GPS precision factor (GDOP, pdop, hdop, vdop, tdop)

 

Pdop: Position dilution of precision. It is translated as "precision intensity" and is usually translated as "relative error ". The specific meaning is: because the quality of the observed results is related to the geometric shape between the measured man-made satellite and the receiver, therefore, calculating the error volume caused by the above is called the strength of accuracy. The better the satellite distribution in the sky, the higher the positioning accuracy (smaller the value ).Pdop is a parameter that represents the relationship between the positioning accuracy of a 3D position and the geometric configuration of the navigator. In the global positioning (GPS) system, the ratio of the radial error (1 °) equal to the measurement error (1 °) from the user to the satellite.

The pdop value range is 0.5 -- 99.9, which is the root number of the sum of squares of errors, such as latitude, longitude, and elevation. Therefore, the square of pdop = the square of hdop + the square of vdop.

In ry, pdop is divided equally by the volume ratio of the cone consisting of the receiver and the lines of the four satellites that can be observed. For good positioning, the pdop value is small, for example, 3. It is considered to be worse than 7 values. Therefore, small pdop values are related to distant satellites.

In GPS navigation and positioning, we use the geometric accuracy factor (DOP, dilution of precision) to measure the influence of the spatial geometric distribution of the observed satellite on the positioning accuracy. DOP is divided into the following types:
Position dilution of precision (pdop) three-dimensional position precision factor: it is the root number of the sum of squared errors, such as latitude, longitude, and elevation.
Tdop (time dilution of precision) accuracy factor: it is the offset error value of the table in the receiver.

Hdop (Horizontal dilution of precision) horizontal component precision factor: it is the root number of the sum of squares of errors such as latitude and longitude.
Vdop (vertical dilution of precision) vertical component precision factor
The DOP value is proportional to the GPS positioning error. The larger the DOP value, the larger the positioning error, and the lower the positioning accuracy. Pdop directly reflects the distribution of GPS satellites. When pdop is large, it indicates that the geometric distribution of the Four GPS satellites in the air is not ideal, and their graph perimeter is too short, low positioning accuracy, and vice versa.

The precision attenuation factor (DOP) is an indicator of the position quality. It is the calculation result of predicting the location accuracy of each satellite relative to other satellites in the constellation (geometric location. A small DOP value indicates a high probability of satellite geometric position and accuracy. A high DOP value indicates a low probability of weak satellite geometric positions and precision.
A gps receiver can get a lot of satellite positioning information at the same time, but in precision positioning, as long as four satellite signals are enough, A good receiver can determine how to extract reliable signals from these satellite signals for computation. If two satellites are very close to the signals selected by the receiver, two satellite signals are generated in an overlapping area in a relatively small angle. The closer the distance, the larger the area, and the larger the error affecting the accuracy. If the selected satellite is separated by a distance, the signal intersection is clearer, and the error is certainly reduced.

This also shows from another aspect that, although the satellite signal on the top of our head is relatively good and relatively easy to lock, their functions are actually inferior to those of satellites with relatively low angle.

The simple relationship between them is:

Hdop2+ Vdop2= Pdop2

Pdop2+ Tdop2= GDOP2 

Geometric Dilution precision (GDOP) is an important factor for measuring positioning accuracy, it represents the distance vector amplification factor between the receiver and the spatial satellite caused by GPS ranging error. The actual representation of the physical volume outlined by the unit vector from the receiver to the space satellite involved in the Positioning Solution is inversely proportional to GDOP, so it is also known as the geometric accuracy factor.

In fact, the larger the value of GDOP, the smaller the volume of the Unit vector, that is, the result of the very similar angle between the receiver and the spatial satellite. At this time, GDOP will cause the positioning accuracy to deteriorate. A good GDOP refers to a small value that represents a large unit vector volume, resulting in a high positioning accuracy. A good geometric factor actually means that satellites are not concentrated in one region and can be evenly distributed across different regions.