Which one is more accurate ??

[204 Escape]

Police radar, or a GPS system ??

I own a NUVI 255W by Garmin, and was wondering which one was more accurate ??

 

[Shizzy]

Re: Which one is more accurate ??

when it comes to writing a speeding ticket, im sure the radar is the "accurate" one.....

 

[oops!]

Re: Which one is more accurate ??

from my understanding.....gps is one of "less" precice systems....gps allows a few yards either way.

 

[NoKlu]

Re: Which one is more accurate ??

Lots of guys are beating tickets because the radar guns are not calibrated properly. There should not be that much difference between the newer gps systems and a radar gun. We need details.

 

[slasmith1]

Re: Which one is more accurate ??

police radar comes in may forms but most state laws require them to be calibrated within +\- 3mph.

 

[Tacklewasher]

Re: Which one is more accurate ??

Police radar, or a GPS system ??

I own a NUVI 255W by Garmin, and was wondering which one was more accurate ??

My vote is on the radar.

I also have a NUVI 255W and love it, but would never think it could get me out of a ticket.

Funny thing is, the GPS has better accuracy on a boat than in a car. Problem with a car is any GPS has to do some math based on it's horizontal speed and any change in elevation. The GPS basically measures horizontal speed, but this is less than road speed if you are going up or down a hill. The GPS is good at taking the elevation change into account to calculate groundspeed, but poor sat coverage and just the fact that it has to do a calculation will generally make the GPS show slower than ground speed.

Put it in a boat on a nice calm day, no change in elevation so the results are more accurate.

But the radar will win every time.

 

[NoKlu]

Re: Which one is more accurate ??

I just found this and copied it from another site.
[SIZE=+2]GPS Speed:[/SIZE]
[SIZE=+2]How accurate is it? How fast can I go? How HIGH can I go?[/SIZE] GPS receivers display speed and calculate the speed using algorithms in the Kalman filter. Most receivers compute speed by a combination of movement per unit time and computing the doppler shift in the pseudo range signals from the satellites. The speed is smoothed and not instantaneous speed.
HOW ACCURATE IS THE SPEED READING?

From the NAVSTAR GPS User Equipment Introduction document Section 3.7:
GPS receivers typically calculate velocity by measuring the frequency shift (Doppler shift) of the GPS D-band carrier(s). Velocity accuracy can be scenario dependent, (multipath, obstructed sky view from the dash of a car, mountains, city canyons, bad DOP) but 0.2 m/sec per axis (95%) is achievable for PPS and SPS velocity accuracy is the same as PPS when SA is off.
Velocity measured by a GPS is inherently 3 dimension, but consumer GPS receivers only report 2D (horizontal) speed on their readout. Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on.
HOW FAST CAN I GO AND HAVE MY GPS READOUT MY SPEED?
All Currently manufactured CONSUMER GPS receivers we know about will measure speed to 999 miles per hour.
Garmin (uniquely as far as we know) manufactured the G-38, G-40, G-45, and the G-II (not PLUS) units which had a 90 mph speed readout limit. These units are manufacturing discontinued and we know of no other manufacturer who made a unit which would not go to 999mph.
HOW HIGH CAN I GO AND HAVE MY GPS READOUT ALTITUDE?
Defense department regulations prohibit standard consumer GPS receivers from functioning above 60,000 feet and 999mph (simultaneously). Most GPS receivers seem to set hard limits at EITHER 999mph or 60,000 feet.

 

[204 Escape]

Re: Which one is more accurate ??

Thanx, interesting read. I've noticed that my speedometer, and the gps, sometimes do NOT agree, exactly.

 

[JB]

Re: Which one is more accurate ??

GPS is more accurate than police radar.

As reported above in different posts, the RADAR spec is +/- 3mph, the GPS spec is +/- .1mph.

 

[Bob_VT]

Re: Which one is more accurate ??

As far as instant readings I believe that police radar is faster and there is a lag in GPS. Radar must be re-calibrated daily and the GPS is recalibrated when it initializes.



In my own car I have GPS, Scan Gauge and my Speedometer...... when I push down on the pedal the GPS is the last to register the speed. There is a lag.

 

[captharv]

Re: Which one is more accurate ??

During the 80s, I calibrated, certified, and repaired police RADAR. The units all were tested to+/- 1 MPH. The unit, being microprocessor controlled, was accurate to +/- 1/10th MPH, however, the readouts usually 1 MPH. The units actually take 5 readings about 1/10 of a second apart and compares them. The algorithym is set to look for explainible sequences like: 60, 60,59, 59, 58. If its sees a flyer, like 85, 60,60,60,60 it throws out the reading an refuses to display.
Basically put, the GPS and RADAR are about equal in accuracy. But, since we certified it accurate with 1 MPH, the judges will go by whatever the officer wrote on your ticket.
The only recourse you have is to ask for the calibration certificate and the training card with the officers initiail training and yearly re-certifications. If either was out of date when the incident occured, you win.
I sat thru 6 trials where the "speeder" contested the ticket.
Only 1 was aducated in favor of the speeder. the rest paid the ticket AND court costs of $150
As Davy Crocket ( the Disney one) used to say:"Be sure you are right and then go ahead".

 

[Nandy]

Re: Which one is more accurate ??

If you are looking to get out of a ticket the gps speed will not help you. If the police officer is properly certified and the radar gun has been calibrated as required you have no way out. To the judge, the radar gun is better than the gps...

If you are looking at the gps speed and your speedometer I will say the gps is more accurate.

 

[puddle jumper]

Re: Which one is more accurate ??

I'm going to ask the obvious question. How fast were you going when you got pulled over.And im going to say in the Court of law THE RADAR GUN.

 

[JB]

Re: Which one is more accurate ??

Was doing 61.5 GPS (63 speedo) when pulled over and ticketed for 70mph.

Was doing 68.8 GPS (70 speedo) when pulled over and ticketed for doing 74mph.

Not guilty both times because of situations that caused RADAR to be in error.

 

[ob]

Re: Which one is more accurate ??

I rarely see any vehicles pulled over for speeding 10 mph or less over the posted limit unless the infraction was in a school zone.Traffic in many cases flows faster than the posted limit by 5 or more mph.I'm certain there are officers that pull people over for slightly above the posted limit , but in my experience it is not typical.That said... I would think in most cases that a 2-4 mph descrepancy beteween the police radar and driver gps wouldn't help much in the way of technologying oneself out of a fine.

 

[JB]

Re: Which one is more accurate ??

As in any adversary proceeding in a court of law. Too often it is not about truth, it is about winning.