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All You Need to Know about High Accuracy GPS Tracker
Jimi loTJimi loT2019-10-09
How accurate is GPS tracker?
GPS locator is used for tracking vehicles and anti-theft. When purchasing a GPS tracker, the most important thing people care about is accuracy. The accuracy of the GPS tracker determines the error of the actual positioning. Then, how accurate is GPS tracker? GPS tracking devices are usually using a GPS positioning system with an accuracy of 0.3 m. However, the positioning accuracy of 0.3m can only be applied to the military, in the open civilian application, and the accuracy of the GPS global satellite system is 3m. 
Does this mean that the highest accuracy of the GPS tracking unit is 3m? Yes. However, this is in an ideal state. In other word, the GPS tracker is placed in the open space, the weather is particularly good and the GPS signal is perfectly strong, only 3m error will occur in this condition.
In fact, many factors such as weather, building, etc. are affecting the positioning accuracy of the GPS positioner. Therefore, the GPS tracker cannot achieve 3m accuracy generally.

So what is the actual maximum precision that the GPS tracking can achieve? It is about 10m.

GPS positioning accuracy is determined by many factors
What is the cause of GPS position drift and position deviation? Under what circumstances can such phenomena be avoided? Let's analyze the reasons one by one.
Before analyzing GPS positioning drift, we first need to understand how GPS realizes positioning based on satellite signals. GPS (Global Positioning System) includes three major parts: space GPS satellite constellation, ground monitoring system and user GPS signal receiver. The basic principle of GPS positioning is: satellite constantly launch its own ephemeris parameters and time information, GPS unit receives signals, and then according to triangle formula, GPS receiver can get its position. Three satellites for 2D position (latitude and longitude), four satellite can realize 3D positionings (longitude, latitude and altitude). By constantly updating the receiver information, the direction and speed of movement can be calculated. At present, there are 24 GPS navigation satellites distributed in 6 orbits, and at any time there are at least 4 satellites and at most 11 satellites above the horizontal line, so GPS positioning can be well guaranteed. As a GPS signal receiving terminal, the navigator functions to capture satellite signals, amplify and process the signals, and calculate the 3D position and speed of the receiver in real time.

What factors will affect the positioning accuracy? Let's start with external conditions.
1. Atmosphere (specifically the delay of the ionosphere and troposphere to GPS signals)
The ionospheric delay is caused by the refraction effect of the ionosphere around the earth on electromagnetic waves, which causes the propagation speed of the GPS signal to change. This change is called the ionospheric delay. Tropospheric delay refers to the refracting effect of the troposphere around the earth on electromagnetic waves, which causes the propagation speed of the GPS signal to change. This change is called tropospheric delay.
2. Satellite clock error
Even if the satellite is very sophisticated, it can calculate some very small information, such as the Cesium is such a precise device, but accuracy does not mean perfect, there will still be some minor errors, even the positioning of the satellite continues to be monitored, but not every second is in the state of being monitored. During this period, if there is a slight positioning error or satellite ephemeris error, it will affect the receiver in the accuracy of the positioning calculation.
3. Ephemeris error (i.e. satellite orbit error)
During GPS positioning, the parameters of satellite orbit needed to calculate the position of GPS satellite at a certain moment are provided by various types of ephemeris. However, no matter which type of ephemeris is used, the calculated satellite position will be different from its real position, which is called ephemeris error.

In addition, there are external factors with variability, such as the number of visible satellites and the distribution of satellites, which also have a significant impact on the positioning accuracy of GPS receiving terminal.
In addition to the external conditions that affect the GPS positioning accuracy that we just introduced to you, there are also many human factors that also affect the precise positioning of the receiving terminal.
1. Multipath effect (GPS signal reflected by other surfaces into the receiver antenna)
Due to the influence of the environment around the receiving terminal, the multipath effect causes the received satellite signal to also contain the influence of reflected and refracted signals. This is called multipath effect. For example, in high-rise buildings and mountain jungles, the probability of satellite signals being reflected or refracted is quite large.
2.SA policy
The SA policy is a method for the US government to reduce the accuracy of broadcasting ephemeris accuracy (technology) and adding high-frequency jitter to GPS signals to reduce accuracy. The ordinary GPS signal has two codes, which are C/A code and P code. The error of the C/A code is 29.3m to 2.93 meters. A typical receiver calculates the position using a C/A code. In the mid-1990s, for the sake of its own security, the United States added SA (Selective Availability) to the signal, which increased the error of the receiver to about 100 meters. On May 2, 2000, SA was canceled, so our current GPS accuracy should be within 20 meters. The P code error is 2.93 meters to 0.293 meters, which is one-tenth of the C/A code, but the P code can only be used by the US military.
3. Human interference factors
The GPS control part is artificially affected, due to problems in the GPS control part or errors introduced by the user when performing data processing, or the impact of computing data processing software, the impact of the data processing software's imperfect algorithms on the positioning results. That is to say, while the map program is started, the navigation device performs other data processing, which causes data errors and affects the accuracy of GPS positioning.

Others, such as electromagnetic pulse interference in the car and other electronic products in the car have more or less impact on GPS positioning, but these effects are controllable.The environment of the receiving terminal also has a great influence on the positioning accuracy.

What we can do for high accuracy GPS tracker?
when using GPS tracker:
1. After launching the positioning terminal, the satellite search should be conducted as far as possible in the area with open terrain, rather than in the blind area of satellite signals such as high buildings or basement. In the satellite search stage, the terminal should be provided with a good satellite reception range for accurate positioning.
2. In case of frequent star loss or signal drift, the receiving terminal can be equipped with an external antenna to obtain a better satellite signal reception effect.
3. Don't blindly believe the start time of the navigator. No matter how good the satellite receiving module is, it can't make accurate positioning without good satellite signals.

when purchasing GPS tracker:
At present, there are many cheap GPS trackers on the market that use low-end chips for positioning. One of the advantages of using low-end chips is that they are low price, but the defects are also very obvious. The positioning in the open areas is usually more accurate and the deviation is not large. However, in the city or in the complicated terrain, the disadvantages are highlighted, and the deviation will be relatively large, reaching more than 100 meters or even hundreds of meters. So what we can do when purchasing a highly accurate GPS tracker?
When you want to purchase trackers, you can't just look at the price and official propaganda, but also look at which chip is used by the manufacturer. The chip is the central hub of the GPS tracker. The current mainstream GPS chips are as follows.
At present, most GPS chip of GPS module adopts SiRFIII series, which ranks first in the global market share. Globalsat and RoyalTek GPS modules are both based on Sirf Star III. 
MTK is a newcomer, but it is growing fast. MTK II chipset has 66 channels, the most GPS channels in the market have the best overall performance.
Ublox works reliably and performs well. It can pick up GPS signals very quickly no matter the vehicle is moving or stationary. GPS signal acquisition is also best if the vehicle comes out of the tunnel. Also, it is better in craftsmanship and appearance.
So,check GPS chip twice before purchasing GPS tracker.

To sum up, GPS positioning accuracy is not only derived from the receiving terminal itself. There are many immutable external factors that affect GPS receiving satellite signals at all times, thus causing GPS positioning deviation. Therefore, when we use GPS to guide ourselves, we try to avoid the influence of human factors on the receiving terminal itself, and give GPS a good use environment to the greatest extent, so that it can reflect the advantages of positioning and navigation.

Of course, high accuracy is not the only element you should purchase or use a GPS tracker. Jimi IoT is in GPS industrial for years, welcome to contact us if you want to know more.

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