IOS positioning principles and usage suggestions

I have seen many netizens discuss the positioning of iOS devices. Here I will give a detailed introduction to the positioning principles of iPhone, iPad, and iPod, hoping to increase the knowledge and reduce misunderstandings, make better use of iOS devices.

Before introducing this article, I first declare the "offset correction" function for map addition. Map addition can align the coordinates of the China Region (location, line, and photo) and the China map, this is a mathematical offset required by China's surveying and mapping regulations. The offset of each place is fixed and legal, and has nothing to do with the current positioning method, positioning accuracy and accuracy. That is to say, adding only alignment offsets on the map does not increase, decrease, or change the speed, accuracy, and rules of iOS positioning, nor does any App allow or allow the operations.

All the following descriptions of positioning errors, positioning offsets, and positioning accuracy are for iOS positioning hardware and are irrelevant to map addition or any app, it is also suitable for the positioning logic of all map apps on iOS, including the map App that comes with Apple.

The content is very long, but given that typing is harder than viewing posts, you will be considerate and have the courage to read it slowly. (For details, please refer to the source and second cool-map and add official forums and URLs .)

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Which methods can be used to locate iOS devices?

The earliest iPhone only supportsMobile phone base station positioningAnd then introduced through the iOS software upgradeWIFI PositioningSince the iPhone 3G, the iPhone uses the built-in GPS processing chip to supportGPS satellite positioning(To be precise, it should be AGPS, that is, auxiliary GPS ). since iPhone 4, GPS has switched to chips with higher precision, less power consumption, and higher sensitivity. Since iPhone 4S and new iPad 3G, GPS has increased support for Russia.GLONASSSupport for satellite positioning systems.

The following lists in detail all devices and positions supported:

There are three positioning modes:

1. Satellite Positioning

(1) GPS satellite positioning: iPhone 3G/3GS/4/5, 3G/4G iPad support

(2) GLONASS Satellite Positioning: supported by iPhone 4/5, 3G/4G iPad 3/4/Mini

2. Mobile phone base station positioning

The same as 1.1GPS satellite positioning, that is, iPhone 3G/3GS/4/5 3G/4G iPad support

3. WIFI Positioning

All iOS devices, including Mac computers, are also supported.

The following describes the three positioning methods and Apple's optimization in iOS systems:

Mobile phone base station positioning:

Principle:

Each mobile phone base station has an identifier. The iPhone or 3G iPad can collect all the base stations that receive signals and their identifiers and send them to the Apple cloud server over the Internet, the server then queries and calculates the current location based on the location information of these base stations, and then returns it to the mobile phone. Because the base station signal radiation range is large, the error is also large, ranging from 500 meters ~ Several kilometers.

Features: the fastest positioning speed, the least power consumption, and hundreds of kilometers of error.

IOS optimization:

No network base station positioning:

Traditional base station positioning requires connecting to the cloud server to generate network traffic. iOS 4 has optimized it to support non-network location when there is no network connection, because Apple has already stored some important base stations (several dozen kilometers) in the iOS system in advance. Without a network connection, the local base station information can be used to locate the user's location without having to access the Internet, however, this error range is greater, ranging from 10 km to 50 km.

The premise of positioning a no-network base station is that your mobile phone can receive the "Important Base Station" Signals embedded in your mobile phone, not necessarily the carrier of your mobile phone, as long as you can receive the signal.

Base Stations supported by iOS 4 with no network connection locations worldwide:

WIFI positioning:

Principle

Similar to the base station positioning principle, iOS devices (or Mac computers) use all WIFI hotspots around the wireless network card mobile phone (no need to connect, just need to have a signal ), obtain their MAC addresses, and then go to the Apple cloud server to check whether the hotspot has been registered. Then, the location of the hotspot is registered and finally calculated (multiple hotspots compromise) obtain the current location and return it to the user. As long as the location where the phone signal is received can be located by the base station, the indoor and outdoor environments are the same.

Features: The positioning speed, power consumption, and precision of WIFI are between the base station and GPS, and the precision is about dozens of meters. (Note: The support scope for WIFI positioning is not widely located by the base station, but Apple's cloud servers are constantly adding new hotspot information, increasing the number of regions supported by hotspot positioning)

All regions that support WIFI in iOS 4:

IOS optimization:

No network WIFI positioning:

Traditional Wi-Fi positioning requires a network, but iOS has optimized it to achieve no-network WIFI positioning. When the iOS device has a network connection, it will roughly locate you and automatically download the surrounding area (several blocks in width or more) all WIFI Hotspot information is sent to the local device. Then, when you are walking around and positioning by WIFI, even if there is no network, iOS can still use the previously downloaded WIFI Hotspot information to locate your location.

This is also why some people claim that WIFI is uncertain, but note: the premise of No-network WIFI positioning is that you have successfully accessed the network in the vicinity of this area. If you first arrived in a strange place, it cannot be located.

The number and range of automatically downloaded hot spots are determined by Apple Based on the density of local hot spots. When there are many local hot spots (such as the city center ), you may only download all the hot spots in several sub-district ranges. The local hotspot density is very small (such as the coastal city), and all the hot spots in the whole city may be downloaded.

It is an approximate scope for iOS to automatically download nearby Hotspot information in high-density areas:

GPS positioning:

(The GLONASS principle is similar to this. We will not introduce it any more)

Principle

This is done by the US military and is dual-purpose, but still completely controlled by the military (for example, you can set the signal received in a region anytime and anywhere). The principle is: the sky's satellites (24 in total) are used to continuously broadcast signals. After GPS receiving devices on the ground receive signals, by analyzing multiple satellite signals, the Earth coordinates can be calculated, GPS ensures that at least four satellite signals can be received at the same time in any part of the world (98%), so that you can accurately determine your longitude and latitude and altitude. GPS positioning accuracy can be up to 10 meters, but this is controlled by the US military. It may become unstable or false positive during war. (However, China also has its own system, which is currently covered in Asia and is still being promoted)

Satellite Positioning must be able to receive satellite signals, because the satellite signals are very weak. Although the iPhone 4 started to improve the sensitivity of the GPS hardware, it still needs to be used by the window or outdoors, in order to ensure the strength and stability of satellite signals.

Compared with base station positioning and WIFI positioning, GPS has the largest power consumption, the slowest speed, but the highest accuracy.

The iPhone GPS and pure GPS positioning is different, called A-GPS, that is, auxiliary GPS. (better than GPS, but GPS is also divided into chips and performance, not to say that all AGPS are better than all GPS)

Because GPS positioning is the most time-consuming and consumes the most power, it may take tens of seconds or even minutes to obtain information about satellites in the sky, which are visible, at what position, and what the clock is, AGPS uses the network. First, it sends the approximate location obtained from the location of the base station or Wi-Fi to a remote server, where the server queries and computes the current satellite information at this location, if the information is fed back to the iOS device, the iOS device can directly use the information to receive satellite signals without scanning and analyzing it by itself. This greatly improves the positioning speed and shortens the initial positioning time to 1 ~ Completed in 2 seconds.

The advantage of A-GPS is fast positioning, the disadvantage is that the network is needed, but it is only needed for the first time positioning, because once the satellite information is returned, in a limited time and scope, the information does not need to be changed, in the future, GPS positioning will no longer need to connect to the Internet. These satellite parameters are used directly to receive information.

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On iOS devices, the above Positioning method will be applied comprehensively. Generally, a location may be returned Based on the fastest "no-network base station location". When there is a network connection, use a network base station to locate and update the location, and then use AGPS to query the satellite star map. Finally, use GPS Positioning when the GPS signal is received.

Based on the current signal situation and network environment, iOS may iterate over and over the above methods, not necessarily consistent with the specific steps or methods. As iOS upgrades, the positioning sequence and rules may change.

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FAQs:

1. Why is the current positioning error of my iPhone several hundred or kilometers above?

The initial positioning of the iPhone is based on a base station or no-network base station, with an error of several hundred or several kilometers. Then, if you cannot find the Wi-Fi signal or the satellite signal, it will always be this precision.

You can enable the WIFI function (you don't need to connect to it, you just need to open it), or to the side of the window, or outdoors to receive satellite signals;

Solution: Wait for a while to enable the data traffic (close after locating) or go outdoors.

2. Why is my position always changed?

According to the current network environment, iOS will constantly adjust and revise the positioning method. The base station and Wi-Fi signal in your region may be too complex or too weak, for example, connecting the base station and connecting the other base station later, this results in unstable iOS computing locations.

Solution: Enable the WIFI function, enable data traffic (close after locating), or go outdoors.

3. Can I locate the problem without a mobile phone signal? Can I locate data-free traffic?

For iPhone or 3G/4G iPad

Scenario 1: [no mobile phone signal, no WIFI signal, no Internet access] positioning can only be performed outdoors using GPS. The initial positioning time may be long, it may take several minutes, and then the positioning will be normal.

Scenario 2: [no cell phone signal, WIFI signal, no Internet connection] If you have previously accessed the Internet and downloaded a nearby hotspot, you can locate the location using no network WIFI. Otherwise, same as Case 1.

Case 3: [no cell phone signal, Wi-Fi signal, and Internet access] locate the location using WIFI, and download a large number of WIFI hotspots in a large area, it is used to locate the problem of No-network WIFI in the future.

Scenario 4: [mobile phone signals, Wi-Fi signals, and no Internet access] If you receive signals from iOS's built-in "Important Base Stations", you can use these base stations to locate hopeless base stations. Otherwise, unable to locate.

Case 5: [mobile phone signal and Wi-Fi signal are not available, you can access the Internet] use the base station to locate the network, and the local "Important Base Station" information may be updated.

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For iPad WIFI:

Case 1: [No Wi-Fi signal, no Internet access] cannot be located

Case 2: [WIFI signal, no Internet access] If you have been on the Internet before, you can locate the location using no Internet WIFI. Otherwise, you cannot locate the location.

Case 3: [With WIFI signal, you can access the Internet] Use WIFI to locate and download all WIFI Hotspot information in a large area, which will be used for no-network WIFI location in the future.