if the patrol car is on a corner or on a straight.

[StoneChucker]

What happens if you're on a bike, and doing a wheelie? IF you pinged under the bike, depending on the angle of your wheelie, it would read differently right? SO... If I get pinged doing a wheelie, should I accelerate to decrease the angle (lift bike higher) or touch the rear brake to increase the angle (lower bike). Note angle I mean is angle between laser and bottom of bike, so no angle would be doing a verticle wheelie.

So, which is best, so I know for the future?







hehehehehehe :killingme

[spudchucka]

I think you should just stand up, lift one leg in the air and wave as you zoom past.

[marty]

i'd certainly wave.

[Blakamin]

What happens if you're on a bike, and doing a wheelie? IF you pinged under the bike, depending on the angle of your wheelie, it would read differently right? SO... If I get pinged doing a wheelie, should I accelerate to decrease the angle (lift bike higher) or touch the rear brake to increase the angle (lower bike). Note angle I mean is angle between laser and bottom of bike, so no angle would be doing a verticle wheelie.

So, which is best, so I know for the future?







hehehehehehe :killingme

which is better??? laying it in a gutter ??
:Pokey:

[StoneChucker]

I think you should just stand up, lift one leg in the air and wave as you zoom past.
If I waved, would ya chase me? :msn-wink: :msn-wink: :msn-wink: :lol:

[spudchucka]

If I waved, would ya chase me? :msn-wink: :msn-wink: :msn-wink: :lol:
The only bikers I've ever chased are the types that stink real bad and wear patches on their backs. I've heard it heaps of times over the radio where a cop calls up to say that he just clocked a bike at 240'ish. Ask for a description....."I think it was a red one"! Roger, we'll keep an eye out for a red bike.

If you went past me like that I'd be saying, "There aint no way I'm going to catch that guy so I might as well enjoy the show".

[scumdog]

The only bikers I've ever chased are the types that stink real bad and wear patches on their backs. I've heard it heaps of times over the radio where a cop calls up to say that he just clocked a bike at 240'ish. Ask for a description....."I think it was a red one"! Roger, we'll keep an eye out for a red bike.

If you went past me like that I'd be saying, "There aint no way I'm going to catch that guy so I might as well enjoy the show".
My sentiments exactly s.c.!!!!

BTW Lou, I'm still waiting for a scientific refuting of the argument on how the radar gives a lower reading for a target vehicle approaching a patrol vehicle on an angle than it's actual speed really is.

p.s. , Got 18% in School Cert maths so I shouldn't be too hard to fool!!

[StoneChucker]

Just incase you thought I was serious, I can't even wheelie! :stupid:
But I can understand what you're saying. I heard somewhere (so it MUST be true ;) ) that police have to give up the chase at like 130/140km/h? And if someone flies past you at anything faster than that, you're not going to catch him period. BUT... You have little boxes in your car don't ya, like talking boxes linked to other cars? Sheesh, it's to hi-tech for me :bleh: , but you can't outrun the radio as everyone says...

PS: At those speeds you MAY just catch up to him(*edit* or her*), wrapped around a pole :Pokey:

[thehollowmen]

I'm searching around
Sciam had a nice article about radars and angles... how the radar worked..

Though from memory you're right, it does work to the approaching car's advantage to be at an angle...

edit - this article
http://www.sciamdigital.com/browse.cfm?sequencenameCHAR=item2&methodnameCHAR=resource_getitembrowse&interfacenameCHAR=browse.cfm&ISSUEID_CHAR=FF34F144-FEE8-4F66-ABCB-60DC58A1375&ARTICLEID_CHAR=CD618D0B-05C7-42E3-8F18-AE6A3104B39&sc=I100322

sure I've got it in a mag ... I'll scan if you want

[thehollowmen]

right... looked through the shelf and that one is missing
but I did find this website:
http://copradar.com/preview/chapt1/ch1d1.html

"The angle between the (microwave or laser) radar and target (alpha in the figure below) must be small for the radar to accurately measure speed. The angle is referred to as the Cosine Effect angle because measured speed is directly proportional to the cosine of this angle; the larger the angle the lower the measured speed"

I think this means if you're 10 lanes over and at a close to 90 degrees from the cop you will be pretty much safe :-P

they have lots of neat chapters on this... the 'cosign defence' and other things:
http://copradar.com/preview/chapt7/ch7d2.html#ceffect
http://copradar.com/preview/chapt4/ch4d1.html

hope this clears up a few questions

[scumdog]

right... looked through the shelf and that one is missing
but I did find this website:
http://copradar.com/preview/chapt1/ch1d1.html

"The angle between the (microwave or laser) radar and target (alpha in the figure below) must be small for the radar to accurately measure speed. The angle is referred to as the Cosine Effect angle because measured speed is directly proportional to the cosine of this angle; the larger the angle the lower the measured speed"

I think this means if you're 10 lanes over and at a close to 90 degrees from the cop you will be pretty much safe :-P

they have lots of neat chapters on this... the 'cosign defence' and other things:
http://copradar.com/preview/chapt7/ch7d2.html#ceffect
http://copradar.com/preview/chapt4/ch4d1.html

hope this clears up a few questions

AND if you're not exceeding the speed limit you are even safer!! :2thumbsup

[TwoSeven]

From my understanding of radar, I dont think there are any angles involved. Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.

[thehollowmen]

From my understanding of radar, I dont think there are any angles involved. Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.

yes, but this is saying the radar measures the speed of the object directally in frount of it as though it was moving directally towards the radar... it can't measure side to side movement unless it has some form of reference object...

If I walk towards you at a pace every second, you'll see me walk at a pace per second towards you...

now if I walk at 45 degrees to that... at a pace per second... it will look like I'm moving slower directally towards you (about 70% of the speed I was moving towards you at before) , but I'm still moving at a pace per second...

[thehollowmen]

AND if you're not exceeding the speed limit you are even safer!! :2thumbsup

Oh I so agree with you there
:innocent:

me? speed?
my bike doesn't even go that fast

now can anybody change a rear sproket for me to make me go faster?

[scumdog]

From my understanding of radar, I dont think there are any angles involved. Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.

Eh? think of it this way ( you're not trolling are you?), a car is going from left to right at a 150kph, it is approaching at a 15 degree angle, the radar only measures at the CLOSING speed of said car, (i.e. straight towards the radar) hence the car only shows a speed of 25 kph.

[Mr Skid]

Just incase you thought I was serious, I can't even wheelie! :stupid:

You can't wheelie an R1? :spudwhat:

[badlieutenant]

Signal goes out, hits object returns. Also does not radar travel at a fairly good speed - compared to that - the car would be pretty stationary wouldnt it.
speed of light ? electromagnetic frequencies ?yer, and yer right, relative to the radar the object would apear to be stationary but I think it measures the rate of change of said signal to travel there and back each time, assuming its from the same object each time. or your just taking the piss................. :crybaby:

[scumdog]

speed of light ? electromagnetic frequencies ?yer, and yer right, relative to the radar the object would apear to be stationary but I think it measures the rate of change of said signal to travel there and back each time, assuming its from the same object each time. or your just taking the piss................. :crybaby:

At the risk of being trolled: Imagine you are God looking down on an airport and a bike is going from left to right on one side of the runway at 100kph at an angle approaching you of say 20 degrees, you are standing on the other side of the runway which is 100 meters wide.
The bike is doing 100kph, no question, it is crossing the runway towards you at a shallow angle taking 5 seconds to cross the runway. That means its approach speed in a straight line from you to it is 75kph.

i,e it is closing the gap to you at 75kph but because it is not coming directly at you it can be doing 100kph ground speed as it goes from left to right.

[badlieutenant]

God ! god! oooeeeerrr risky mate........... :bash:
simple pimple really, the shortest distance is a direct line from observer to object, so if object say has a set speed any variation off of the shortest path (straight towards the observer) will be measured as less that the constant speed the object actually is travelling at :D there, i think Lou understands now.
or am I trolling? lol :yes:
you guys should get together and smoke a fat :doobey: could film it for prosperity when one of you becomes the others boss....... :banana:
bring back the MOT and thier really kewl pants (dont know why they got refered to as nazis?)


*im changing my alias and moving to the hills*

[Lou Girardin]

isn't that what i said?

get a couple of matchbox cars out lou, and do the math in visual symphony, as obviously your tiny brain can't compute it without external input. if the vehicle being tracked (that's you) is travelling at an angle to the vehicle doing the tracking (that's the police - they're the ones in the patrol cars - can you say patrol?), then the cosine angle is advantageous to the vehicle being tracked. there is no circumstance when the radar will read HIGHER due to the angle, regardless if the patrol car is on a corner or on a straight.

Read it again, Marty. Then study traffic radar technology.
If the patrol car is closing the angle to the target the radar reads HIGHER. This is cosine ERROR, a litle different to cosine ANGLE.
A simple arrangement that has got a lot of Americans, where their lawyers understand these things, off a lot of tickets.

[James Deuce]

The only bikers I've ever chased are the types that stink real bad and wear patches on their backs. I've heard it heaps of times over the radio where a cop calls up to say that he just clocked a bike at 240'ish. Ask for a description....."I think it was a red one"! Roger, we'll keep an eye out for a red bike.

If you went past me like that I'd be saying, "There aint no way I'm going to catch that guy so I might as well enjoy the show".

PMPL!! On both counts. :niceone:

[TwoSeven]

I get what you guys are getting at - am I right in your talking about the hand held radar guns and the copper being on the side of the road.

Because the fixed point radar is aimed at the front/rear of the car and samples over a short period of time (you'd never have one set up to be more than 15 deg out). It just uses the time the signal takes to come back from the first sample with regards to the second sample - then works out the speed of the vehicle. The distance the vehicle needs to travel is very small, maybe about 10 centimetres or even less depending on the system.

The other kind is just a laser pointer that has a 1k range. And the final system is SPECs which takes a digital photo and does number plate recognition as well. Its very very accurate and usually operated in pairs (so it takes your average speed between points).

Its not the radar/laser thats the problem - its taking the photo that matches the vehicle to the data thats the issue (not sure if NZ requires photo evidence).

I worked with some folks a decade ago that were developing a system for use in UK jam jars. Basically think military grade stuff and I suspect its been well and truly improved by now.

[thehollowmen]

I get what you guys are getting at - am I right in your talking about the hand held radar guns and the copper being on the side of the road.


Some of those... also discussing the car mounted ones that are at an angle... ca n even do the speed cameras...


if you worked on them.. you could answer... they only measure the speed in the same plane that the radar gun / antenna is pointing... right?

[TwoSeven]

I dont really know much about the technicalities of how the actual 'lectronics work - i'm not a boffin. Just know about the s/w side of it - the bit that actually processes the data that the camera has gathered.

But since gatso and mini gatso cameras have to be set up pointing in a specific direction, i'd say they would use a fairly narrow 'beam' so to speak.

Radar is (I think) classified using a type number. A quick google shows gatso being type 24. Not sure what the stats is for that.

Being that they are usually pointed at the back end of a car moving away (or down a motorway lane) - i'd suggest they have a small angle.

[marty]

the camera vans/fixed sites are calibrated for the angle - i think it's 38 degrees

[marty]

i'm gonna be a whore soon!!!!

[thehollowmen]

i'm gonna be a whore soon!!!!

Congratulations

Those fixed ones.. can understand the calabration...

Now does the "cosign defense" work with people close to the camera or prople on the horizon? If they're on the horizon and it is calabrated for say 10 degrees out ..I can see why they think the car would be going faster than it is...

[scumdog]

Never heard of that 'defence' being used here, I wonder how much % error it allegedly creates?

[marty]

the camera is *always* set up at the calibrated angle to the road - you shouldn't see a camera van parked at too much of an angle to the centreline, and in fact it is part of the set up of the van that it is recorded as to it's parking location relative to the road - they use the simple 3/4/5 rule to set up i think. if you were to cross the c/l, and drive straight towards the camera then you may be able to fool it into thinking you're going quicker, but i am sure the photo wold get you into more trouble than just speeding.....

[thehollowmen]

Never heard of that 'defence' being used here, I wonder how much % error it allegedly creates?

Usually it works to the advantage of the speeding car... the closer it is to a car / hand mounted one the greater the angle and the smaller the reading..

the Sci am article had error rates up about 10 mph at 60 mph... for a car mounted one measuring the speed of a car in the next lane..

the cosign defence is more for when one has been calabrated "roadside" ... 10 or 30 degrees or whatever, and you get the cop standing on the corner pointing it directally up a straight so there is no angle... it will read high then

[thehollowmen]

the camera is *always* set up at the calibrated angle to the road - you shouldn't see a camera van parked at too much of an angle to the centreline, and in fact it is part of the set up of the van that it is recorded as to it's parking location relative to the road - they use the simple 3/4/5 rule to set up i think. if you were to cross the c/l, and drive straight towards the camera then you may be able to fool it into thinking you're going quicker, but i am sure the photo wold get you into more trouble than just speeding.....


That's true :-P
and I'm not advocating speeding or crossing the center line..

but what happens if you pull into a passing lane towards a speed camera? that's also a situation that might cause it to read high... Then again unless you're passing grandmas or old men wearing hats you would almost definitally be speeding...

Us bikers shouldn't have to worry about this though, these situations which get a false high reading are usually heading towards or directally away from the camera / radar detector... And our plate is on the back of the bike.

Heading directally away would mean we're heading off the road ;-)

[TwoSeven]

I dont think the accuracy of the units is reall important enought to be an issue. If it was i'm sure someone like Thales would have adapted a military grade radar. Now if you can detect and locate the correct postion of a artil. shell from 20k away - i suspect tracking a car would be pretty easy. :)

[Lou Girardin]

I dont think the accuracy of the units is reall important enought to be an issue. If it was i'm sure someone like Thales would have adapted a military grade radar. Now if you can detect and locate the correct postion of a artil. shell from 20k away - i suspect tracking a car would be pretty easy. :)

True, but don't think traffic radar is as sophisticated as military spec gear.
Accuracy may not sound important, unless your doing 147km/h and the radar reads 151. 28 days catching a bus.

[scumdog]

True, but don't think traffic radar is as sophisticated as military spec gear.
Accuracy may not sound important, unless your doing 147km/h and the radar reads 151. 28 days catching a bus.

Great one Lou - like you're going to know that you were ONLY doing 147kay when the cops tells you that you were doing 151kay? once again, -yeah right (gimme another Tui) :ar15:

[TwoSeven]

True, but don't think traffic radar is as sophisticated as military spec gear.
Accuracy may not sound important, unless your doing 147km/h and the radar reads 151. 28 days catching a bus.

But in most cases I suspect that the 'your nicked matey' would still apply in both cases.

Personally I dont really agree with fines as such. I think they are needed, but i'd much rather see points on licenses. 3 speeding offences should see you without a vehicle for some time.