Mr Greed

Have a look at this site. Unfortunate url but you get the drift. Not a bad read if you get the chance.

Regards,
MG>

Go to:
www.speedingisbullshit.com

__________________
liar, li-er, n. one who tells lies, esp. habitually. Steve Bracks, Carl Scully and Bob Carr, MUARC.
nepotism, nepp-oh-tiz-em, v. the act of giving jobs to your mates, particularly to mis-represent the will of the people and promote your own lies. Pedestrian Council of Australia (PCA), Harold Scruby, NSW RTA Road Safety group, NRMA.

Dellboy999

Bit 'one' eyed that site, but what would you expect with a title like that

__________________

flagship042

Interested to note the article regards the GPS. Was pulled over by the cops in Gol Gol NSW recently for doing 72kph (so they said) in a 50kph zone.
I disputed the alledged speed and indicated that the trip log in the GPS would give a far more accurate figure than their radar ever would. The younger policeman present disputed this fact and when I asked him to explain the GPS system and on which scientific facts he was basing his argument on, he was not able to respond in the appropriate manner. To save face I got the standard lecture about speeding in town and was let go without the issueing of a fine.

Dellboy999

A GPS being more accurate then a sealed callibrated police radar, what will they think of next (insert sarcasm at the GPS here)

__________________

YOOT

Actually, there is no way a radar is as accurate as anything else. Because (as a surveyor) I know a lot baout EDM measuring, and to measure the accurate speed of a vehicle you need an accurate distance, and accurate time stamped to that distance measurement.

There is always going to be a delay between when the energy from the gun is bounced back and accurately measured (its not instant) it takes a number of seconds. Once the phase difference is solved repeat measurements can me made but there will always be around 0.5sec to 1sec delay.

Also, I know I can't measure a distance to high accuracy without a prism, and over 200m you need multiple prisms because the engery beam is so wide you're not receiving all of it back.

In DR mode (reflectorless, ie no prism) I can measure theoretically up to 200m but, it accuracy is 100 times worse and erratic. If you are not perpendicular to a flat surface, then the point at which the energy reflects back at you from is unknown, since the high energy beam needed to measure such things is messy and wide.

SO how the **** can a police officer hold a EDM measuring device of any description and bounce it off the irregular shape of a moving vehicle, at an angle and at such great distances and tell you EXACTLY how fast you are going? Quite simply, you can't. And thus most speeding fines are bullshit. Thats also not taking into account the humidity, pressure and temperature of the air of which large variations will occur if these are not taken into account.

GPS is no better over a short distance unless you solve the integer ambiguity and have some sort of base station setup to narrow down you position to sub 20mm accuracy.

Handheld and in-car systems don't solve jack shit, they are accurate to 10m which means you could be within 10m in any direction at any time from the geographical coordinate derived by the GPs device. Over a large distance 10m because insignificant, but typically police officers measure your speed over less than 100m of travel, so 10m is a large 10%.

__________________

Dellboy999

Speed detection – radar and lidar

Radar traps have been the bane of many a lead-foot’s life since the early 1960s. More recently, laser speed guns – lidar – have added a new dimension to speed-limit enforcement.

Radar

First coined during World War II, the term radar stands for ‘radio detection and ranging’. Using it to measure distance is pretty easy. High-frequency radio waves, a type of electromagnetic radiation, are transmitted towards the object of interest and are reflected back. We know that radio waves travel at the speed of light – about 300 million metres per second. If we know the time taken for the radio wave to reach the object, bounce off, and arrive back at the radar device, we can calculate the distance to the object (using the formula: distance = speed of light × time between emission and reception ÷ 2).

Measuring the speed of the object is a little trickier and relies on something called the Doppler effect. This was first proposed by Christian Doppler in 1842. He realised that the pitch of a sound emanating from a moving source varies for a stationary observer depending on the speed of the source and the direction in which it is moving.

Imagine you are on a train in a station and you can hear the signals ringing at a rail crossing just down the track. Since both you and the signals are stationary, the signals sound normal. They continue to ring at the same rate as the train starts to move, but now because you are travelling towards them they seem to get faster. In effect, the time between arrival of pulses of sound is being compressed (or shortened) and the apparent frequency is increasing. The result is that the signals sound higher-pitched. This change in frequency is called a 'Doppler shift'.

The radio waves emitted by a radar device propagate ******ds at a predetermined frequency. When they strike a moving vehicle and are reflected, the frequency is 'shifted'. The radio waves bounce back to the radar device, where the change in frequency is recorded and used as data in a formula that calculates the vehicle’s speed.

Radar used from the roadside usually employs something called ‘slant beam’. This means that the radar beam is projected across the road at a pre-set angle; speed is still determined using the Doppler shift. Slant beam radar is used in speed cameras (although some speed cameras use laser guns); slant beams were first introduced in 1991 and are now commonplace around Australia. Attached to the radar or speed gun is a camera that is activated when a vehicle exceeds the speed limit. The re******t photograph records the numberplate of the vehicle, along with the date, time and speed travelled.

The radar device need not be stationary itself: it is the relative movement between the radar and the targeted vehicle that is important. Radar devices are often mounted on patrol cars, the speed of which can be determined from the Doppler shift against stationary objects such as houses or trees. The speed of the targeted vehicle can be determined simply by calculating the net speed after deducting the speed of the patrol car.

Lidar

Laser speed guns – known as lidar, or ‘light detection and ranging’ – also use electromagnetic radiation. The term laser stands for ‘light amplification by stimulated emission of radiation’. Lasers are devices that can control the way energised atoms release photons of light: these photons form a very narrow beam of light.

The narrowness of this light beam gives rise to the label ‘speed gun’, because it must be aimed at the vehicle by the operator. When the trigger is pulled, the gun sends an invisible infrared laser light pulse. It then records the time it takes for the pulse to strike the target and return to the receiver mounted on the gun. From this time it is possible to calculate the distance to the object (range) in the same manner as for radar. The gun sends out hundreds of pulses per second; if the target is moving in respect to the laser, then the rate at which the distance to the target is changing is used to derive the speed of the target from a number of successive range measurements. The speed of the target is then displayed to the operator.

All laser guns in operation in Australia are tested to ensure that the laser light being transmitted complies with the appropriate Australian standard so that it cannot injure a person's eyes if they happen to look directly into the beam. This is done using an optical power meter certified by the National Measurement Laboratory with a certificate issued under the National Measurement Act.

The accuracy of all radar and lidar instruments to measure range and speed is tested using equipment called a delay generator, which must also be certified under the National Measurement Act.

The measure of success

In the early years of radar, many people caught speeding contested the scientific basis of the evidence. These days, the courts rarely entertain such challenges. The science, while still evolving, is sufficiently sound to satisfy most objective judges. And the reliability of the instruments can now be verified. That’s probably bad news for speeders – but good news for road safety.

SOurce: http://www.science.org.au/nova/060/060print.htm

__________________

YOOT

Wow, a generalised pile of semi-fact, no science or proofing of the physics behind measurement, just little statements of fact.

Did you know at 400m ther is also a very tiny amount of earth curvature to be taken into account, LOL!

Just remember for every meter that a speed gun is out, you could be told you were going 3.6kmh faster than you actually were, vice-versa it work in your favour.

__________________

Mr Greed

The fact is that our beloved Police and their legal cohorts prancing around as Police prosecutors (normally only a stiff Senior Constable for traffic matters) have the protection and benfit of years of legal legislation that has evolved to the point where unlike any other area of law you ARE guilty until proven innocent. It is strangely different from what most people believe because the Police simplay say we clocked idiot at xxx and used LIDAR and blah blah. You then have to prove this is incorrect.

That's why you can almost blow a barrister over with a feather if someone wins a speeding or other traffic matter on a facts case. It's like throwing hundred dollar bills at a fire, often you just get warm, but sometimes you might get a spark that changes the scenery!

Anyhow, in my experience forget about fighting the LIDAR or the RADAR. If you do it should merely be to extend the case long enough to introduce a technicality on which a good legal counsel can get the charges dismissed on.

Faced with the above, and yet again, an unsophisticated member or our Victorian Police force who'd rather munch donuts was the one looking for a plea bargain on a recent LIDAR case. They hate losing because the $3000++ costs of having a barrister fight a technical case hurts their KPIs.

Mr Greed.

__________________
liar, li-er, n. one who tells lies, esp. habitually. Steve Bracks, Carl Scully and Bob Carr, MUARC.
nepotism, nepp-oh-tiz-em, v. the act of giving jobs to your mates, particularly to mis-represent the will of the people and promote your own lies. Pedestrian Council of Australia (PCA), Harold Scruby, NSW RTA Road Safety group, NRMA.