Hello all....
In terms of your vehicles speedometer and your GPS speed reading.... which one would reflect on the laser gun? which is more accurate?
Lemme no...
Hello all....
In terms of your vehicles speedometer and your GPS speed reading.... which one would reflect on the laser gun? which is more accurate?
Lemme no...
generally.....
1. Speedos are usually 10 percent over.
2. GPS units lag behind depending on the efficiency of the chipset computing your location but are generally more accurate if you maintain a steady speed.
So keep a steady speed and your GPS will be the more accurate
Thanx but that does not answer whether the laser guns speed reading is closer to GPS speed or speedometer speed???
In general, GPS speed would be closer to what a police radar/laser gun would read, unless your speedometer is calibrated and accurate (most aren't).
That said, GPS speed tends to lag, so it's only accurate if you've been going the same speed for a little while. If the GPS reads 75, then you slow down or speed up and then get lasered immediately afterward, the laser will read your new speed while the GPS might still have your old speed.
Also, GPS gives you an average speed over a period of time (say, 5 seconds). The laser will give the LEO your speed at the instant the laser takes a reading. But if your speed is steady, the GPS should give the same speed as the laser.
If I'm passing you on the right, YOU are in the wrong lane!
If speed kills, how come I'm still alive?
Active Countermeasures: V1 3.858, Escort Redline, Beltronics STi-R+, LI Dual 7.1x CPU/8.7 Heads (front)
Other/Backup Countermeasures: V1 3.813 (loaned to friend), Beltronics Pro RX65 M4 6.3
Vehicle: 2002 Audi A4 1.8T Quattro
LEO Toys: Kustom Pro Laser II & III
Encounters/Saves August 2011: Radar 3/1, Laser 0/0
Of course it does!Originally Posted by anjoem
Laser guns speed should be very close to your true speed if it is being used properly.
Since GPS is more accurate than your speedo, then the laser gun reading should be closer to your GPS speed reading.
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.
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.
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.
-----------------------------------------------------------------------------------------
This reflects my own observations. I used a lasergun from my car while driving, measuring against traffic signs. This gives you the speed of your own car. GPS readings always perfectly matched the lasergun readings.
Next to fulcrums post, How can anyone determine which is More accurate?
GPS runs an average. Its data feed isn't THAT instantaneous....
Speedometer can be very accurate, or way off. Saying that, which do you want to tie your LIDAr reading to: An accurate speedo or an inaccurate one?
the Q baffles me. The LEO will ticket your vehicle if the LIDAR shows a high enough reading. relevant to what seems to be your Q.
Time over distance would be the most accurate, although its an "average" reading (over the distance), not instantaneous, but hardest to defend against in court IMHO.
Speed (reading) over 1500 feet (in distance traveled) or so, would be a tough cookie to crack.
-Suf Daddy
Bookmarks