Inside the Volkswagen emissions cheating

Posted Jan 7, 2016 10:29 UTC (Thu) by andy_shev (subscriber, #75870)
In reply to: Inside the Volkswagen emissions cheating by alonz
Parent article: Inside the Volkswagen emissions cheating

Luckily there is GPS system that doesn't lie, does it?

Inside the Volkswagen emissions cheating

Posted Jan 7, 2016 12:53 UTC (Thu) by NAR (subscriber, #1313) [Link] (2 responses)

The GPS usually shows 5-10% slower values. It practically means that if the speed limit is 50 km/h and the driver tries to keep the speed around the 50 km/h value (e.g. driving at 48-51) showed by the speedometer, then he's safely below the speed limit.

Inside the Volkswagen emissions cheating

Posted Jan 8, 2016 21:11 UTC (Fri) by ken (subscriber, #625) [Link] (1 responses)

Are you sure about that? From googling around I get the impression that GPS generally has less than 1% error on speed.

Lying speedometers

Posted Jan 10, 2016 0:55 UTC (Sun) by giraffedata (guest, #1954) [Link]

You misread the comment. It says the GPS reading, which is presumed to be correct, is 10-15% slower than the speedometer reading. So the speedometer overstates the speed and you cannot break the speed limit by driving by the speedometer.

Inside the Volkswagen emissions cheating

Posted Jan 7, 2016 17:47 UTC (Thu) by ssam (guest, #46587) [Link] (3 responses)

GPS will generally overestimate distance travelled due to jitter on each position reading.

Inside the Volkswagen emissions cheating

Posted Jan 12, 2016 11:42 UTC (Tue) by javispedro (guest, #83660) [Link]

GPS does not use position for speed -- Doppler shift is used for instantaneous speed. But even when you use position samples to calculate speed/distance, simple statistics (e.g. Kalman) filter the jitter out and obtain readings that will be more than accurate for the "car speedometer" use case.

Inside the Volkswagen emissions cheating

Posted Jan 12, 2016 12:53 UTC (Tue) by Sesse (subscriber, #53779) [Link] (1 responses)

Only as long as you're driving reasonably straight. If you take a lot of turns (e.g., city driving), you'll get the opposite effect.

Inside the Volkswagen emissions cheating

Posted Jan 28, 2016 16:38 UTC (Thu) by mathstuf (subscriber, #69389) [Link]

I used GPS to track a side trail on the map but not OSM last week. It's also almost comical with hiking with moderate tree cover (90 second interval to balance between accuracy and battery life). There are two quarter mile offshoots I definitely didn't do (they cross the contour lines all wrong). Still need to load it up in a GPX editor to overlap with the map to see how much of the GPX is useful before submission though.