Analysis of wireless positioning technology (1)

In fact, it is now the most popular Wi-Fi positioning. Its principle is similar to that of base station positioning:

1. Each Wireless AP has a unique MAC address in the world, and generally the Wireless AP will not move for a period of time.

2. when Wi-Fi is enabled, the device can scan and collect the peripheral AP signals, whether encrypted, connected, or even insufficient, and display them in the wireless signal list, can obtain the MAC address broadcast by the AP.

 

3. the device sends the data that can mark the AP to the location server, the server retrieves the geographical location of each AP, and calculates the geographical location of the device based on the strength of each signal, and returns the data to the User device.

4. The location service provider must constantly update and supplement their own databases to ensure data accuracy. After all, Wireless AP is not as basic as the base station tower and will not move 100%

 

Currently, there are only two location service providers, Skyhook and Google. They collect location data in a similar way.

1. Proactive acquisition: an important feature of Google's street scene shooting car is to collect wireless signals along the way, and attach the coordinates identified by GPS to the server;

Skyhook is also directly driving signal collection vehicles to collect signal data from AP and base stations in the United States and some European countries. It is not widely used in cities, but only a few cities in China are covered currently, they also recruited paid workers in multiple countries, including China, to help Skyhook collect location data. You can also directly submit a MAC address on your website.

 

 

In this way, positioning usually requires instant network interaction with the location server. Android is like this, and the best proof is that after the phone and GPS are disabled, when you enable Wifi but do not connect to any wireless network or connect to a network without access to the Internet, you cannot locate it. During the actual test, it is found that some software can still be located in this case, but no matter where the device is moved, the location in the application will never change. Because the Android API provides the LocationManager method. getLastKnownPosition: Android does not immediately locate the location data obtained in this way, but returns the last location data to the application, unless the application initiates a request to update the location.

However, Apple is incredible in terms of network interaction. A few days ago, I installed a map software on touch and downloaded an offline map. Because touch does not connect to WLAN, there is no other way to connect to the Internet. It is much easier to have an offline map. when I went out, I opened the map and found that touch accurately marked my location without any wireless network connection, after several steps, we found that the mark on the map was also accurately moved to the new coordinate. however, Google Map and some network software provided by the system cannot be located.

We know that we can locate through wireless, but how does Touch locate without network interaction?

At first, I guess that the offline map contains the location metadata. The map application collects Environment Information and calculates the location. The test is as follows:

Unmount the map application and reinstall it. After the installation is successful, the Wi-Fi connection is closed before it is enabled for the first time.) then, open the map application and locate the application. However, the map is not displayed.