Manu EL <[email protected]> writes: > I've done some testing. I use GPS only, no A-GPS. Mobile connection is off > (airplane mode). > > Testing > In the village (900m above sea level) : everything is fine with the GPS. > In the mountains (> 1000m) : I start the smartphone. I open 'GPS Test' app => > I get a GPS fix. Then I put the app in the background or lock the screen, > then I reselect the app => impossible to get a fix > Same behaviour with Osmand. Same when I close the app and then relaunch it.
These are not particularly high elevations, relative to GPS functionality. I've been to 3000m and spent days over 2000m with no GPS trouble. > Workaround 1 > In GPS Test, I go in the A-GPS menu, do 'clear cache' or 'clear & > update'. Still no fix in GPS Test. But if I send GPS Test in the You say "no fix", but I wonder how long you are waiting. With a clear sky view, you should generally start to track satellites within a minute, often much faster. For each, once you have received it for 30s solid it can be used in a fix. In GPS Test, you'll see flags for each satellite (text view, "Status"). I typically see "AE" for satellites not used in the fix, and "AEU" for those used. A is for Almanac (long term, lets you find satellite roughly in terms of is it above the horizon and doppler shift) and E is for Ephemeris (precise orbit, good enough to compute position). Almanac lasts for weeks, and Ephemeris is good for a few hours. You can tell if the satellite is being received by a non-blank C/N0 field. Generally, reception with reasonable strength (>15?) and E leads to usage in the fix. For GLONASS satellites, I see A if not tracked and AEU or AU for those being tracked. A-GPS will speed this up. As I understand it, mostly getting you the per-satellite precise orbits right away, instead of having to receive for 30s. I have never heard that A-GPS matters much if you can sit still for a few minutes with a good sky view. For me, I seem to get E for GPS, and not for GLONASS. So I wonder what you are seeing while waiting: are satellites showing up with non-blank C/N0? Do any have "AE" or "A"? A screenshot would be interesting if you are willing to share. > background then select Osmand, I get a fix after 1 minute in Osmand > (would be the same with GPS Test : if I send GPS Test in the > background then reselect GPS Test, I get a fix after 1 minute in GPS > Test). This workaround can be used in emergency but is not > convenient. My hypothesis is that the GPS cache is somehow corrupted > when the app is sent to background or closed. Any app launched at this > point will fail to get a fix, until the GPS cache is cleared. If so this sounds like a bug in your particular phone's operating system. > Workaround 2 > In Osmand, I start a trace recording with recording interval set to 3 > minutes (to preserve battery). From this point, I can send Osmand in > the background or lock the screen without losing the GPS fix. It may > consume a bit of battery, but at least, I can use the GPS in > mountains. That's great. > > This is a strange bug, considering it happens only in altitude, or depending > on some other parameters I'm not aware of. > > If anybody thinks about a real fix for this issue, please tell me!! Perhaps file a bug with your the maintainer of your phone's operating system. Also, I have seen phones get excessively warm partly from GPS, and partly trying to find cell towers that aren't there. But you said airplane mode, so that should keep power usage from the cell modem zero/low and thus not heat up. -- You received this message because you are subscribed to the Google Groups "Osmand" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/osmand/rmiwof95px8.fsf%40s1.lexort.com.
