Re: Influence of WiFi on GPS readings (200m error)
I've had this problem when the initial fix was obtained while I'm inside a vehicle (such as a bus or car) or near a lot of metal. Going to a complete stop, then moving a few times (in the car) seems to give the chipset a better chance to realize it's got a bogus fix. -Rusty Yaroslav Halchenko wrote: Hi All, Finally I got to play with FR. Flushed todays (0721) dev image and kernel. Running TangoGPS. While WiFi is on (WEP encrypted. wpa_supplicant powered ;)) I am having location error (never hit the right spot) around 200-400m with reported speed from 0.5 to 20 km/h (while I am siting steadily in 1 place). When I turn WiFi Off (just on my FR, without touching access point or a laptop from which I am writing) -- location moves to the right spot with a bias of 10m or so. Therefore, the question: is that expected? ie that we can't rely on GPS readings while WiFi is on? Or from the other side: what is 'documented' precision in GPS readings while WiFi is enabled (and not actually very actively used, if used at all since I guess TangoGPS already had those tiles from OSM downloaded). Or may be it is just my FR which behaves that way? Did anyone observe any similar behavior? ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: Influence of WiFi on GPS readings (200m error)
I'm not sure where the fault lies, but with tangogps, I seem to get a scatter plot displayed for my position. Initially the fix seems accurate, then it starts to wander, although I may not be. If I am moving, the trial doesn't seem to follow the route I've taken. I think it may be tangogps, but I thought I'd try using my garmin bluetooth in a side by side kind of test to see whether it is tangogps or the gps radio. Chris On Jul 21, 2008, at 12:02 AM, Russell Sears wrote: I've had this problem when the initial fix was obtained while I'm inside a vehicle (such as a bus or car) or near a lot of metal. Going to a complete stop, then moving a few times (in the car) seems to give the chipset a better chance to realize it's got a bogus fix. -Rusty Yaroslav Halchenko wrote: Hi All, Finally I got to play with FR. Flushed todays (0721) dev image and kernel. Running TangoGPS. While WiFi is on (WEP encrypted. wpa_supplicant powered ;)) I am having location error (never hit the right spot) around 200-400m with reported speed from 0.5 to 20 km/h (while I am siting steadily in 1 place). When I turn WiFi Off (just on my FR, without touching access point or a laptop from which I am writing) -- location moves to the right spot with a bias of 10m or so. Therefore, the question: is that expected? ie that we can't rely on GPS readings while WiFi is on? Or from the other side: what is 'documented' precision in GPS readings while WiFi is enabled (and not actually very actively used, if used at all since I guess TangoGPS already had those tiles from OSM downloaded). Or may be it is just my FR which behaves that way? Did anyone observe any similar behavior? ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
Re: Influence of WiFi on GPS readings (200m error)
On Mon, 2008-07-21 at 07:54 -0700, C R McClenaghan wrote: I'm not sure where the fault lies, but with tangogps, I seem to get a scatter plot displayed for my position. Initially the fix seems accurate, then it starts to wander, although I may not be. If I am moving, the trial doesn't seem to follow the route I've taken. I think it may be tangogps, but I thought I'd try using my garmin bluetooth in a side by side kind of test to see whether it is tangogps or the gps radio. tangogps just uses whatever comes from the GPS chip. No mangling whatsoever. You can test it by just dumping the output of /dev/ttySAC1 to a logfile, convert it to GPX or KML and use it with Google maps. The u-blox chip is quite jittery (extremly so when used with an SD card without the fixes, be it kernel or additional capacitor). Additionally in a city the accuracy of any GPS while driving or walking will deviate up to 50m from your real position. Just have a look at openstreetmap GPX traces for various cities... The performance of the u-blox chip (without an SD card) is impressive - apart from that flaw the hardware guys at openmoko have done an excellent job. Last word about the jitter: most GPS chips support different modes, one where they flatten out the GPS signal and a 'straight' one. Have a look into the u-blox binary protocol and you will most likely find something there to switch - I know that SIRF has something to this account. The Globallocate chip in the Neo 1973 does flatten by default. However, you need to go between 10m and 20m before it starts to 'believe' that you move. The u-blox tells you after 3-4m. Marcus Chris On Jul 21, 2008, at 12:02 AM, Russell Sears wrote: I've had this problem when the initial fix was obtained while I'm inside a vehicle (such as a bus or car) or near a lot of metal. Going to a complete stop, then moving a few times (in the car) seems to give the chipset a better chance to realize it's got a bogus fix. -Rusty Yaroslav Halchenko wrote: Hi All, Finally I got to play with FR. Flushed todays (0721) dev image and kernel. Running TangoGPS. While WiFi is on (WEP encrypted. wpa_supplicant powered ;)) I am having location error (never hit the right spot) around 200-400m with reported speed from 0.5 to 20 km/h (while I am siting steadily in 1 place). When I turn WiFi Off (just on my FR, without touching access point or a laptop from which I am writing) -- location moves to the right spot with a bias of 10m or so. Therefore, the question: is that expected? ie that we can't rely on GPS readings while WiFi is on? Or from the other side: what is 'documented' precision in GPS readings while WiFi is enabled (and not actually very actively used, if used at all since I guess TangoGPS already had those tiles from OSM downloaded). Or may be it is just my FR which behaves that way? Did anyone observe any similar behavior? ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community ___ Openmoko community mailing list community@lists.openmoko.org http://lists.openmoko.org/mailman/listinfo/community
