The Wikipedia article on GPS has a lot of info. The Official source of info would be: http://www.gps.gov/technical/
Lots of technical PDFs there! I used the Interface Control Document IS-GPS-200 and SPS Performance Standard Specification, mostly the latter. In short, though, the GPS comms cycle involves sending 25 pages of data at 50bps. Each page takes 30sec to be received and contains the complete ephemeris for the satellite and 1/25th of the almanac. 25*30sec = 12.5 minutes. One of the almanac pages contains the GPS/UTC correction. All satellites transmit the same almanac, which is good for several days. Each satellite transmits its own ephemeris, which is good for a few hours. Receivers will frequently store this info for faster startup. Devices with Internet capability (say, Android smartphones :-) can download everything from the Internet. I should mention that all satellites appear to transmit the almanac in sync. I never saw the GPS/UTC correction message any faster than every 12.5 minutes no matter how many satellites were visible. The problem for timing is that there is no way to tell what GPS/UTC offset is actually being applied by the receiver. I have not seen any comms protocol that includes this info, not NMEA, not SiRF. Android limits your options. There is simply no way to be *sure*. The best I could come up with was listening to the raw data, but you can't do that on Android. -- Andrew -- You received this message because you are subscribed to the Google Groups "Android Developers" group. To post to this group, send email to android-developers@googlegroups.com To unsubscribe from this group, send email to android-developers+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/android-developers?hl=en
