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There's an edge case in the GPS spec that only comes up every 20 years. It's well-documented and everything, but it only comes up every 20 years and software is
by jtolmar 8y ago
There's an edge case in the GPS spec that only comes up every 20 years. It's well-documented and everything, but it only comes up every 20 years and software is terrible, so not every GPS unit is going to handle it well. Last time this happened, GPS wasn't nearly as widely used.
I would expect some percent of phones to flip out (try force restarting, or waiting a day and restarting). Which ones are a mystery - the GPS chip in a phone isn't even consistent for a particular model.
I wouldn't expect planes to fall out of the sky. I wouldn't be surprised by flight delays though; just because the safety critical stuff is well tested doesn't mean the rest is.
And the errors aren't going to be confined to April 6th. We're talking about software bugs here, and it's dealing with a number that counts in weeks. So while bugs should center on the 6th, anything within a week of that is pretty plausible too.
(I wrote the GPS tracking algorithm used for navigation in Google Maps. Nothing above is based on Google-specific knowledge. It's still just someone's opinion.)
- jimktrains2 8y agoWhy would phones use the GPS date over the cellular-provided date?
- jtolmar 8y agoThe GPS unit needs to figure out the locations of all the satellites before it can use them to figure out your positions. The satellite positions are expressed as a function of time, and the times used are measured in seconds within the current GPS week[1]. This is the mechanism that I'd expect someone messed up. I'd expect location errors more than time errors, but because you can get time out of GPS then someone probably has. [1] https://gssc.esa.int/navipedia/index.php/GPS_and_Galileo_Satellite_Coordinates_Computation https://gssc.esa.int/navipedia/index.php/GPS_and_Galileo_Sat...
- elfchief 8y agoThe week number is (somewhat) used for navigation, but the way it is used is not affected in any way by the rollover, and there's not really a way (even taking into account bugs) that not knowing what the current GPS epoch is could affect navigation. This is purely a matter of an issue with the time that's output for human consumption, the GPS functionality itself doesn't care in the least.
- nyc111 8y agoI asked the same question above but since you actually wrote GPS code I thought I ask you too. Is it possible for me to find the actual line of code operators use to correct for General Relativity? I'm curious to know if this is a myth or if it is true. Thanks.
- TickleSteve 8y agoanswered above.... every GPS chipset does this.