We know that the satellites are in the right orbit. The correct trajectory is programmed into an ephemeris, injected into the satellite, and sent to the GPS locator via satellite. By correctly receiving the ephemeris of each satellite, the exact position of the satellite can be ascertained.
The GPS system has a very precise atomic clock on each satellite and is constantly calibrated by the monitoring station. The satellite sends navigation information and also sends precise time information. The GPS locator receives this information and synchronizes it with its own clock to get the exact time. Therefore, in addition to accurate positioning, GPS locators can generate accurate time information.
Since the position of the satellite is accurate, in the GPS observation, we can get the distance from the satellite to the receiver. Using the distance formula in the three-dimensional coordinates, using three satellites, we can form three equations and solve the position of the observation point (X , Y, Z). Considering the error between the satellite clock and the receiver clock, there are actually four unknowns, X, Y, Z and clock difference. Therefore, it is necessary to introduce the fourth satellite to form four equations to solve the problem. Latitude and longitude and elevation.
It can be known from the principle of GPS usage that the GPS locator does not transmit signals, and it only receives satellite transmission data for calculation to solve the positioning problem. However, if you are in the high-rise areas of the city, you often face a small number of search stars. In the actual use process, the general situation of the three stars can basically be initially positioned, as shown below. From this, the lateral coordinate, the longitudinal coordinate and the height can be determined.
However, in the high-rise areas of the city, there are high-rise buildings around, and the GPS locator is in a weak signal, so the direct capture may be only one star or two stars on the top of the head. If you adjust the GPS positioner, you can often accept three stars or even four stars. At this time, some of the signals received are often reflected by the satellite.
As shown in the following figure, the 3rd star is blocked by the high-rise building. The red line is the direct ray without blocking. At this time, it is blocked by the high-rise building, and the GPS signal is not received. At this time, the signal reflected by the 3rd star through the high-rise building appears in the GPS locator.
According to the calculation formula, the receiver determines its position based on the distance from which the stars 1, 2, and 3 are obtained. We assume that if there is no star 3, the result of the operation: the position reflected by the stars 1 and 2 can only be positioned on an arc, as shown by the orange line in the figure.
The reflected signal received by the star 3 forms an incorrect distance length in the GPS locator, and the length of the blue polyline in the figure. If the length is the radius (shown by the green line) and the star 3 is the center of the circle, we can draw a sphere. The sphere (shown by the yellow line) intersects the orange line is the position judged by the receiver (red star position). Of course, this position is subject to error.
In summary, in urban high-rise areas, especially when GPS tracker satellite signals are blocked, such as in windows, basement ports, garage doors, etc., it is easy to drift.
GPS locator consumes fast power
We know that when the phone turns on the GPS function, it consumes a lot of power. The same is true for the GPS locator. When the GPS is in constant working state, the power will lose very fast. This is because the device is constantly receiving and transmitting data, and this process consumes a lot of power. If you want a long standby time GPS locator you can choose AT-2 and TR21 from Huizhou Great-Will Industrial CO., Ltd. Both are ultra long standby 2 year wireless locators.