Which iPad-WIFI edition can be accurately located without 3G modules?

Which iPad-WIFI edition can be accurately located without 3G modules? (2012-04-17

I often ask this question: why can I locate the iPad-WIFI without 3G modules? It takes about two seconds to use the IPHONE to locate the device, and the street in which the device is located immediately flashes in the center of the screen. No wonder Steve Jobs also said: "It's
Really
Cool ", this function is amazing. In the past, base station positioning and GPS positioning were either long or the error could be as large as a kilometer, while the iPhone's center was located several dozen meters away from me.

To solve this problem, we must understand the positioning principles of iPad and iPhone. First, how did I locate the iPhone? I will explain that there are three ways for iPhone to communicate and locate, namely GPS, Carrier Base Station, and Wi-Fi hotspot. Let's take a look.

* GPS: GPS is an English Global Positioning
System (global positioning System. GPS is a global satellite navigation and positioning system developed by the US military. It consists of 24 satellites. More than three satellites can be seen at any point in time in any part of the world. The main feature of GPS positioning is that it is truly unique in the world, and the positioning accuracy can reach a maximum of 1-5 meters. The disadvantage is that it must be able to receive satellite signals outdoors for a long time.

* Carrier Base Station: The Carrier Base Station Information has its unique code, so it can be quickly located at an approximate location of 1-5 kilometers. The advantage is that it can be located either outdoors or indoors wherever there is a carrier base station.

* WIFI Hotspots: WIFI itself does not provide positioning capabilities, but the three features of WIFI are: one is that WIFI hotspots are rarely moved, and the other is that all WIFI will have a unique globally-MAC address.

The iPhone of each of us is actually the Information Collector of the Apple map system. When we are outdoors, the mobile phone will send the MAC address, GPS location information, and Carrier Base Station Code of the Wi-Fi you have collected to the Apple server at the same time. The server knows the exact geographic location of the router. In the future, devices without GPS can use the MAC address of this vro for locating.

Someone asked? If I do not have a connection to WIFI, will I not be able to get location information? The answer is no. The reason is that when the iPhone is looking for a Wi-Fi SSID, it will be able to get the MAC address of the WIFI. That is to say, WIFI provides a location tag for the iPhone for free, whether or not it is connected to the WIFI. That is, the MAC address of the Wi-Fi can be obtained even if the Wi-Fi is not connected.

Some guys also want to ask, why can we locate in the office, but at the door of the office building? This is also a good problem, and the reason is simple. Apple's map system has a set of algorithms, such as walking on the way to work, entering office buildings, and connecting to the WIFI in your office, and your base station information indicates that you are not far away, and there are many users with the same behavior as you, so the server thinks that the Wi-Fi in your office is located at the door of your office.

Although our iPad (WIFI version) does not have 3G modules, that is, it does not have Carrier Base Station information, but it can be precisely located, the principle is that when the iPhone is connected to the Internet, the corresponding environment information (the MAC address of WIFI) is sent to the server. Each iPad only needs to be able to access the Internet and send the MAC address of WIFI to the server in the background, the server will naturally be able to reflect the exact location of the current WIFI. That is why no 3G module is available for iPad-WIFI.

Apple actually uses the technology of Skyhook, which seems to have recently filed a patent lawsuit against Google. Although this technology is restricted by the scope of service and has no data such as direction and speed, it cannot be used for navigation or offline. However, it has a better advantage than GPS, that is, where the population and buildings are more intensive, the better the use effect. GPS has been started for a long time. It is ineffective in the room. When the weather is bad, the performance is poor, and the buildings are too dense. These factors have been overcome by WIFI positioning.

In addition, there are several sp about GPS: 1. GPS is very accurate, but because there is a mysterious "related department" in China, the map must have an offset in the administration. This may cause GPS and map location deviations. 2. the information sent by the GPS satellite to the mobile phone is transmitted individually. The GPS only transmits the current accurate time to the user. The user uses the time difference of several satellites to calculate the current position. 3. Because of the need for high precision, GPS will use a magical theory of relativity to correct location deviations. 4. GPS can be positioned when three stars are working, and when four stars are located, the altitude can be located (love of mountain climbers)