Multi-GNSS fusion positioning method and system

Abstract

The invention relates to the technical field of information processing, and particularly discloses a multi-GNSS fusion positioning method and system, and the method comprises the steps: determining an available GNSS signal according to the real-time performance of the GNSS signal, a status bit signal and the spatial continuity; selecting GNSS signals according to the number of available GNSS signals; and performing smoothing processing on the selected GNSS signal based on the historical information. According to the method provided by the invention, the GNSS signals with the RTK function are fused, and compared with common GNSS signal fusion, the GNSS signals with the RTK function have higher precision and have higher difficulty in identifying whether positioning is accurate or not.

Description

Technical Field

[0001] The present invention relates to the field of information processing technology, and specifically discloses a multi-GNSS fusion positioning method and system. Background Art

[0002] As the cornerstone module of autonomous driving, the positioning system has extremely high requirements for its reliability. GNSS signal is the most important component of exogenous positioning. A system composed of a single GNSS can easily fail due to GNSS signal blocking, reflection, or differential signal transmission errors, causing potential risks to the system. A multi-GNSS system can effectively reduce the possibility of such risks.

[0003] When distinguishing and selecting multiple GNSS signals, the positioning module is prone to sudden changes in vehicle posture due to the switching of the received GNSS signal source. This situation poses a huge risk to the downstream path planning system and may cause the control signal of the autonomous driving vehicle to jump and cause danger, making the risk of autonomous driving failure high. Therefore, an effective GNSS switching strategy can make the positioning output more continuous and reduce the risk of failure of the autonomous driving system.

[0004] At present, there is no patent related to the fusion of multi-GNSS technologies related to autonomous driving. The relevant patent application with patent number CN202410336924.2 proposes a GNSS multi-mode positioning method. Compared with the method proposed in this invention, this method has the following differences:

[0005] 1) This method does not fully consider the impact of the continuity between positioning on autonomous driving;

[0006] 2) This method only fuses ordinary GNSS.

[0007] Therefore, how to solve the problem of weak anti-interference ability of a single GNSS system in the prior art during actual use and the impact on the downstream when multiple GNSS systems are integrated is a technical problem that needs to be urgently solved by those skilled in the art. Summary of the invention

[0008] To achieve the purpose of the present invention, the present application provides a multi-GNSS fusion positioning method, including:

[0009] Step S1: determining available GNSS signals according to the real-time performance, status bit signal and spatial continuity of the GNSS signals;

[0010] Step S2: selecting a GNSS signal according to the number of available GNSS signals;

[0011] Step S3: Smoothing the selected GNSS signal based on historical information.

[0012] In some specific embodiments, step S1 includes:

[0013] Step S11: demodulate the acquisition time of the GNSS signal from the GNSS signal and compare it with the current system time. If the time difference is less than or equal to the threshold, the current GNSS signal is a real-time signal; if the time difference is greater than the threshold, the current GNSS signal is unavailable;

[0014] Step S12: judging the status bit signal of the GNSS signal through the status bit signal of the RTK differential result; if the status bit signal of the current GNSS signal is not in the floating point solution state, the current GNSS signal is unavailable;

[0015] Step S13: According to the GNSS posture information and status information at the previous moment and the current moment, and according to the IMU information at the current moment, determine whether the status information at the previous moment and the current moment is an integer solution. If the status information at the previous moment and the current moment are both integer solutions, calculate the track based on the posture information at the previous moment and the IMU information, and determine the prior posture at the current moment. If the angle or position error between the prior posture and the posture information returned by the GNSS at the current moment is greater than a certain threshold, the current GNSS signal is unavailable.

[0016] In some specific embodiments, step S2 includes:

[0017] When there is only one GNSS signal available, the current GNSS signal is selected for positioning;

[0018] When multiple GNSS signals are available, the spatial continuity of the multiple GNSS signals is judged, and the GNSS signal with the pose closest to the prior pose is selected as the GNSS used downstream;

[0019] When no GNSS is available, a secondary failure judgment is performed on the GNSS signal.

[0020] In some specific embodiments, the secondary failure judgment includes:

[0021] Detecting a non-real-time GNSS signal, if the non-real-time GNSS signal meets the requirements of status bit information and spatial continuity, using the non-real-time GNSS signal, determining that the system time may be wrong, and generating a danger signal to transmit to the watchdog system;

[0022] The status bit information is judged. If the GNSS information has a floating point solution determined by spatial continuity, the GNSS information is output, and a signal indicating that the positioning is about to fail is transmitted to the watchdog system.

[0023] Otherwise, the status bit information is directly judged, high-precision GNSS information is returned first, and a signal requesting takeover that the positioning has failed is transmitted to the watchdog system.

[0024] In some specific embodiments, step S3 includes: determining an error value to be smoothed according to a transformation matrix of the GNSS signal being used and to be switched relative to the origin, wherein the error value is determined according to the following formula:

[0025] delta=A0 -1 B0

[0026] Where delta is the error value, A0 is the transformation matrix of the GNSS signal being used relative to the origin, and B0 is the transformation matrix of the GNSS signal to be switched relative to the origin.

[0027] To achieve the same invention purpose, the present application also provides a multi-GNSS fusion positioning system, including:

[0028] Available signal judgment module: used to determine the available GNSS signals according to the real-time performance, status bit signal and spatial continuity of the GNSS signals;

[0029] Result output module: used to select GNSS signals according to the number of available GNSS signals;

[0030] Smoothing processing module: used to smooth the selected GNSS signal based on historical information.

[0031] In some specific embodiments, the available signal determination module is used to perform the following steps:

[0032] Step S11: demodulate the acquisition time of the GNSS signal from the GNSS signal and compare it with the current system time. If the time difference is less than or equal to the threshold, the current GNSS signal is a real-time signal; if the time difference is greater than the threshold, the current GNSS signal is unavailable;

[0033] Step S12: judging the status bit signal of the GNSS signal through the status bit signal of the RTK differential result; if the status bit signal of the current GNSS signal is not in the floating point solution state, the current GNSS signal is unavailable;

[0034] Step S13: According to the GNSS posture information and status information at the previous moment and the current moment, and according to the IMU information at the current moment, determine whether the status information at the previous moment and the current moment is an integer solution. If the status information at the previous moment and the current moment are both integer solutions, calculate the track based on the posture information at the previous moment and the IMU information, and determine the prior posture at the current moment. If the angle or position error between the prior posture and the posture information returned by the GNSS at the current moment is greater than a certain threshold, the current GNSS signal is unavailable.

[0035] In some specific embodiments, the result output module is used to perform the following operations:

[0036] When there is only one GNSS signal available, the current GNSS signal is selected for positioning;

[0037] When multiple GNSS signals are available, the spatial continuity of the multiple GNSS signals is judged, and the GNSS signal with the pose closest to the prior pose is selected as the GNSS used downstream;

[0038] When no GNSS is available, a secondary failure judgment is performed on the GNSS signal.

[0039] In some specific embodiments, the secondary failure judgment includes:

[0040] Detecting a non-real-time GNSS signal, if the non-real-time GNSS signal meets the requirements of status bit information and spatial continuity, using the non-real-time GNSS signal, determining that the system time may be wrong, and generating a danger signal to transmit to the watchdog system;

[0041] The status bit information is judged. If the GNSS information has a floating point solution determined by spatial continuity, the GNSS information is output, and a signal indicating that the positioning is about to fail is transmitted to the watchdog system.

[0042] Otherwise, the status bit information is directly judged, high-precision GNSS information is returned first, and a signal requesting takeover that the positioning has failed is transmitted to the watchdog system.

[0043] In some specific embodiments, the smoothing processing module is used to perform the following operations: determine the error value to be smoothed according to the transformation matrix of the GNSS signal being used and to be switched relative to the origin, and the error value is determined according to the following formula:

[0044] delta=A0 -1 B0

[0045] Where delta is the error value, A0 is the transformation matrix of the GNSS signal being used relative to the origin, and B0 is the transformation matrix of the GNSS signal to be switched relative to the origin.

[0046] Beneficial effects of the above technical solution:

[0047] This application improves the robustness of the positioning system by using multiple GNSS signal results for fusion selection, effectively solves the problem of weak anti-interference ability of a single GNSS signal, and reduces the risk of failure of the autonomous driving system. When switching GNSS signals, the downstream module's requirement for spatial continuity of GNSS signals is taken into account, which effectively improves the impact of multi-source GNSS signal switching on the downstream, ensuring that the downstream is unaware of the switching process. It prevents the control module from making unexpected behaviors during switching, thereby improving the safety and comfort of the autonomous driving system. The introduction of multiple GNSS signals has greatly improved the overall robustness of the positioning module, which is conducive to the safe and efficient operation of driverless vehicles on the road, greatly improving the production efficiency of the entire society.

[0048] The method proposed in this application is to fuse GNSS signals with RTK function. Compared with ordinary GNSS signal fusion, GNSS signals with RTK have higher accuracy and are more difficult to identify whether the positioning is accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0050] Figure 1 A flowchart of a multi-GNSS fusion positioning method provided by an embodiment of the present invention;

[0051] Figure 2 A schematic diagram of a GNSS signal determination process based on a multi-GNSS fusion positioning method provided by an embodiment of the present invention;

[0052] Figure 3 A schematic diagram of a GNSS signal selection process based on a multi-GNSS fusion positioning method provided by an embodiment of the present invention;

[0053] Figure 4 A schematic diagram of a GNSS signal switching effect based on a multi-GNSS fusion positioning method provided by an embodiment of the present invention;

[0054] Figure 5 A structural diagram of a multi-GNSS fusion positioning system is provided for one embodiment of the present invention. DETAILED DESCRIPTION

[0055] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0056] Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar symbols throughout represent the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0057] Embodiment 1

[0058] An embodiment of the present invention provides a multi-GNSS fusion positioning method, including:

[0059] Step S1: Determine available GNSS signals according to the real-time performance, status bit signal and spatial continuity of the GNSS signals.

[0060] In a specific embodiment of the present invention, referring to Figure 2 As shown, step S1 includes:

[0061] Step S11: demodulate the acquisition time of the GNSS signal from the GNSS signal and compare it with the current system time. If the time difference is less than or equal to the threshold, the current GNSS signal is a real-time signal; if the time difference is greater than the threshold, the current GNSS signal is unavailable.

[0062] Step S12: judging the status bit signal of the GNSS signal through the status bit signal of the RTK differential result; if the status bit signal of the current GNSS signal is not in the floating point solution state, the current GNSS signal is unavailable.

[0063] Specifically, the RTK differential information will return the settlement of the carrier phase ambiguity, which can generally be divided into four states: integer solution: means that the carrier phase ambiguity has been settled as an integer, and the current GNSS signal output result is at the centimeter level; floating point solution: means that the current carrier ambiguity can only be solved as a floating point number, and the accuracy is usually at the decimeter level; single point positioning: no RTK signal is received, it is a traditional single-point GNSS signal solution, and the accuracy is at the meter level; differential correction: using pseudo-range correction results, the accuracy is sub-meter level. Since autonomous driving has high requirements for positioning accuracy, the RTK differential status bit is judged from the GNSS signal message. If it is not in the floating point solution state, the current GNSS signal is considered unavailable.

[0064] Step S13: According to the GNSS posture information and status information at the previous moment and the current moment, and according to the IMU information at the current moment, determine whether the status information at the previous moment and the current moment is an integer solution. If the status information at the previous moment and the current moment are both integer solutions, calculate the track based on the posture information at the previous moment and the IMU information, and determine the prior posture at the current moment. If the angle or position error between the prior posture and the posture information returned by the GNSS at the current moment is greater than a certain threshold, the current GNSS signal is unavailable.

[0065] Specifically, although RTK often has centimeter-level accuracy, there are still cases of false alarms in the status position. Therefore, it is still necessary to judge the spatial continuity of the GNSS results. The specific judgment method is as follows: record the GNSS pose information at the previous moment as P t-1 , the status bit is X t-1 , the GNSS pose information at the current moment is P t , the status bit is X t At the current moment, the velocity and angular velocity returned by the IMU are v t ,w t , then when the state bits at both moments are integer solutions, the trajectory is calculated based on the posture information of the previous moment and the IMU information to obtain the prior posture of the current moment If the prior pose and the P returned by GNSS at the current moment t If the angle or position error is greater than a certain threshold, the GNSS result is considered discontinuous and the GNSS is considered unavailable.

[0066] Step S2: Selecting a GNSS signal according to the number of available GNSS signals.

[0067] In a specific embodiment of the present invention, referring to Figure 3 As shown, step S2 includes:

[0068] When there is only one GNSS signal available, the current GNSS signal is selected for positioning;

[0069] When multiple GNSS signals are available, the spatial continuity of the multiple GNSS signals is judged, and the GNSS signal with the pose closest to the prior pose is selected as the GNSS used downstream;

[0070] When no GNSS is available, a secondary failure judgment is performed on the GNSS signal.

[0071] In a specific embodiment of the present invention, the secondary failure judgment includes:

[0072] Detecting a non-real-time GNSS signal, if the non-real-time GNSS signal meets the requirements of status bit information and spatial continuity, using the non-real-time GNSS signal, determining that the system time may be wrong, and generating a danger signal to transmit to the watchdog system;

[0073] The status bit information is judged. If the GNSS information has a floating point solution determined by spatial continuity, the GNSS information is output, and a signal indicating that the positioning is about to fail is transmitted to the watchdog system.

[0074] Otherwise, the status bit information is directly judged, high-precision GNSS information is returned first, and a signal requesting takeover that the positioning has failed is transmitted to the watchdog system.

[0075] Step S3: Smoothing the selected GNSS signal based on historical information.

[0076] In a specific embodiment of the present invention, step S3 includes: determining the error value to be smoothed according to the transformation matrix of the GNSS signal being used and to be switched relative to the origin, wherein the error value is determined according to the following formula:

[0077] delta=A0 -1 B0

[0078] Where delta is the error value, A0 is the transformation matrix of the GNSS signal being used relative to the origin, and B0 is the transformation matrix of the GNSS signal to be switched relative to the origin.

[0079] Specifically, after the GNSS signal is selected, simply outputting the GNSS result may cause a jump in the positioning result. Therefore, the output result of the GNSS signal is smoothed based on historical information to ensure that the downstream module can accept the switching of the positioning information without feeling. The specific implementation method is as follows:

[0080] Assuming that the time to prepare for switching is frame 0, the transformation matrices of the GNSS being used and to be switched relative to the origin are A0B0 respectively, then the error value that needs to be smoothed can be calculated as:

[0081] delta=A0 -1 B0

[0082] After taking out the 6-DOF pose information from the transformation matrix, the errors that need to be smoothed for each DOF are x, y, z, φ, θ, and ψ. Assuming that the maximum smoothable errors of each frame are Δx, Δy, Δz, Δφ, Δθ, and Δψ, the smoothed error amount for the x dimension in the tth frame is min(Δx*t,x). The same is true for other dimensions. Based on the smoothing amount of this frame, the matrix T used for frame smoothing is constructed.t , then the transformation matrix relative to the origin output by the smoothing module is:

[0083] O t =A0*T t *B0 -1 *B t

[0084] When the error smoothing amount of all dimensions is equal to the error amount, the process ends and the result B of the current GNSS after switching is directly output. t .

[0085] like Figure 4 As shown, when the GNSS used is changed from a GNSS with a relatively upper trajectory to a GNSS with a relatively lower trajectory, the trajectory will switch smoothly without any jumps.

[0086] This application improves the robustness of the positioning system by using multiple GNSS signal results for fusion selection, effectively solves the problem of weak anti-interference ability of a single GNSS signal, and reduces the risk of failure of the autonomous driving system. When switching GNSS signals, the downstream module's requirement for spatial continuity of GNSS signals is taken into account, which effectively improves the impact of multi-source GNSS signal switching on the downstream, ensuring that the downstream is unaware of the switching process. It prevents the control module from making unexpected behaviors during switching, thereby improving the safety and comfort of the autonomous driving system. The introduction of multiple GNSS signals has greatly improved the overall robustness of the positioning module, which is conducive to the safe and efficient operation of driverless vehicles on the road, greatly improving the production efficiency of the entire society.

[0087] Embodiment 2

[0088] An embodiment of the present invention provides a multi-GNSS fusion positioning system, referring to Figure 5 As shown, including:

[0089] Available signal determination module 10: used to determine available GNSS signals according to the real-time performance, status bit signal and spatial continuity of the GNSS signals;

[0090] The result output module 20 is used to select a GNSS signal according to the number of available GNSS signals;

[0091] The smoothing processing module 30 is used to perform smoothing processing on the selected GNSS signal based on the historical information.

[0092] In some specific embodiments, the available signal determination module 10 is used to perform the following steps:

[0093] Step S11: demodulate the acquisition time of the GNSS signal from the GNSS signal and compare it with the current system time. If the time difference is less than or equal to the threshold, the current GNSS signal is a real-time signal; if the time difference is greater than the threshold, the current GNSS signal is unavailable;

[0094] Step S12: judging the status bit signal of the GNSS signal through the status bit signal of the RTK differential result; if the status bit signal of the current GNSS signal is not in the floating point solution state, the current GNSS signal is unavailable;

[0095] Step S13: According to the GNSS posture information and status information at the previous moment and the current moment, and according to the IMU information at the current moment, determine whether the status information at the previous moment and the current moment is an integer solution. If the status information at the previous moment and the current moment are both integer solutions, calculate the track based on the posture information at the previous moment and the IMU information, and determine the prior posture at the current moment. If the angle or position error between the prior posture and the posture information returned by the GNSS at the current moment is greater than a certain threshold, the current GNSS signal is unavailable.

[0096] In some specific embodiments, the result output module 20 is used to perform the following operations:

[0097] When there is only one GNSS signal available, the current GNSS signal is selected for positioning;

[0098] When multiple GNSS signals are available, the spatial continuity of the multiple GNSS signals is judged, and the GNSS signal with the pose closest to the prior pose is selected as the GNSS used downstream;

[0099] When no GNSS is available, a secondary failure judgment is performed on the GNSS signal.

[0100] In some specific embodiments, the secondary failure judgment includes:

[0101] Detecting a non-real-time GNSS signal, if the non-real-time GNSS signal meets the requirements of status bit information and spatial continuity, using the non-real-time GNSS signal, determining that the system time may be wrong, and generating a danger signal to transmit to the watchdog system;

[0102] The status bit information is judged. If the GNSS information has a floating point solution determined by spatial continuity, the GNSS information is output, and a signal indicating that the positioning is about to fail is transmitted to the watchdog system.

[0103] Otherwise, the status bit information is directly judged, high-precision GNSS information is returned first, and a signal requesting takeover that the positioning has failed is transmitted to the watchdog system.

[0104] In some specific embodiments, the smoothing processing module 30 is used to perform the following operations: determine the error value to be smoothed according to the transformation matrix of the GNSS signal being used and to be switched relative to the origin, and the error value is determined according to the following formula:

[0105] delta=A0 -1 B0

[0106] Where delta is the error value, A0 is the transformation matrix of the GNSS signal being used relative to the origin, and B0 is the transformation matrix of the GNSS signal to be switched relative to the origin.

[0107] This application improves the robustness of the positioning system by using multiple GNSS signal results for fusion selection, effectively solves the problem of weak anti-interference ability of a single GNSS signal, and reduces the risk of failure of the autonomous driving system. When switching GNSS signals, the downstream module's requirement for spatial continuity of GNSS signals is taken into account, which effectively improves the impact of multi-source GNSS signal switching on the downstream, ensuring that the downstream is unaware of the switching process. It prevents the control module from making unexpected behaviors during switching, thereby improving the safety and comfort of the autonomous driving system. The introduction of multiple GNSS signals has greatly improved the overall robustness of the positioning module, which is conducive to the safe and efficient operation of driverless vehicles on the road, greatly improving the production efficiency of the entire society.

[0108] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

[0109] Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referenced to each other. The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of the methods, terminal devices (systems), and computer program products according to the embodiments of the present invention. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing terminal device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal device generate instructions for implementing the functions in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be stored in a computer-readable memory that can guide a computer or other programmable data processing terminal device to work in a specific way, so that the instructions stored in the computer-readable memory produce a product including an instruction device, which implements the functions specified in the process. Figure 1 A process or multiple processes and / or boxes Figure 1 These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device, so that a series of operation steps are executed on the computer or other programmable terminal device to produce a computer-implemented process, so that the instructions executed on the computer or other programmable terminal device provide for implementing the process in the process. Figure 1 A process or multiple processes and / or boxes Figure 1The steps of the functions specified in one or more boxes. Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention. Finally, it should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or terminal device including a series of elements includes not only those elements, but also other elements that are not explicitly listed, or also includes elements inherent to such process, method, article or terminal device. In the absence of more restrictions, the elements defined by the sentence "including one..." do not exclude the existence of other identical elements in the process, method, article or terminal device including the elements.

[0110] The method and device provided by the present invention are introduced in detail above. Specific examples are used in this article to illustrate the principle and implementation mode of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

[0111] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", "one specific embodiment" or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit it. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A multi-GNSS fusion positioning method, characterized in that: include: Step S1: determining available GNSS signals according to the real-time performance, status bit signal and spatial continuity of the GNSS signals; Step S2: selecting a GNSS signal according to the number of available GNSS signals; Step S3: Smoothing the selected GNSS signal based on historical information.

2. The multi-GNSS fusion positioning method according to claim 1, characterized in that: Step S1 includes: Step S11: demodulate the acquisition time of the GNSS signal from the GNSS signal and compare it with the current system time. If the time difference is less than or equal to the threshold, the current GNSS signal is a real-time signal; if the time difference is greater than the threshold, the current GNSS signal is unavailable; Step S12: judging the status bit signal of the GNSS signal through the status bit signal of the RTK differential result; if the status bit signal of the current GNSS signal is not in the floating point solution state, the current GNSS signal is unavailable; Step S13: According to the GNSS posture information and status information at the previous moment and the current moment, and according to the IMU information at the current moment, determine whether the status information at the previous moment and the current moment is an integer solution. If the status information at the previous moment and the current moment are both integer solutions, calculate the track based on the posture information at the previous moment and the IMU information, and determine the prior posture at the current moment. If the angle or position error between the prior posture and the posture information returned by the GNSS at the current moment is greater than a certain threshold, the current GNSS signal is unavailable.

3. The multi-GNSS fusion positioning method according to claim 1, characterized in that: Step S2 includes: When there is only one GNSS signal available, the current GNSS signal is selected for positioning; When multiple GNSS signals are available, the spatial continuity of the multiple GNSS signals is judged, and the GNSS signal with the pose closest to the prior pose is selected as the GNSS used downstream; When no GNSS is available, a secondary failure judgment is performed on the GNSS signal.

4. The multi-GNSS fusion positioning method according to claim 3 is characterized in that: The secondary failure judgment includes: Detecting a non-real-time GNSS signal, if the non-real-time GNSS signal meets the requirements of status bit information and spatial continuity, using the non-real-time GNSS signal, determining that the system time may be wrong, and generating a danger signal to transmit to the watchdog system; The status bit information is judged. If the GNSS information has a floating point solution determined by spatial continuity, the GNSS information is output, and a signal indicating that the positioning is about to fail is transmitted to the watchdog system. Otherwise, the status bit information is directly judged, high-precision GNSS information is returned first, and a signal requesting takeover that the positioning has failed is transmitted to the watchdog system.

5. The multi-GNSS fusion positioning method according to claim 1, characterized in that: Step S3 includes: determining the error value to be smoothed according to the transformation matrix of the GNSS signal being used and to be switched relative to the origin, wherein the error value is determined according to the following formula: delta=A0 -1 B0 Where delta is the error value, A0 is the transformation matrix of the GNSS signal being used relative to the origin, and B0 is the transformation matrix of the GNSS signal to be switched relative to the origin.

6. A multi-GNSS fusion positioning system, characterized in that: include: Available signal judgment module: used to determine the available GNSS signals according to the real-time performance, status bit signal and spatial continuity of the GNSS signals; Result output module: used to select GNSS signals according to the number of available GNSS signals; Smoothing processing module: used to smooth the selected GNSS signal based on historical information.

7. The multi-GNSS fusion positioning system according to claim 6, characterized in that: The available signal determination module is used to perform the following steps: Step S11: demodulate the acquisition time of the GNSS signal from the GNSS signal and compare it with the current system time. If the time difference is less than or equal to the threshold, the current GNSS signal is a real-time signal; if the time difference is greater than the threshold, the current GNSS signal is unavailable; Step S12: judging the status bit signal of the GNSS signal through the status bit signal of the RTK differential result; if the status bit signal of the current GNSS signal is not in the floating point solution state, the current GNSS signal is unavailable; Step S13: According to the GNSS posture information and status information at the previous moment and the current moment, and according to the IMU information at the current moment, determine whether the status information at the previous moment and the current moment is an integer solution. If the status information at the previous moment and the current moment are both integer solutions, calculate the track based on the posture information at the previous moment and the IMU information, and determine the prior posture at the current moment. If the angle or position error between the prior posture and the posture information returned by the GNSS at the current moment is greater than a certain threshold, the current GNSS signal is unavailable.

8. The multi-GNSS fusion positioning system according to claim 6, characterized in that: The result output module is used to perform the following operations: When there is only one GNSS signal available, the current GNSS signal is selected for positioning; When multiple GNSS signals are available, the spatial continuity of the multiple GNSS signals is judged, and the GNSS signal with the pose closest to the prior pose is selected as the GNSS used downstream; When no GNSS is available, a secondary failure judgment is performed on the GNSS signal.

9. The multi-GNSS fusion positioning system according to claim 8, characterized in that: The secondary failure judgment includes: Detecting a non-real-time GNSS signal, if the non-real-time GNSS signal meets the requirements of status bit information and spatial continuity, using the non-real-time GNSS signal, determining that the system time may be wrong, and generating a danger signal to transmit to the watchdog system; The status bit information is judged. If the GNSS information has a floating point solution determined by spatial continuity, the GNSS information is output, and a signal indicating that the positioning is about to fail is transmitted to the watchdog system. Otherwise, the status bit information is directly judged, high-precision GNSS information is returned first, and a signal requesting takeover that the positioning has failed is transmitted to the watchdog system.

10. The multi-GNSS fusion positioning system according to claim 6, characterized in that: The smoothing processing module is used to perform the following operations: determine the error value to be smoothed according to the transformation matrix of the GNSS signal being used and to be switched relative to the origin, and the error value is determined according to the following formula: delta=A0 -1 B0 Where delta is the error value, A0 is the transformation matrix of the GNSS signal being used relative to the origin, and B0 is the transformation matrix of the GNSS signal to be switched relative to the origin.

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