Principle behind Geolocation

LBS has been widely used in mobile devices and browsers. Based on APIs, it can easily implement address location-related applications, however, I still don't know how to obtain the user's location information behind these Apis. Today I spent some time studying it:

There are two ways to obtain location information: GPS and Wi-Fi.

1.
GPS

The basic principle of GPS is to measure the distance between the satellite at a known position and the receiver of the user. Then, the specific position of the receiver can be known based on the data of multiple satellites. To achieve this goal, the satellite location can be found in the satellite calendar based on the time recorded by the satellite clock. The distance from the user to the satellite is obtained by recording the time when the satellite signal is transmitted to the user's experience and multiplying it by the light speed. It can be seen that the function of GPS navigation system satellites is to continuously launch navigation messages. However, since the clock used by the user's receiver cannot always be synchronized with the satellite-mounted clock, in addition to the user's 3D coordinates x, y, and z,
Delta T refers to the time difference between the satellite and the receiver as an unknown number, and then the four unknown numbers are parsed using four equations. Therefore, if you want to know where the receiver is, you must be able to receive signals from at least four satellites.

As we can see from the above, GPS is not what I originally thought. The GPS device sends a request to the satellite, and the satellite returns the location.

The advantages and disadvantages of GPS positioning are as follows:

• Advantage: it is relatively accurate in an empty area and has a wide coverage.
• Disadvantages: it takes a long time to locate and consume battery resources. It is not good to work indoors and must be supported by GPS devices.

2. WiFi

Some geolocation service providers such as Google and skyhook will collect location information about Wi-Fi hotspots worldwide, then, if your device supports WiFi, you can obtain the location and signal strength information of the nearby Wi-Fi hotspot. Then, you can send the information to Google or skyhook to get your location. Among them, the most important thing is to collect the location information of Wi-Fi hotspots. There are two methods. One is that providers (such as Google) drive to collect data from around the world, as shown in:

City streets:

Tricycle:

Indoor:

The other is to provide location information through user input by the user's device or manually.

Browsers are located based on WiFi, but the providers used are different:

Firefox & grome: Google

Safari: skyhook

The advantages and disadvantages of WiFi are as follows:

• Advantage: relatively accurate, suitable for indoor environments, and fast
• Disadvantage: not applicable in areas with few Wi-Fi hotspots

There are other positioning methods:

3. IP

The IP address location principle is very simple, that is, it is located through the address information recorded by the physical address of your device, but this method is difficult to be accurate, especially when the Internet is connected Based on proxy, generally, it is roughly Fuzzy Matching When GPS and Wi-Fi are not supported, such as the cities where major group buying websites detect users.

4. Mobile phone Base Stations

Similar to the WiFi principle, the Wi-Fi hotspot is replaced by the base station. In fact, Apple's device is to combine the WiFi and the base station information for positioning.