4 ms·
Probably cheaper in terms of battery life to just use NTP than to periodically get a GPS fix.
by monochromatic 9y ago
Probably cheaper in terms of battery life to just use NTP than to periodically get a GPS fix.
- Piskvorrr 9y agoOf course. I was thinking "when another app is requesting a GPS fix anyway, might as well use the temporal part, as you're getting it for free."
- Dylan16807 9y agoIt's worth noting that to get time with .1s accuracy you don't actually need a GPS fix, just to pick up the 50-bit-per-second navigation signal for a couple seconds, from one satellite.
- monochromatic 9y agoHow would that work unless you know the distance to the satellite?
- p1mrx 9y agoIf you're on Earth, you can assume that the satellite is closer than 30000 km or so. Light takes 0.1s to cross that distance.
- Dylan16807 9y agoThe distance to an overhead GPS satellite is somewhere in the range of .07-.09 light-seconds. The planet's width is basically irrelevant when your goal is .1 second accuracy.
- nucleardog 9y agoBased off of some quick and dirty calculations for a GPS satellite at approximately 20,000km above sea level, the difference in distance between a satellite directly overhead and one straight out over the horizon is around 5500km. That's actually only about 18ms difference in delay. Unless there's something I'm failing to account for here, you should be able to get more than 0.1s precision based off of a single satellite's signal. Subtract a flat ~75ms to account for the minimum delay (~66ms @ 20,000km) and half of the variable delay, and you shouldn't really be more than about 9ms out.