Watches your speed and works out the moment you stopped driving and walked away. Nothing leaves the phone — positions stay in this browser.
Mapped lots where no permit or payment is needed at this hour, from Stanford's default enforcement times and university holidays. A posted sign wins, and event days (Frost, the stadium) are not known here.
A car stopping is not a car parking. The thing that separates a red light from a parking spot is that you get out and walk away. So the detector waits for all of this before it believes you:
1. Sustained vehicular speed for at least 25 s — above
6.0 m/s (~21 km/h) reads as a car, 2.8–6.0 m/s as a
bike. 2. Speed drops to walking or below, which opens a candidate at the
last vehicular position. 3. You stay non-vehicular for 75 s
and get at least 25 m from that spot. Only then is it
recorded.
Driving again before step 3 cancels the candidate, which is what rejects red
lights and stop-and-go traffic. Sitting in the car for twenty minutes does
not cancel it — the car is still where you stopped. What does cancel it
is a gap in the data over 15 min: if fixes stop arriving we
cannot promise the car did not move, so we admit that instead of guessing.
Fixes with accuracy worse than 60 m are thrown away, and speed is
median-smoothed over 5 samples so one GPS spike cannot fake a journey.