问题
Right this is confusing me quite a bit, i'm not sure if any of you have noticed or used the "my location" feature on google maps using your desktop (or none GPS/none mobile device). If you have a browser with google gears (easiest to use is Google Chrome) then you will have a blue circle above the zoom function in Google Maps, when clicked (without being logged into my Google Account) using standard Wi Fi to my own personal router and a normal internet connection to my ISP, it somehow manages to pinpoint my exact location with a 100% accuracy (at this moment in time).
How does it do it? they breifly mention it here but it doesn't quite explain it, it says that my browser knows where i am...
...i am baffled, how?
I am intrigued because I would love to integrate it in the future of my programming projects, just like some background understanding and it doesn't seem too well documented at the moment.
回答1:
I am currently in Tokyo, and I used to be in Switzerland. Yet, my location until some days ago was not pinpinted exactly, except in the broad Tokyo area. Today I tried, and I appear to be in Switzerland. How?
Well the secret is that I am now connected through wireless, and my wireless router has been identified (thanks to association to other wifis around me at that time) in a very accurate area in Switzerland. Now, my wifi moved to Tokyo, but the queried system still thinks the wifi router is in Switzerland, because either it has no information about the additional wifis surrounding me right now, or it cannot sort out the conflicting info (namely, the specific info about my wifi router against my ip geolocation, which pinpoints me in the far east).
So, to answer your question, google, or someone for him, did "wardriving" around, mapping the wifi presence. Every time a query is performed to the system (probably in compliance with the W3C draft for the geolocation API) your computer sends the wifi identifiers it sees, and the system does two things:
- queries its database if geolocation exists for some of the wifis you passed, and returns the "wardrived" position if found, eventually with triangulation if intensities are present. The more wifi networks around, the higher is the accuracy of the positioning.
- adds additional networks you see that are currently not in the database to their database, so they can be reused later.
As you see, the system builds up by itself. The only thing you need is good seeding. After that, it extends in "50 meters chunks" (the range of a newly found wifi connection).
Of course, if you really want the system go banana, you can start exchanging wifi routers around the globe with fellow revolutionaries of the no-global-positioning movement.
回答2:
They use a combination of IP geolocation, as well as comparing the results of a scan for nearby wireless networks with a database on their side (which is built by collecting GPS coordinates alongside wifi scan data when Android phone users use their GPS)
回答3:
It's a lot more simple that you think. You've signed into both your mobile and Chrome on your desktop using the same Google account. Google simply expect you will have your mobile with you most of the time. They take the location data from your phone and assume the location of your current desktop session is the same.
I proved this by RDPing into my Windows machine at home from work and checking Google maps remotely. It show my location as the same as Chrome on Linux at work.
If you don't have a mobile that is signed into Google then all they can do is lookup GeoIP data for the IP address assigned by your ISP. It will typically be wildly inaccurate.
回答4:
I've finally worked it out. The biggest issue is how they managed to work out what Wireless networks were around me and how do they know where these networks are.
It "seems" to be something similar to this:
- skyhookwireless.com [or similar] Company has mapped the location of many wireless access points, i assume by similar means that google streetview went around and picked up all the photos.
- Using Google gears and my browser, we can report which wireless networks i see and have around me
- Compare these wireless points to their geolocation and triangulate my position.
Reference: Slashdot
回答5:
According to Google Maps' own help:
回答6:
Rejecting the WiFi networks idea!
Sorry folks... I don't see it. Using WiFi networks around you seems to be a highly inaccurate and ineffective method of collecting data. WiFi networks these days simply don't stay long in one place.
Think about it, the WiFi networks change every day. Not to mention MiFi and Adhoc networks which are "designed" to be mobile and travel with the users. Equipment breaks, network settings change, people move... Relying on "WiFi Networks" in your area seems highly inaccurate and in the end may not even offer a significant improvement in granularity over IP lookup.
I think the idea that iPhone users are "scanning and sending" the WiFi survey data back to google, and the wardriving, perhaps in conjunction with the Google Maps "Street View" mapping might seem like a very possible method of collecting this data however, in practicality, it does not work as a business model.
Oh and btw, I forgot to mention in my prior post... when I originally pulled my location the time I was pinpointed "precisely" on the map I was connecting to a router from my desktop over an ethernet connection. I don't have a WiFi card on my desktop.
So if that "nearby WiFi networks" theory was true... then I shouldn't have been able to pinpoint my location with such precision.
I'll call my ISP, SKyrim, and ask them as to whether they share their network topology to enable geolocation on their networks.
回答7:
I know you can look up IP address to get approximate location, but it's not always accurate. Perhaps they're using that?
update:
Typically, your browser uses information about the Wi-Fi access points around you to estimate your location. If no Wi-Fi access points are in range, or your computer doesn't have Wi-Fi, it may resort to using your computer's IP address to get an approximate location.
回答8:
It is possible get your approximate locate based on your IP address (wireless or fixed).
See for example hostip.info or maxmind which basically provide a mapping from IP address to geographical coordinates. The probably use many kinds of heuristics and datasources. This kind of system has probably enough accuracy to put you in right major city, in most cases.
Google probably uses somewhat similar approach in addition to WiFi tricks.
来源：https://stackoverflow.com/questions/1668304/how-does-google-calculate-my-location-on-a-desktop