Apparently the database in my area is poor. Another location I am sometimes found in is *Fremont*, almost 100 miles southeast. Fremont most frequently shows up as the "closest store" when I am looking at (for example) hardware store web sites.
Jeremy N6WFO On Wed, Mar 14, 2018 at 10:15 AM Bob kb8tq <[email protected]> wrote: > Hi > > WiFi based location can be pretty good or it can be a real joke. It all > depends on > how good the database happens to be and how many stationary WiFi setups you > can “see”. I’ve had it pop up with locations that are off by many miles. > ISP’s > feed you IP addresses via DHCP and the “on net” numbers are rarely visible > to > the casual passerby. , They likely are depending on other information > (like SSID > surveys from vehicles). > > Bob > > > On Mar 13, 2018, at 11:15 PM, Bill Byrom <[email protected]> wrote: > > > > Have you noticed that your mobile devices (smartphone, iPad, tablet PC, > > laptop PC) can often know your location when you inside a building > > shielding you from GPS satellites (or producing multipath confusing the > > GPS receiver)? Here is a quick test you can do if you have a PC with no > > GPS receiver but with WiFi capability: > > Start up a browser and go to http://maps.google.com (which redirects to > > https://www.google.com/maps/...) with a WiFi connection. Near the lower > > right of the screen you should see the + - zoom buttons, and above these > > a target icon. Click that target icon. If asked, enable location > > finding. You may also need to enable your browser to release location > > information. In my case, I am now sitting near the middle of my house > > and the laptop Windows 10 PC Google Maps locator places my location on > > the street adjacent to my house, about 25 meters or so from my actual > > location. My iPhone iOS map shows my location more closely (inside my > > house) and it very accurately shows the location of the minivan I parked > > in the driveway several hours ago (as "parked car"). My iPad also shows > > my location within my house. > > How do these devices know your location without GPS? Several methods are > > used to produce a hybrid positioning system[1]:(1) Your IP address from > your ISP. This gets me within a few km of my > > location. See: https://www.iplocation.net/(2) WiFi positioning > system[2] - This makes use of databases which > > contain the geographic location of WiFi access points. The data is > > collected by methods such as comparing the GPS receiver location > > reports of mobile devices with the signal strength of access > points.(3) Cellular radio location - Various techniques allow accurate > > mobile phone tracking[3]. The signal strength and propagation > > delay from cellular base stations allow moderately good > > determination of location. > > If you are in an area without GPS receiver coverage, your mobile device > > or PC can determine the time using various techniques:(1) Crystal > oscillator for short-term time stability. > > (2) NTP: https://en.wikipedia.org/wiki/Network_Time_Protocol > > (3) Cellular timing - cellular phone networks require very accurate > > timing of the RF signals. > > It would be hard to place terrestrial transmitters on the GPS satellite > > frequencies without dynamic range and other problems, and of course > > someone could use this technique to jam GPS reception in an area. But > > several terrestrial geolocation and timing dissemination systems have > > been proposed, and some limited deployment has been achieved. > https://en.wikipedia.org/wiki/NextNav > > http://www.nextnav.com/technology > > http://esatjournals.net/ijret/2013v02/i04/IJRET20130204031.pdf > > > https://spectrum.ieee.org/tech-talk/telecom/wireless/us-master-clock-keepers-test-ground-alternative-to-gps-- > > Bill Byrom N5BB > > > > > > > > On Tue, Mar 13, 2018, at 5:17 PM, Stewart Cobb wrote: > >> Peter Reilley suggests a backup to GPS using terrestrial > >> transmitters. This> idea has been around since the early days of GPS. > The terrestrial > >> transmitters were called "pseudo-satellites", or "pseudolites" > >> for short.> The big problem with this idea is that the GPS signal > format has > >> a narrow> dynamic range. The signal strength from a terrestrial > >> transmitter varies> widely (inverse square law) from positions near the > transmitter to > >> positions far away. The variation in any practical system is > >> larger than> the GPS signal format can handle. This is called the > "near-far > >> problem".> For an extensive discussion of the pseudolite concept, > including the > >> near-far problem, see my dissertation. You can find it with a > >> web search> for my full name and the word "pseudolites". > >> > >> Cheers! > >> --Stu > >> _________________________________________________ > >> time-nuts mailing list -- [email protected] > >> To unsubscribe, go to > >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> and follow > the instructions there. > > > > > > Links: > > > > 1. https://en.wikipedia.org/wiki/Hybrid_positioning_system > > 2. https://en.wikipedia.org/wiki/Wi-Fi_positioning_system > > 3. https://en.wikipedia.org/wiki/Mobile_phone_tracking > > _______________________________________________ > > time-nuts mailing list -- [email protected] > > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Sent from my iPad 4. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
