Vehicle three-axis attitude determination method based on GNSS double antennas

Abstract

The invention relates to a vehicle three-axis attitude determination method based on GNSS double antennas, and belongs to the technical field of navigation methods and applications. The method comprises the following steps: measuring the value of a dual-antenna baseline vector in a vehicle coordinate system; obtaining the value of the dual-antenna baseline vector in a navigation coordinate system; acquiring the value of the speed vector of the vehicle in the navigation coordinate system; and performing dual-vector attitude determination by using the dual-antenna baseline vector and the vehicle speed vector under the navigation coordinate system and the vehicle coordinate system to obtain the three-axis attitude of the vehicle. According to the invention, three-axis attitude determination of the vehicle is realized based on the two GNSS antennas and the speed information of the forward state of the vehicle.

Description

Technical Field

[0001] The present invention belongs to the technical field of navigation methods and applications, and particularly relates to a vehicle three-axis attitude determination method based on GNSS dual antennas. Background Art

[0002] The integrated navigation technology composed of satellite navigation and inertial navigation is widely used in vehicle navigation and positioning. Before using the integrated navigation technology for vehicle positioning, it is necessary to obtain a relatively accurate vehicle attitude, including the pitch angle, roll angle, and heading angle of the vehicle. This process is also called initial alignment. As a key technology of the integrated navigation system, initial alignment has always been a research hotspot in vehicle navigation.

[0003] In traditional methods, the initial alignment of the vehicle is performed by using the speed information of the vehicle's forward state for dynamic alignment, or by using two GNSS antennas to obtain the vehicle attitude through baseline solution. However, both methods can only obtain the attitude information of two axes and lack the attitude observation of one axis (roll angle or pitch angle). Using three GNSS antennas can obtain the three-axis attitude of the vehicle, but the additional GNSS antenna undoubtedly increases the cost.

[0004] In view of the existing problems, the present invention proposes a vehicle three-axis attitude determination method based on GNSS dual antennas. Compared with traditional methods, this method realizes the three-axis attitude determination of the vehicle based on two GNSS antennas and the speed information of the vehicle's forward state, and has good application prospects in practical engineering. Summary of the Invention

[0005] (1) Technical Problems to be Solved

[0006] The technical problem to be solved by the present invention is how to provide a vehicle three-axis attitude determination method based on GNSS dual antennas to solve the problem that both existing methods can only obtain the attitude information of two axes and lack the attitude observation of one axis.

[0007] (2) Technical Solutions

[0008] To solve the above technical problems, the present invention proposes a vehicle three-axis attitude determination method based on GNSS dual antennas, and the method includes the following steps:

[0009] Step S1: Install the GNSS dual antennas on the top of the vehicle, the baseline vector formed by the dual antennas is perpendicular or close to the vehicle traveling direction, and measure the value of the dual antenna baseline vector in the vehicle coordinate system;

[0010] Step S2: Use carrier phase double-difference observations for baseline solution, or subtract the positioning results of two antennas to obtain the value of the dual-antenna baseline vector in the Earth-centered Earth-fixed (ECEF) coordinate system. Calculate the transformation matrix S between the ECEF coordinate system and the navigation coordinate system based on the GNSS positioning results, and obtain the value of the dual-antenna baseline vector in the navigation coordinate system;

[0011] Step S3: Start the vehicle to move forward. Use GNSS Doppler observations for speed measurement, or subtract the positioning results of two antennas at adjacent times to obtain the value of the vehicle's velocity vector in the ECEF coordinate system. Calculate the transformation matrix S between the ECEF coordinate system and the navigation coordinate system based on the GNSS positioning results, and obtain the value of the vehicle's velocity vector in the navigation coordinate system;

[0012] Step S4: Use the dual-antenna baseline vector and the vehicle's velocity vector in the navigation coordinate system and the vehicle coordinate system for dual-vector attitude determination to obtain the three-axis attitude of the vehicle.

[0013] (3) Beneficial effects

[0014] The present invention provides a method for three-axis attitude determination of a vehicle based on GNSS dual antennas. Compared with traditional methods, this method realizes the three-axis attitude determination of the vehicle based on the speed information of two GNSS antennas and the forward state of the vehicle, and has good application prospects in practical engineering. Description of the drawings

[0015] Figure 1 It is the time sequence diagram of the carrier attitude, speed and position of the present invention, as well as the projection of the motion trajectory on the XY plane of the local horizontal geographic coordinate system;

[0016] Figure 2 It is the three-axis attitude determination result of the carrier using GNSS dual antennas;

[0017] Figure 3 The flowchart of the method of the present invention. Detailed implementation manners

[0018] To make the objectives, contents and advantages of the present invention clearer, the following further describes the detailed implementation manners of the present invention in conjunction with the drawings and embodiments.

[0019] The present invention provides a method for three-axis attitude determination of a vehicle based on GNSS dual antennas.

[0020] The vehicle refers to a vehicle that conforms to the Ackermann motion equation;

[0021] The three axes refer to: roll angle, pitch angle, and heading angle;

[0022] The method for three-axis attitude determination of a vehicle based on GNSS dual antennas includes the following steps:

[0023] Step S1: Install the GNSS dual antennas on the top of the vehicle. The baseline vector formed by the dual antennas is perpendicular or close to the vehicle's traveling direction, and measure the value of the dual-antenna baseline vector in the vehicle coordinate system.

[0024] Step S2: Use the carrier-phase double-difference observations for baseline solution, or subtract the positioning results of the two antennas to obtain the value of the dual-antenna baseline vector in the Earth-centered Earth-fixed (ECEF) coordinate system. Calculate the transformation matrix S between the ECEF coordinate system and the navigation coordinate system based on the GNSS positioning results, and obtain the value of the dual-antenna baseline vector in the navigation coordinate system.

[0025] Step S3: Start the vehicle to move forward. Use the GNSS Doppler observations for velocity measurement, or subtract the positioning results of the two antennas at adjacent moments to obtain the value of the vehicle's velocity vector in the ECEF coordinate system. Calculate the transformation matrix S between the ECEF coordinate system and the navigation coordinate system based on the GNSS positioning results, and obtain the value of the vehicle's velocity vector in the navigation coordinate system.

[0026] Step S4: Use the dual-antenna baseline vector and the vehicle's velocity vector in the navigation coordinate system and the vehicle coordinate system for dual-vector attitude determination to obtain the three-axis attitude of the vehicle.

[0027] Preferably, the value of the dual-antenna baseline vector in Step S1 in the vehicle coordinate system is:

[0028]

[0029] where \(r_0\) represents the dual-antenna baseline vector, and the superscript \(v\) represents the projection in the vehicle coordinate system. The vehicle coordinate system is defined as the "right-front-up" coordinate system.

[0030] Preferably, the method for using the carrier-phase double-difference observations for baseline solution to obtain the value of the dual-antenna baseline vector in the ECEF coordinate system in Step S2 is:

[0031] Construct the station-satellite double-difference pseudorange observations and carrier-phase observations:

[0032]

[0033]

[0034] where represents the double-difference pseudorange observation formed by antennas \(i, j\) and satellites \(p, q\), represents the double-difference carrier-phase observation formed by antennas \(i, j\) and satellites \(p, q\) in units of weeks, \(\lambda\) is the carrier wavelength, is the double-difference Earth-satellite range, is the double-difference carrier-phase integer ambiguity, and are the double-difference pseudorange noise and the double-difference carrier phase noise.

[0035] Expanding the double-difference pseudorange observation and the double-difference carrier phase observation at the initial value of the projection of the baseline vector between the two antennas in the Earth-Centered Earth-Fixed (ECEF) coordinate system yields:

[0036]

[0037]

[0038]

[0039] where the subscript 0 represents the initial value, (l, m, n) are the direction cosines formed by the two antennas and the satellite, and dx e , dy e , dz e ) is the increment of the baseline in the ECEF coordinate system.

[0040] Using the double-difference pseudorange observation and the double-difference carrier phase observation to construct the least squares observation equation:

[0041] Z = HX + V

[0042]

[0043]

[0044]

[0045]

[0046] where Z is the observation vector, H is the coefficient matrix, X is the parameter to be estimated, V is the error vector, the superscripts 0 and 1 represent the reference satellite 0 and the rover satellite 1 respectively, and the subscripts i and j represent antenna i and antenna j respectively. V is the noise vector. The number of rover satellites is M + 1.

[0047] The weighted least squares estimation obtains the baseline solution result:

[0048]

[0049]

[0050] where is the estimated value of the parameter to be estimated, W is the weight matrix corresponding to the observation vector Z, is the projection of the baseline vector between the two antennas in the ECEF coordinate system.

[0051] The weight matrix W can be calculated through the satellite elevation angle and the differential relationship:

[0052]

[0053]

[0054]

[0055] Among them, σ pk and σ φk are the observation noises corresponding to the pseudorange and carrier phase observations of the k-th satellite respectively, and ele k is the elevation angle of the k-th satellite.

[0056] Preferably, the method for obtaining the value of the dual-antenna baseline vector in the Earth-centered Earth-fixed coordinate system by taking the difference between the positioning results of two antennas in step S2 is as follows:

[0057]

[0058] Among them, is the position of the right GNSS antenna in the Earth-centered Earth-fixed coordinate system when viewed from above the vehicle, is the position of the left GNSS antenna in the Earth-centered Earth-fixed coordinate system when viewed from above the vehicle.

[0059] Preferably, the calculation method of the transformation matrix between the Earth-centered Earth-fixed coordinate system and the navigation coordinate system in step S2 is as follows:

[0060]

[0061] Among them, lat and lon are the latitude and longitude of the vehicle respectively, which can be obtained from the positioning results of the GNSS receiver.

[0062] Preferably, the method for obtaining the value of the dual-antenna baseline vector in the navigation coordinate system in step S2 is as follows:

[0063]

[0064] Preferably, the method for measuring speed using GNSS Doppler observations in step S3 is as follows:

[0065] Construct the observations of the undifferenced Doppler frequency shift of each GNSS antenna:

[0066]

[0067] Among them, the superscript s represents the satellite; the subscript r represents the receiver; D is the Doppler frequency shift observation value; is the transmission frequency of satellite s; v s is the satellite speed; v r is the receiver speed; is the unit direction vector pointing from the receiver to the satellite, c is the speed of light; is the receiver clock drift; is the Doppler shift measurement noise.

[0068] Use the non-differenced Doppler shift observations to construct the observation equation:

[0069] Z = HX

[0070]

[0071] where v si is the velocity of the i-th satellite, (vx r , vy r , vz r ) is the receiver velocity vector in the Earth-Centered Earth-Fixed (ECEF) coordinate system. When the number of satellites is greater than 4, the velocity v of the antenna in the ECEF coordinate system is obtained by least squares estimation r .

[0072] Preferably, the method for calculating the vehicle speed using the positioning results of the GNSS antenna at adjacent times in step S3 is:

[0073]

[0074] where p r,k+1 is the positioning result of the GNSS antenna in the ECEF coordinate system at time k + 1; p r,k is the positioning result of the GNSS antenna in the ECEF coordinate system at time k; t k+1 -t k is the time interval between time k + 1 and time k; v r,k+0.5 represents the velocity of the GNSS antenna at the intermediate time between time k + 1 and time k.

[0075] Calculate the velocities v r and v r,k+0.5 results respectively, and take the average as the final vehicle velocity v e in the ECEF coordinate system.

[0076] Preferably, the method for calculating the vehicle speed in the navigation coordinate system in step S3 is:

[0077] v n = S · v e

[0078] where S is the transformation matrix between the ECEF coordinate system and the navigation coordinate system, and v e is the vehicle velocity in the ECEF coordinate system.

[0079] Preferably, the method for obtaining the vehicle's three-axis attitude by using the double-antenna baseline vector and the vehicle speed vector in step S4 is as follows:

[0080] When the vehicle is moving forward, the unit direction vector of the vehicle speed direction can be expressed in the vehicle coordinate system as:

[0081] v v =[0 1 0] T

[0082] Select the double-antenna baseline vector as the main vector, and perform orthogonal and unitization processing on the double-antenna baseline vector and the vehicle speed vector:

[0083]

[0084] Among them, and are two pairwise orthogonal unit vectors in the vehicle system; and are two pairwise orthogonal unit vectors in the navigation coordinate system.

[0085] Calculate the vehicle attitude matrix

[0086]

[0087] Calculate the pitch angle α, roll angle β, and heading angle γ of the vehicle:

[0088]

[0089] Among them, represents the element in the i-th row and j-th column of the matrix .

[0090] Example 1:

[0091] The experimental scenario of the present invention is an ordinary vehicle-mounted dynamic scenario, which is verified by simulation experiments. The starting point of the experimental trajectory is: geodetic latitude 40°, longitude 116°, and altitude 100m. The IMU sampling frequency is 100Hz. It is assumed that the IMU is installed inside the vehicle body and fixedly connected to the vehicle, the antenna is installed on the roof, and the lever arm error between the IMU center and the antenna phase center is set to 0. During the experiment, the initial speed of the vehicle is set to 0m / s, the maximum speed is 10m / s, and it includes turning and climbing and descending actions. The carrier attitude, speed, and position time series diagrams and the projection of the motion trajectory on the XY plane of the local horizontal geodetic coordinate system are as Figure 1 shown. Set the baseline solution accuracy to 0.005m and the speed measurement accuracy to 0.1m / s. Conduct experiments on the entire vehicle driving trajectory, and use the three-axis attitude determination accuracy as a measurement index to verify the feasibility and accuracy of this algorithm.

[0092] The experimental results are as follows:

[0093] Taking the attitude determination accuracy (RMS) as the measurement index. The experimental data from 10s to 50s when the vehicle speed is relatively fast are intercepted, and the results are as Figure 2 shown. After statistics, within this time period, the pitch angle accuracy calculated by this algorithm is 0.5764°, the roll angle accuracy is 0.2866°, and the heading angle accuracy is 0.2735°. This verifies the feasibility and accuracy of this algorithm.

[0094] The present invention proposes a vehicle three-axis attitude determination method based on GNSS dual antennas. Compared with the traditional method, this method realizes the three-axis attitude determination of the vehicle based on the speed information of two GNSS antennas and the forward state of the vehicle, and has good application prospects in practical engineering.

[0095] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can still be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. A vehicle three-axis attitude determination method based on GNSS dual antennas, characterized in that: The method comprises the following steps: Step S1, installing a GNSS dual antenna on the top of a vehicle, with the baseline vector formed by the dual antenna being perpendicular or close to the vehicle's traveling direction, and measuring the value of the dual antenna baseline vector in the vehicle coordinate system; Step S2: Use the carrier phase double difference observation value to perform baseline solution, or use the positioning results of the two antennas to make a difference, and obtain the value of the dual-antenna baseline vector in the geocentric earth-fixed coordinate system. Calculate the conversion matrix S between the geocentric earth-fixed coordinate system and the navigation coordinate system according to the GNSS positioning result, and obtain the value of the dual-antenna baseline vector in the navigation coordinate system; Step S3, start the vehicle to move forward, use GNSS Doppler observations to measure speed, or make a difference between the positioning results of the two antennas at adjacent times to obtain the value of the vehicle's velocity vector in the Earth-centered Earth-fixed coordinate system, calculate the conversion matrix S between the Earth-centered Earth-fixed coordinate system and the navigation coordinate system according to the GNSS positioning results, and obtain the value of the vehicle's velocity vector in the navigation coordinate system; Step S4: perform dual-vector attitude determination using the dual-antenna baseline vector and the vehicle velocity vector in the navigation coordinate system and the vehicle coordinate system to obtain the three-axis attitude of the vehicle.

2. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 1, characterized in that: The vehicle is a vehicle that conforms to the Ackerman equation of motion, and the three axes are roll angle, pitch angle, and heading angle.

3. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 1, characterized in that: In step S1, the value of the dual-antenna baseline vector in the vehicle coordinate system is: Wherein, r0 represents the dual-antenna baseline vector, the superscript v represents the projection in the vehicle coordinate system, and the vehicle coordinate system is defined as the "right front upper" coordinate system.

4. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 3, characterized in that: The step S2 of using the carrier phase double difference observation value to perform baseline solution to obtain the value of the dual-antenna baseline vector in the Earth-centered Earth-fixed coordinate system includes: Construct station-satellite double-difference pseudorange observations and carrier phase observations: in, represents the double-difference pseudo-range observation value formed by antenna i, j and satellite p, q, represents the double-difference carrier phase observation value in cycles formed by antenna i, j and satellite p, q, λ is the carrier wavelength, is the double differential ground-to-ground distance, is the double-difference carrier phase integer ambiguity, and is double difference pseudorange noise and double difference carrier phase noise; The initial projection value of the station-satellite double-difference pseudo-range observation value and the carrier phase observation value on the dual-antenna baseline vector in the Earth-centered Earth-fixed coordinate system Expand to get: Among them, the subscript 0 represents the initial value, (l,m,n) is the direction cosine formed by the dual antennas and the satellite, (dx e ,dy e ,dz e ) is the increment of the baseline in the Earth-centered Earth-fixed coordinate system; Using double-difference pseudorange observations and double-difference carrier phase observations Construct the least squares observation equation: Z=HX+V Where Z is the observation vector, H is the coefficient matrix, X is the parameter to be estimated, V is the error vector, superscript 0 and 1 represent reference satellite 0 and mobile satellite 1 respectively, subscript i and j represent antenna i and antenna j respectively; V is the noise vector; the number of mobile satellites is M+1; The baseline solution is obtained by weighted least squares estimation: in, is the estimated value of the parameter to be estimated, W is the weight matrix corresponding to the observation vector Z, is the projection of the dual-antenna baseline vector in the Earth-centered Earth-fixed coordinate system; The weight matrix W can be calculated through the satellite altitude angle and differential relationship: Among them, σ pk and σ φk are the observation noises corresponding to the pseudorange and carrier phase observations of the kth satellite, ele k is the altitude angle of the kth satellite.

5. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 3, characterized in that: The method for using the positioning results of the two antennas in step S2 to obtain the value of the dual-antenna baseline vector in the Earth-centered Earth-fixed coordinate system is: in, To see the position of the right GNSS antenna in the Earth-centered Earth-fixed coordinate system from above the vehicle, The position of the left GNSS antenna in the Earth-centered Earth-fixed coordinate system as viewed from above the vehicle.

6. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 4 or 5, characterized in that: The calculation method of the conversion matrix between the Earth-centered Earth-fixed coordinate system and the navigation coordinate system in step S2 is: Among them, lat and lon are the latitude and longitude of the vehicle, which can be obtained from the positioning results of the GNSS receiver; The method for obtaining the value of the dual-antenna baseline vector in the navigation coordinate system in step S2 is:

7. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 6, characterized in that: The method of using GNSS Doppler observation value to measure speed in step S3 is: Construct the undifferenced Doppler shift observations for each GNSS antenna: Wherein, the superscript s represents the satellite; the subscript r represents the receiver; D is the Doppler frequency shift observation value; is the transmission frequency of satellite s; v s is the satellite speed; v r is the receiver speed; is the unit direction vector from the receiver to the satellite, c is the speed of light; is the receiver clock drift; The noise is measured for the Doppler shift; Construct the observation equation using the undifferenced Doppler shift observations: Z=HX Among them, v si is the velocity of the ith satellite, (vx r ,vy r ,vz r ) is the receiver velocity vector in the Earth-centered Earth-fixed coordinate system; when the number of satellites is greater than 4, the antenna velocity v in the Earth-centered Earth-fixed coordinate system is obtained by least squares estimation r .

8. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 7, characterized in that: The method for calculating the vehicle speed by using the positioning results of the GNSS antenna at adjacent times to make a difference in step S3 is: Among them, p r,k+1 is the positioning result of the GNSS antenna in the Earth-centered Earth-fixed coordinate system at time k+1; p r,k is the positioning result of the GNSS antenna in the Earth-centered Earth-fixed coordinate system at time k; t k+1 -t k is the time interval between time k+1 and time k; v r,k+0.5 represents the velocity of the GNSS antenna at the intermediate moment between time k+1 and time k; Calculate the velocity v of the two GNSS antennas separately r and v r,k+0.5 The average of the results is taken as the final vehicle speed v in the Earth-centered Earth-fixed coordinate system e .

9. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 8, characterized in that: In step S3, the method for calculating the speed of the vehicle in the navigation coordinate system is: v n =S·v e Where S is the transformation matrix between the Earth-centered Earth-fixed coordinate system and the navigation coordinate system, v e is the speed of the vehicle in the Earth-centered, Earth-fixed coordinate system.

10. The vehicle three-axis attitude determination method based on GNSS dual antennas as claimed in claim 9, characterized in that: The step S4 comprises: When the vehicle is moving forward, the unit direction vector of the vehicle speed direction can be expressed in the vehicle coordinate system as: v v ＝[0 1 0] T Select the dual-antenna baseline vector as the main vector, and perform orthogonal and unitization processing on the dual-antenna baseline vector and the vehicle speed vector: in, and are the pairwise orthogonal unit vectors in the vehicle system; and are the pairwise orthogonal unit vectors in the navigation coordinate system; Calculate vehicle posture matrix Calculate the vehicle's pitch angle α, roll angle β, and heading angle γ: in, Representation Matrix The i-th row and j-th column element of .

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