CN106547002B - A kind of satellite selection method improving RTK positioning accuracy - Google Patents

Abstract

The invention discloses a satellite selection method for improving RTK positioning accuracy, and belongs to the field of RTK positioning of global satellite navigation systems. In the scheme of the present invention, after selecting a reference satellite according to the altitude angle, a double-difference residual threshold is set, the phase pseudo-range double-difference residual is calculated for the reference satellite and each ordinary satellite, and the satellite is selected according to its value. The solution of the invention has a small amount of calculation, and can dynamically adjust the threshold of the double-difference residual according to the different stages of the RTK positioning process, thereby accelerating the convergence speed of RTK positioning, and further improving the positioning accuracy of RTK. It is of great significance for applications that require increasing precision, such as detection.

Description

A Star Selection Method to Improve RTK Positioning Accuracy

technical field

The invention relates to the field of global satellite navigation system RTK positioning, in particular to a satellite selection method for improving RTK positioning accuracy.

Background technique

As an emerging technology, satellite global positioning system has been widely used in military, navigation and dispatching, geological exploration, surveying and mapping, development and other fields. Positioning includes single-point positioning and RTK (Real-Time Kinematic) positioning. In fields with high precision requirements such as geodetic surveying or engineering surveying, RTK positioning is usually used to ensure a certain accuracy.

Previous static, fast static, and dynamic measurements all required post-processing to obtain centimeter-level accuracy, while RTK can provide real-time three-dimensional positioning results of the station in the specified coordinate system, and achieve centimeter-level or even millimeter-level positioning accuracy. The first is the dynamic real-time differential method of carrier phase, which is a major milestone in the application. Its appearance brings a new dawn to engineering stakeout, topographic mapping, and various control measurements, which greatly improves the efficiency of field operations.

However, for dynamic real-time deformation monitoring such as landslide disasters, the effect of traditional RTK is not ideal, and the positioning accuracy of RTK needs to be further improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a star selection method for improving RTK positioning accuracy in view of the deficiencies of the prior art.

The technical solution adopted by the present invention to solve the technical problem is aimed at the situation that the baseline is short, and for each epoch, the following steps are included:

(1) If the number of visible satellites N is less than 4, the RTK positioning solution result of this epoch is no solution, and the next epoch is entered; otherwise, a satellite with the largest altitude angle is selected among all the visible satellites, As a reference satellite, the number is marked as 1;

(2) If the number of visible satellites N is equal to 4, skip step (2) and enter step (3), otherwise, calculate the phase pseudorange double-difference residual according to the following formula

Since i is the number of the reference satellite, the above formula can be embodied as:

in, is the difference between the phase pseudorange measurement value of the reference satellite received by the mobile station and the predicted distance; is the difference between the phase pseudorange measurement value of the reference satellite received by the base station and the real distance from the reference satellite to the base station; is the difference between the phase pseudorange measurement value of the ordinary satellite j received by the mobile station and the predicted distance; is the difference between the phase pseudorange measurement value of ordinary satellite j received by the base station and the real distance from ordinary satellite j to the base station; j=2,3,...,N; the predicted distance refers to: the result of RTK positioning solution to the satellite distance (at In the calculation, the satellite is the reference satellite; In the calculation, the satellite is the ordinary satellite j).

Judging which satellite needs to be eliminated according to the phase pseudorange double difference residual, the judgment method is as follows:

①For all j=2,3,…,N, satisfy:

V _L ^(1,j) > V _Thrd

Then it is considered that there is a problem with the reference satellite, the reference satellite is eliminated, and V _Thrd is the set threshold value, and returns to step (1);

② When ① is not satisfied, it is considered that there is a problem with ordinary satellites, and all ordinary satellites j that satisfy _VL ^(1,j) > V _Thrd are put into the set Del, and the value of _VL ^(1,j) increases from large to large. The small pair of satellite j is eliminated until N=4 or the set Del is empty.

(3) For the satellites retained after step (2), enter the normal RTK positioning solution link to realize satellite positioning.

In step (1) of the above technical solution, when the baseline is short, the altitude angles calculated using the base station or the mobile station are almost equal. Preferably, the base station is used to calculate the altitude angles of the satellites.

Preferably, RTK positioning is divided into four stages:

①Initial stage: before the fixed solution appears for six consecutive epochs;

②Initial->Stable stage: After the first fixed solution appears for six consecutive epochs;

③Stable -> Abnormal stage: After stage ②, due to the occurrence of abnormal conditions such as data quality deterioration, resulting in the appearance of floating-point solutions;

④ Anomaly -> Stable stage: after stage ③, after a fixed solution appears for three consecutive epochs;

The threshold V _Thrd is a dynamic value that satisfies the function:

Among them, t is the current epoch number, and t ₀ is the last epoch number that was stabilized by initial->stable or abnormal->stable. It can be seen that when the RTK positioning is in the initial, abnormal->stable stage, as the number of epochs increases, the value of V _Thrd will always decrease, but is always greater than 2.

Beneficial effects:

The star selection method provided by the solution of the present invention has a small amount of calculation, and can dynamically adjust the threshold of the double-difference residual according to the different stages of the RTK positioning process, thereby accelerating the convergence speed of RTK positioning and further improving The positioning accuracy of RTK is more obvious, especially for short baselines and poor observation environments.

Description of drawings

Figure 1: Schematic diagram of single difference

Figure 2: Flow chart of RTK star selection method

Figure 3: Algorithm simulation comparison diagram

Figure 4: Enlarged view of algorithm simulation comparison

Detailed ways

In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, and do not limit the protection scope of the present invention.

In conjunction with Fig. 2, a preferred embodiment of the present invention's method of selecting a star for improving RTK positioning accuracy is given: use the 24-hour IGS site jfng (China-Jiufeng) on January 1, 2016 as the base station (true coordinate Accuracy up to 2mm), wuh (China-Wuhan) as mobile station

(The accuracy of the true value coordinates reaches 3mm) for testing, the epoch interval is 30s, and the GNSS (Global Navigation Satellite System) system included in the data is only GPS (Global Position System). For the 720th epoch:

(1) The number of visible satellites in this epoch is N is 10, wherein, the altitude angle of No. 25 GPS satellite is the largest, which is 75°, as a reference satellite, the number is marked as 1;

(2) Calculate the phase pseudorange double difference residual according to the following formula

Since i is the number of the reference satellite, the above formula can be embodied as:

in, is the difference between the phase pseudorange measurement value of the reference satellite received by the mobile station and the predicted distance (the result of the positioning solution); is the difference between the phase pseudorange measurement value of the reference satellite received by the base station and the real distance from the reference satellite to the base station; is the difference between the phase pseudorange measurement value of the ordinary satellite j received by the mobile station and the predicted distance; is the difference between the phase pseudorange measurement value of ordinary satellite j received by the base station and the real distance from ordinary satellite j to the base station; j=2,3...,N; the predicted distance refers to: the result of RTK positioning solution to the satellite's distance distance (at In the calculation, the satellite is the reference satellite; In the calculation, the satellite is the ordinary satellite j).

After substituting the values, we get The values are: 1.5, 1.6, 2.2, 1.3, 2.9, 1.4, 0.8, 1.7, 0.6.

At this time, the RTK positioning is already in the initial->stable stage, and the epoch number of the last convergence is 220, and it is obtained that V _Thrd =2.368 at this time.

Determine which satellite needs to be eliminated according to the phase pseudorange double-difference residual:

① exist like Therefore, the reference satellite is retained and the next step is screened;

② Put the ordinary satellite j that satisfies V _L ^(1,j) >V _Thrd into the set Del, in this embodiment, the set elements are only The satellite j=6 can be eliminated.

(3) For the satellites retained after step (2), enter the normal RTK positioning solution link to realize satellite positioning.

In step (1) of the above technical solution, when the baseline is short, the altitude angles calculated using the base station or the mobile station are almost equal. Preferably, the base station is used to calculate the altitude angles of the satellites.

Principle description:

In the step (2) of above-mentioned technical scheme:

<1> Basis for star selection using double-difference residuals:

Single-difference observation equation (the following equation holds when the baseline is short):

Wherein, ri is the distance from the real position of satellite ⁱ to the predicted position of the mobile station; represents the direction from the satellite to the mobile station, (Δx, Δy, Δz) represents the deviation between the actual position of the mobile station and the predicted position of the mobile station, and ΔD _t is the difference between the clock errors of the mobile station and the base station.

Figure 1 depicts the relationship between single-difference observations.

in, is the actual distance between the satellite ⁱ and the base station, ri is the predicted position of the mobile station, is the true distance between the satellite i and the mobile station, are the phase pseudorange measurements of the mobile station and the base station, respectively (the wavy line in the figure represents the observation noise).

The proof of the above formula is given below in conjunction with Figure 1.

Prove: Since the errors in the ionosphere and troposphere of the base station and the mobile station are approximately equal, there are

in, is the clock difference of the mobile station; is the clock difference of the base station.

then:

That is, the above formula is established.

According to the single-difference observation equation, the double-difference observation equation is obtained:

because The three-dimensional accuracy of individual positioning (that is, the size of ||(Δx,Δy,Δz)||) is usually within 5-10m, and may reach more than 10m when the observation environment is harsh. Therefore, compared with The value of is more closely related to (Δx, Δy, Δz), which means that the deviation between the actual position of the mobile station and the predicted position can be judged by the double-difference residual to a certain extent. Therefore, selecting satellites based on the double-difference residuals of the phase pseudoranges can improve the positioning accuracy of RTK.

<2> Since the predicted position of the mobile station has a large deviation in the initial stage of positioning, if V _Thrd is set too small, some satellites will be mistakenly eliminated, which will affect the positioning performance.

Therefore, set V _Thrd to a dynamic value.

Preferably, RTK positioning is divided into four stages:

①Initial stage: before the fixed solution appears for six consecutive epochs;

②Initial->Stable stage: After the first fixed solution appears for six consecutive epochs;

③Stable -> Abnormal stage: After stage ②, due to the occurrence of abnormal conditions such as data quality deterioration, resulting in the appearance of floating-point solutions;

④ Anomaly -> Stable stage: after stage ③, after a fixed solution appears for three consecutive epochs;

The threshold V _Thrd satisfies the function:

Among them, t is the current epoch number, and t ₀ is the last epoch number that was stabilized by initial->stable or abnormal->stable. It can be seen that when the RTK positioning is in the initial, abnormal->stable stage, as the number of epochs increases, the value of V _Thrd will always decrease, but is always greater than 2.

The algorithm simulation is performed on the data used in this embodiment, and the results are shown in FIG. 3 and FIG. 4 .

It can be seen that the star selection method proposed by the present invention is very effective: in combination with Figure 3, the convergence time is 12 minutes earlier than the general RTK positioning algorithm; in combination with Figure 4, the final three-dimensional positioning accuracy of 24-hour data can be Reach 2mm, while the general RTK positioning algorithm is above 3mm.

The above-mentioned embodiment only expresses an optimal embodiment of the present invention, and its description is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can also be made, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims (3)

1. a kind of star selection method that improves RTK positioning accuracy, it is characterized in that what is aimed at is the situation of short baseline, for each epoch, all comprise the following steps: (1) If the number of visible satellites N is less than 4, the RTK positioning solution result of this epoch is no solution, and the next epoch is entered; otherwise, a satellite with the largest altitude angle is selected among all the visible satellites, As a reference satellite, the number is marked as 1; (2) If the number of visible satellites N is equal to 4, skip step (2) and enter step (3), otherwise, calculate the phase pseudorange double-difference residual according to the following formula Since i is the number of the reference satellite, the above formula can be embodied as: in, is the difference between the phase pseudorange measurement value of the reference satellite received by the mobile station and the predicted distance; is the difference between the phase pseudorange measurement value of the reference satellite received by the base station and the real distance from the reference satellite to the base station; is the difference between the phase pseudorange measurement value of the ordinary satellite j received by the mobile station and the predicted distance; is the difference between the phase pseudorange measurement value of ordinary satellite j received by the base station and the real distance from ordinary satellite j to the base station; j=2,3,...,N; the predicted distance refers to: the result of RTK positioning solution to the satellite the distance; Judging which satellite needs to be eliminated according to the phase pseudorange double difference residual, the judgment method is as follows: ①For all j=2,3,…,N, satisfy: V _L ^(1,j) > V _Thrd Then it is considered that there is a problem with the reference satellite, the reference satellite is eliminated, and V _Thrd is the set threshold value, and returns to step (1); ② When ① is not satisfied, it is considered that there is a problem with ordinary satellites, and all ordinary satellites j that satisfy _VL ^(1,j) > V _Thrd are put into the set Del, and the value of _VL ^(1,j) increases from large to large. The small pair of satellite j is eliminated until N=4 or the set Del is empty; (3) For the satellites retained after step (2), enter the normal RTK positioning solution link to realize satellite positioning. 2. a kind of star selection method improving RTK positioning accuracy according to claim 1 is characterized in that in step (1), use base station to calculate the altitude angle of satellite. 3. a kind of star selection method improving RTK positioning accuracy according to claim 1 is characterized in that RTK positioning is divided into four stages: ①Initial stage: before the fixed solution appears for six consecutive epochs; ②Initial->Stable stage: After the first fixed solution appears for six consecutive epochs; ③Stable -> Abnormal stage: After stage ②, due to the occurrence of abnormal conditions such as data quality deterioration, resulting in the appearance of floating-point solutions; ④ Anomaly -> Stable stage: after stage ③, after a fixed solution appears for three consecutive epochs; The threshold V _Thrd is a dynamic value that satisfies the function: Among them, t is the current epoch number, and t ₀ is the last epoch number that was stabilized by initial->stable, or abnormal->stable.