Accuracy of GPS derived speed in stop and go traffic?

[fjparks]

Hi All,
Any input as to how accurate the speed is from GPS equipped dash cams?
Should be very good for steadily maintained speeds but it seems like that for acceleration / deacceleration in stop and go traffic that the number of GPS samples would have to be high to get accurate speed.
I'm specifically looking at the A129+ and I don't see it spec'd on the VIOFO site.
Thanks

 

[Nigel]

1Hz update, but then it is filtered to remove noise so there is a bit of a delay when accelerating/decelerating. Normally you don't spend much time accelerating/decelerating hard though, so it is fairly accurate most of the time, probably no more than 1mph out, and you can work out the rest from what is happening. At times of poor signal there can be several mph of variation, but on average it will be correct.

 

[SawMaster]

Dashcam GPS is rather basic and slow to process the data, so there's always a 'lag' or delay in displaying speed. I've compared 2 GPS-equipped cams against my ancient GPS device, and also against my van's speedometer which I have verified the accuracy of with calibrated police radar, and all are within 1MPH of each other in steady-speed driving.

Most courts will not accept GPS data as exactly accurate for legal purposes, such as contesting a speeding ticket, so it's value in a dashcam is mostly limited to keeping your cam's time/date settings updated automatically. True speed can be determined by a time/distance measurement on-scene and location can almost always be determined from the video images. Nice if a cam has it, not much lost if it doesn't

Phil

 

[kamkar]

No court will take dashcam speed into account as based on the GPS in the camera, but your exact speed can always be determined by the video itself as a result of the time it take you to cover a given distance one can go measure.
This could for instance be the distance between two lamp posts or signs / whatever along the road, and you can see by the video it took you X.XX seconds to cover XX:X feet, add a little math and you have your exact MPH speed.

Even in the little car i drive i can out accelerate the GPS speed, and if i brake hard by the time i am stopped my speed are always XX KMH, it is the same with my phone GPS i often use in combination with a waze like APP to know where mobile speed traps are reported to be ( Denmark only have 10 fixed speed traps but around 100 mobile ATC vans ( Automated Traffic Control )
I always use my GPS speed on the phone, and i have yet to get a speeding ticket, and i always go past a ATC van at the speed limit.