Method for resolving and maintaining a GNSS coordinate reference frame and device therefor

Abstract

The application discloses a kind of GNSS coordinate reference frame resolving and maintaining method, comprising: selecting partial ITRF station, combine reference station to be resolved, constitute the coordinate reference frame;The range covered by the coordinate reference frame is divided into several regions, then each region is divided into several subnets, wherein, each subnet in the same region includes the same ITRF station as constraint station, for frame constraint;Under the frame constraint, double difference network solution is carried out to each subnet respectively, and the subnet single-day solution coordinates of each subnet are obtained;The subnet single-day solution coordinates of each subnet are merged respectively, and the whole network single-day solution coordinates are obtained;The whole network single-day solution coordinates of one week seven days are merged, and the reference station weekly solution coordinates of the coordinate reference frame are obtained. Through zoning and netting strategy, the network structure is optimized, the two kinds of position enhancement services of SSR and OSR can be satisfied simultaneously, and the resolving accuracy, stability and efficiency are improved.

Description

Technical Field

[0001] This application relates to the field of location service technology, and in particular to a GNSS coordinate reference frame calculation and maintenance technology. Background Technology

[0002] High-precision positioning services require an accurate reference system. The Terrestrial Reference System (TRS) is fundamental to a range of Earth studies; the position and motion of an object on Earth at any given time can be described using the TRS. An ideal Terrestrial Reference System is a mathematical model defined by its origin, scale factor, orientation at a given time, and their evolution over time. The Earth Reference Frame is the physical implementation of the Terrestrial Reference System, consisting of a set of stations with known coordinates and velocities distributed across the Earth's surface. The Earth Reference Frame provides a unified reference benchmark for various positioning services.

[0003] The International Terrestrial Reference Frame (ITRF) is widely recognized as the most accurate and stable Earth reference frame. It was developed to meet the needs of geodynamic studies of the Earth's shape and dynamic characteristics, providing a long-term, absolute reference benchmark. The ITRF also forms the basis for other regional reference frames. However, despite its high accuracy and stability, the density and distribution of its reference stations are far from sufficient to meet the requirements for high-precision positioning services.

[0004] Self-built reference frames typically utilize certain ITRF stations within the ITRF framework that possess high data accuracy and stable, long-term observation data as a foundation. These stations are then combined with self-deployed reference stations for joint measurements to obtain an enhanced coordinate reference frame. Self-built reference frames can meet the needs of high-precision positioning and navigation for specific regions and services.

[0005] my country's latest reference frame is CGCS2000 (National Geodetic Coordinate System 2000), a regional coordinate frame based on ITRF1997, which initially meets the needs of national economic construction, social development, national defense, and scientific research. However, CGCS2000 is still a regional reference frame and cannot provide a benchmark for global positioning services. In addition, CGCS2000 is a static frame, and most reference stations only have coordinate information, lacking velocity field information.

[0006] Other regional reference frames may have more problems. For example, regional reference frames have limited coverage and can only provide a benchmark for location services within the corresponding area; some regional reference frames have low standards for the construction of their base stations, resulting in poor stability of the frame, and so on.

[0007] Therefore, there is an urgent need for a solution and maintenance scheme for a large-scale GNSS coordinate reference frame for multiple location enhancement services. Summary of the Invention

[0008] The purpose of this application is to provide a method for solving and maintaining a GNSS coordinate reference frame. By using a segmentation and network strategy to optimize the network structure, it can simultaneously satisfy both SSR and OSR location augmentation services, thereby improving the accuracy, stability and efficiency of the solution.

[0009] To address the aforementioned technical problems, this application discloses a method for solving and maintaining a GNSS coordinate reference frame, comprising the following steps:

[0010] Select a portion of ITRF stations and combine them with the reference stations to be calculated to form the coordinate reference frame; wherein, the ITRF stations are used to fix the coordinate reference frame;

[0011] The area covered by the coordinate reference frame is divided into several regions, and each region is further divided into several subnets. Each subnet within the same region includes the same ITRF station as a constraint station for frame constraint.

[0012] Under the framework constraints, the double-difference network solution is performed on each subnet to obtain the subnet single-day solution coordinates for each subnet;

[0013] The single-day solution coordinates of each subnet are merged to obtain the single-day solution coordinates of the entire network;

[0014] By merging the daily coordinates of the entire network for seven days, the weekly coordinates of the reference station of the coordinate reference frame are obtained.

[0015] In another preferred embodiment, the step of dividing the area covered by the coordinate reference frame into several regions, and then dividing each region into several subnets, includes the following sub-steps:

[0016] The area covered by the coordinate reference frame is divided into several regions, and it is determined whether the distribution of reference stations in each region is uniform. Regions with uneven distribution of reference stations are further divided until the reference stations in each region are evenly distributed.

[0017] Determine whether the number of reference stations in each region is greater than the first threshold. If so, divide the region into several subnets using the maximum density subnetting method.

[0018] In another preferred embodiment, the step of dividing the area covered by the coordinate reference frame into several regions includes the following sub-steps:

[0019] Based on the site distance clustering partitioning method or the segmentation method, the area covered by the coordinate reference frame is divided into several regions.

[0020] In another preferred embodiment, the step of merging the single-day solution coordinates of each subnet to obtain the single-day solution coordinates of the entire network includes the following sub-steps:

[0021] The subnet single-day solution coordinates are merged into the whole network single-day solution coordinates using the normal equation superposition algorithm.

[0022] In another preferred embodiment, the step of merging the daily coordinates of the entire network for seven days to obtain the weekly coordinates of the reference station of the coordinate reference frame includes the following sub-steps:

[0023] Based on time series analysis, the robust daily solution coordinates of the entire network are merged into weekly solution coordinates using a normal equation superposition algorithm.

[0024] In another preferred embodiment, the step of robustly combining the time-series-based single-day solution coordinates of the robust network into weekly solution coordinates using a normal equation superposition algorithm includes the following sub-steps:

[0025] Obtain the daily solution for each base station from the daily solution of the whole network, sort the daily solution coordinates of each base station for seven days of the week in chronological order, and determine whether the difference between the maximum and minimum values ​​of the daily solution coordinates for seven days of the week is greater than the relocation identification threshold.

[0026] If so, the daily solution coordinates of the base station for seven days of the week are grouped, the epoch information of the daily solution coordinates that are close to the maximum value are assigned to the first group, the epoch information of the daily solution coordinates that are close to the minimum value are assigned to the second group, and it is determined whether all the epoch information in the first group is greater than or less than all the epoch information in the second group.

[0027] If so, it is determined that the base station has changed position, and it is further determined whether the number of epoch information in the first group is greater than the number of epoch information in the second group;

[0028] If the number of epochs in the first group is greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the first group; if the number of epochs in the first group is not greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the second group.

[0029] Gross errors are detected in the retained single-day solution coordinates, and the detected gross errors are removed.

[0030] The mean of the remaining single-day solution coordinates after removing outliers is used as the initial a priori value. It is then determined whether the difference between each remaining single-day solution coordinate and the initial a priori value is greater than a second threshold. If it is greater than the second threshold, the single-day solution coordinate is discarded; if it is not greater than the second threshold, the single-day solution coordinate is retained.

[0031] The daily coordinates retained within the seven days of the week are merged to obtain the weekly coordinates of the base station.

[0032] In another preferred embodiment, the following steps are also included:

[0033] The coordinates of the coordinate reference frame are updated using the aforementioned Zhou Jie coordinates.

[0034] In another preferred embodiment, the step of updating the coordinates of the coordinate reference frame using the circumferential coordinates includes the following sub-steps:

[0035] Every first time interval, the coordinates of the coordinate reference frame are updated using the weekly coordinates of all the reference stations of the coordinate reference frame.

[0036] Within the first time interval, every second time interval, the weekly coordinates of the base stations whose weekly coordinate changes exceed the third threshold are updated in real time; wherein, the first time interval is longer than the second time interval.

[0037] In another preferred embodiment, the step of selecting a subset of ITRF stations includes the following sub-steps:

[0038] Select ITRF stations whose distribution range covers the coordinate reference frame, and whose coordinate position residuals are less than 5 mm and velocity residuals are less than 3 mm / year.

[0039] The embodiments of this application also disclose a GNSS coordinate reference frame calculation and maintenance device, comprising:

[0040] The selection module is used to select a portion of ITRF stations and combine them with the reference stations to be calculated to form the coordinate reference frame; wherein, the ITRF stations are used to fix the coordinate reference frame;

[0041] The sub-region module is used to divide the area covered by the coordinate reference frame into several regions, and then divide each region into several sub-networks. In each sub-network within the same region, the same ITRF station is included as a constraint station for frame constraint.

[0042] The subnet single-day solution coordinate calculation module is used to perform double-difference network solution for each subnet under the framework constraints to obtain the subnet single-day solution coordinates for each subnet.

[0043] The whole network single-day solution coordinate calculation module is used to merge the subnet single-day solution coordinates of each subnet to obtain the whole network single-day solution coordinates;

[0044] The weekly coordinate calculation module is used to merge the daily coordinates of the entire network for seven days in a week to obtain the weekly coordinates of the base station of the coordinate reference frame.

[0045] The main differences and effects of the implementation method of this application compared with the prior art are as follows:

[0046] The present application discloses a method for solving and maintaining a GNSS coordinate reference frame. By using a segmentation and network strategy to optimize the network structure, it can simultaneously satisfy both SSR and OSR location augmentation services, thereby improving the accuracy, stability and efficiency of the solution.

[0047] Furthermore, considering the characteristics of the large number, wide distribution, and uneven density of reference stations to be solved in the reference frame, this application proposes a zoned network strategy to optimize the network structure and improve the solution accuracy.

[0048] Furthermore, the embodiments of this application utilize multiple robust processing to solve the problem of unstable single-day coordinate calculation of the reference frame, thereby obtaining smooth and stable weekly coordinates of the reference station.

[0049] Furthermore, the embodiments of this application design a high-frequency update scheme for the coordinate frame reference station coordinates, which maintains the real-time performance of the coordinate reference frame and can eliminate the influence of periodic motion and non-structural motion.

[0050] The specification of this application contains numerous technical features distributed across various technical solutions. Listing all possible combinations of these technical features (i.e., technical solutions) would make the specification excessively lengthy. To avoid this problem, the various technical features disclosed in the above-described invention, the various technical features disclosed in the following embodiments and examples, and the various technical features disclosed in the accompanying drawings can be freely combined to form various new technical solutions (all of which are considered to have been described in this specification), unless such a combination of technical features is technically infeasible. For example, one example discloses feature A+B+C, and another example discloses feature A+B+D+E. Features C and D are equivalent technical means that serve the same function, and technically only one needs to be used; they cannot be used simultaneously. Feature E can technically be combined with feature C. Therefore, the solution A+B+C+D should not be considered as described because it is technically infeasible, while the solution A+B+C+E should be considered as described. Attached Figure Description

[0051] Figure 1This is a flowchart illustrating a method for solving and maintaining a GNSS coordinate reference frame according to the first embodiment of this application;

[0052] Figure 2 This is a schematic diagram of a partition in the first embodiment of this application;

[0053] Figure 3 This is a schematic diagram of a network subdivision in the first embodiment of this application;

[0054] Figure 4 This is a schematic diagram of the epoch information grouping of the single-day solution coordinates of a base station for seven days of a week, in a preferred embodiment of the first implementation of this application.

[0055] Figure 5 This is a schematic diagram of epoch information grouping for the single-day coordinate solution of a base station for seven days of a week, in another preferred embodiment of the first implementation of this application.

[0056] Figure 6 This is a flowchart illustrating the overall technical solution of another preferred embodiment of the first implementation of this application;

[0057] Figure 7 This is a schematic diagram of a high-frequency full update and partial update of coordinate reference frame base station coordinates in another preferred embodiment of the first embodiment of this application.

[0058] Figure 8 This is a schematic diagram of the structure of a GNSS coordinate reference frame calculation and maintenance device according to the second embodiment of this application. Detailed Implementation

[0059] In the following description, numerous technical details are presented to facilitate the reader's understanding of this application. However, those skilled in the art will understand that the technical solutions claimed in the claims of this application can be implemented even without these technical details and with various variations and modifications based on the following embodiments.

[0060] Explanation of some concepts:

[0061] GNSS: Global Navigation Satellite System.

[0062] Coordinate reference frame: The physical implementation of a coordinate system, represented by the coordinates and velocities of a set of stations located on the Earth's surface.

[0063] Velocity field: the velocity of a group of (measuring) points.

[0064] SSR: State Space Representation.

[0065] OSR: Observation Space Representation.

[0066] ITRF: International Terrestrial Reference Frame.

[0067] TRS: Terrestrial Reference System.

[0068] Single-day coordinate solution: refers to the position coordinates of a station obtained by solving the observation values ​​of a station in one day.

[0069] Weekly coordinates: These are the position coordinates of a station obtained by calculating the observation values ​​of a station over a continuous week (seven days).

[0070] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0071] The first embodiment of this application relates to a method for solving and maintaining a GNSS coordinate reference frame. Figure 1 This is a flowchart illustrating the solution and maintenance method of the GNSS coordinate reference frame.

[0072] Specifically, such as Figure 1 As shown, the method for solving and maintaining the GNSS coordinate reference frame includes the following steps:

[0073] In step 101, a portion of ITRF stations are selected and combined with the reference stations to be calculated to form the coordinate reference frame; wherein, the ITRF stations are used to fix the coordinate reference frame.

[0074] In this embodiment, preferably, the step of "selecting a portion of ITRF stations" may further include the following sub-steps:

[0075] Select ITRF stations whose distribution range covers the coordinate reference frame, and whose coordinate position residuals are less than 5 mm and velocity residuals are less than 3 mm / year.

[0076] Then proceed to step 102, where the area covered by the coordinate reference frame is divided into several regions, and each region is further divided into several subnets. Each subnet within the same region includes the same ITRF station as a constraint station for frame constraint.

[0077] Figure 2 This is a partition diagram of one embodiment of the present invention. Figure 3 This is a schematic diagram of a network in this embodiment.

[0078] like Figure 2 and Figure 3 As shown, in this embodiment, preferably, step 102 may further include the following sub-steps:

[0079] The area covered by the coordinate reference frame is divided into several regions, and it is determined whether the distribution of reference stations in each region is uniform. Regions with uneven distribution of reference stations are further divided until the reference stations in each region are evenly distributed.

[0080] Determine whether the number of reference stations in each region is greater than the first threshold. If so, divide the region into several subnets using the maximum density subnetting method.

[0081] Furthermore, preferably, the step of "dividing the area covered by the coordinate reference frame into several regions" may further include the following sub-steps:

[0082] Based on the site distance clustering partitioning method or the segmentation method, the area covered by the coordinate reference frame is divided into several regions.

[0083] In view of the characteristics of the large number, wide distribution and uneven density of reference stations to be solved in the reference frame, this application proposes a zoned network strategy to optimize the network structure and improve the solution accuracy.

[0084] Then proceed to step 103, where double-difference network solutions are performed on each subnet under the framework constraints to obtain the subnet single-day solution coordinates for each subnet.

[0085] Then proceed to step 104, where the single-day solution coordinates of each subnet are merged to obtain the single-day solution coordinates of the entire network.

[0086] In this embodiment, preferably, step 104 may further include the following sub-steps:

[0087] The subnet single-day solution coordinates are merged into the whole network single-day solution coordinates using the normal equation superposition algorithm.

[0088] Then proceed to step 105, where the daily coordinates of the entire network for seven days are merged to obtain the weekly coordinates of the reference station of the coordinate reference frame.

[0089] In this embodiment, preferably, step 105 may further include the following sub-steps:

[0090] Based on time series analysis, the robust daily solution coordinates of the entire network are merged into weekly solution coordinates using a normal equation superposition algorithm.

[0091] Furthermore, preferably, the above step of "performing robustness based on time series and merging the robust whole network single-day solution coordinates into weekly solution coordinates using a normal equation superposition algorithm" may also include the following sub-steps:

[0092] Obtain the daily solution for each base station from the daily solution of the whole network. Sort the daily solution coordinates of each base station for seven days in a week according to time order. Determine whether the difference between the maximum and minimum values ​​of the daily solution coordinates for seven days in a week is greater than the relocation identification threshold.

[0093] If so, the daily solution coordinates of the base station for seven days of the week are grouped, the epoch information of the daily solution coordinates that are close to the maximum value are assigned to the first group, the epoch information of the daily solution coordinates that are close to the minimum value are assigned to the second group, and it is determined whether all the epoch information in the first group is greater than or less than all the epoch information in the second group.

[0094] If so, it is determined that the base station has changed position, and it is further determined whether the number of epoch information in the first group is greater than the number of epoch information in the second group.

[0095] If the number of epochs in the first group is greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the first group; if the number of epochs in the first group is not greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the second group.

[0096] Gross errors are detected in the retained single-day coordinates, and the detected gross errors are removed.

[0097] The mean of the remaining single-day solution coordinates after removing outliers is used as the initial prior value. It is then determined whether the difference between each remaining single-day solution coordinate and the initial prior value is greater than a second threshold. If it is greater than the second threshold, the single-day solution coordinate is discarded; if it is not greater than the second threshold, the single-day solution coordinate is retained.

[0098] The daily coordinates retained within the seven days of the week are merged to obtain the weekly coordinates of the base station.

[0099] Through the aforementioned sub-steps of "robust analysis based on time series, and merging the robust daily coordinates of the entire network into weekly coordinates using a normal equation superposition algorithm," it can be seen that when the difference between the maximum and minimum daily coordinates of a certain reference station over a seven-day week exceeds the relocation identification threshold, the logic for judging the location change of that reference station is entered. The epoch information of the daily coordinates of that reference station over a seven-day week is grouped according to whether it is closer to the maximum or minimum value. The epoch information of the daily coordinates closer to the maximum value is assigned to the first group, and the epoch information of the daily coordinates closer to the minimum value is assigned to the second group. If all epoch information in the first group is greater than or less than all epoch information in the second group, it is confirmed that the reference station has undergone a location change. The daily coordinates corresponding to the epoch information in the group with more epoch information are retained for subsequent gross error detection and other steps.

[0100] Figure 4 and Figure 5 The diagrams show the epoch information grouping of the daily solution coordinates of a base station for seven days of a week.

[0101] exist Figure 4 In the preferred embodiment shown, in the daily coordinates of the base station over a seven-day week, the daily coordinates of day 1 are the minimum, the daily coordinates of day 6 are the maximum, the daily coordinates of day 2 and day 3 are close to the minimum, and the daily coordinates of day 4, day 5, and day 7 are close to the maximum. Therefore, the epoch information of the daily coordinates of day 4, day 5, day 6, and day 7 is assigned to the first group, and the epoch information of the daily coordinates of day 1, day 2, and day 3 is assigned to the second group.

[0102] In this embodiment, preferably, the epoch information is time information.

[0103] Therefore, in Figure 4 In the preferred embodiment shown, [4,5,6,7] is the first group, and [1,2,3] is the second group. Furthermore, all epoch information within the first group is greater than all epoch information within the second group. Therefore, it is confirmed that the base station has undergone a positional change. In addition, because the first group contains more epoch information, the single-day coordinates corresponding to the epoch information in the first group are retained for subsequent gross error detection and other steps.

[0104] exist Figure 5In the preferred embodiment shown, in the daily coordinates of the base station over a seven-day week, the daily coordinates on day 4 are the maximum, the daily coordinates on day 6 are the minimum, and the daily coordinates on days 1, 2, 3, 5, and 7 are close to the minimum. Therefore, the epoch information of the daily coordinates on day 4 is assigned to the first group, and the epoch information of the daily coordinates on days 1, 2, 3, 5, 6, and 7 is assigned to the second group.

[0105] In this embodiment, preferably, the epoch information is time information.

[0106] Therefore, in Figure 5 In the preferred embodiment shown, [4] is the first group, and [1,2,3,5,6,7] is the second group. However, it is not satisfied that all epoch information in the first group is greater than or less than all epoch information in the second group. Therefore, it is confirmed that the base station has not changed position, and subsequent gross error detection and other steps are directly performed.

[0107] The implementation method of this application utilizes multiple robust processing to solve the problem of unstable single-day coordinate solution of the reference frame, thereby obtaining smooth and stable weekly coordinate solution of the reference station.

[0108] In this embodiment, preferably, the method for solving and maintaining the GNSS coordinate reference frame may further include the following steps:

[0109] The coordinates of the coordinate reference frame are updated using the aforementioned Zhou Jie coordinates.

[0110] Furthermore, preferably, the step of updating the coordinates of the coordinate reference frame using the aforementioned cyclic coordinates may further include the following sub-steps:

[0111] Every first time interval, the coordinates of the coordinate reference frame are updated using the weekly coordinates of all the reference stations of the coordinate reference frame.

[0112] Within the first time interval, every second time interval, the weekly coordinates of the base stations whose weekly coordinate changes exceed the third threshold are updated in real time; wherein, the first time interval is longer than the second time interval.

[0113] The embodiments of this application design a high-frequency update scheme for the coordinate frame reference station coordinates, which maintains the real-time performance of the coordinate reference frame and can eliminate the influence of periodic motion and non-structural motion.

[0114] This process will then end.

[0115] In summary, the implementation method of this application optimizes the network structure through a segmentation and networking strategy, which can simultaneously satisfy both SSR and OSR location enhancement services, thereby improving the solution accuracy, stability and efficiency.

[0116] To better understand the technical solution of this specification, a preferred embodiment will be described below. The details listed in this preferred embodiment are mainly for ease of understanding and are not intended to limit the scope of protection of this application.

[0117] First, it should be noted that the problems to be solved by this preferred embodiment include:

[0118] 1. In order to provide both SSR and OSR services simultaneously, the two services have different geographical coverage and different requirements for the density and distribution of base stations. The reference frame of this preferred embodiment needs to satisfy both services at the same time.

[0119] 2. When the coverage area of ​​the self-built reference frame is large, the number of reference stations is large, and their distribution is uneven, it will inevitably lead to defects such as poor reference station network structure and excessively long baselines. This will result in systematic biases and poor stability in the double-difference network solution. It is necessary to improve the network structure of the reference station double-difference network solution, reduce the possibility of baseline calculation errors and the impact of baseline calculation errors, and improve the accuracy, stability, and efficiency of the solution.

[0120] 3. In order to provide the solution to external parties, it is necessary to ensure that the solution is smooth, stable and highly accurate.

[0121] 4. The reference frame's base station is affected by tectonic and non-tectonic motions, requiring the real-time and dynamic nature of the reference frame to be maintained.

[0122] Figure 6 This is a flowchart illustrating the overall technical solution of the preferred embodiment.

[0123] Specifically, such as Figure 6 As shown, the technical solution of this preferred embodiment includes the following steps:

[0124] The ITRF series is currently recognized as the world's most accurate global reference frame. Although the global distribution of ITRF stations is relatively sparse, and the number in China is even smaller, making it difficult to meet usage needs, the ITRF framework can provide a unified reference benchmark for self-built global and regional Earth reference frames. Self-built reference frames provide a more precise description of the reference benchmark for specific services and regions, and can meet specific needs such as geophysical scientific research, surveying and mapping and meteorological services, and high-precision positioning and navigation services.

[0125] GNSS augmentation services based on BeiDou include ground-based OSR augmentation services and satellite-based SSR augmentation services. The OSR service area is China, requiring a large and dense network of CORS (Continuously Operating Reference Stations). Therefore, a reference frame covering China needs to be established and maintained for the OSR service. The SSR service area is global, with less stringent requirements for the density of reference CORS stations, but still requires the construction of many CORS stations worldwide to receive BeiDou signals and provide augmentation services. Therefore, a global reference frame needs to be established and maintained for the SSR service.

[0126] If the reference frames required for the two enhanced services mentioned above are solved separately, although both are aligned to ITRF2014, differences in constraint stations and solution strategies will lead to differences in the reference frames, making it difficult for different services to achieve high self-consistency. Therefore, this embodiment provides a high-precision dynamic frame solution and maintenance scheme that meets the needs of OSR / SSR services, taking into account the accuracy, consistency, stability, and computational efficiency of the reference frames.

[0127] Step 1: Select a portion of the ITRF stations to fix the entire reference frame.

[0128] A key objective of building and maintaining a self-built reference frame is to obtain the coordinates of stations within the ITRF frame with the highest possible accuracy and consistency. This embodiment uses the positions and velocities of a subset of ITRF stations to fix the entire self-built reference frame.

[0129] Generally, the selection of ITRF stations should meet the following conditions: 1) Select ITRF stations with good distribution and cover the area defined by the self-built reference frame; 2) The station has at least three years of long-term continuous observation; 3) Under various (at least 3) observation techniques, the station's coordinate position residual is less than 5 mm and the velocity residual is less than 3 mm / year.

[0130] When using an ITRF station for frame constraints, its coordinates need to be derived to the solution epoch. The derivation formula is as follows:

[0131] X tat =X ref +(T tar -T ref )×V (1)

[0132] Among them, X ref Here are the site's reference epoch coordinates within the ITRF framework, where V represents the site's velocity and T represents the epoch coordinates. ref For reference epochs, T tar To solve for the epoch, X tar Calculate epoch coordinates for the site within the ITRF framework.

[0133] Step 2: Perform zone and network calculations for all reference stations in the reference frame.

[0134] Because this reference frame needs to serve both SSR and OSR simultaneously, it suffers from an extremely large number of stations with highly uneven distribution. In double-difference network solutions, the network structure and constraints are crucial factors affecting solution accuracy. If a baseline error occurs, an inappropriate station structure may propagate the error to a large number of stations. Furthermore, the computational efficiency of double-difference network solutions decreases exponentially with the number of stations. Therefore, a reasonable partitioning strategy is essential for coordinate calculation.

[0135] The current mainstream network partitioning method is the maximum density to subnet (MDS) method used in GAMIT / GLOBK. This method is simple and fast, but it cannot eliminate network structure anomalies caused by uneven site distribution. Therefore, this preferred embodiment proposes a partitioning and networking algorithm. The specific process of the algorithm is as follows:

[0136] 1) Using certain methods, such as distance-based clustering or plate division, the world is divided into several regions, and it is determined whether the distribution of stations in each region is uniform. Regions with uneven station distribution need to be further divided until the requirement of uniformity of stations within the region is met.

[0137] 2) Based on actual needs, set the maximum number of stations in a single subnet. If the number of stations in a certain area exceeds this limit, the subnetting process will be initiated. The maximum density subnetting method will be used to divide the area into several subnets, so that the stations in each subnet have similar point distribution and density.

[0138] 3) Repeat step 2) until all regions are subnetted.

[0139] 4) Add the same constraint stations in each subnet within the same region to solve the constraints.

[0140] Figure 2 and Figure 3 Schematic diagrams of partitioning and meshing are shown respectively. This partitioning and meshing method, considering the large number, wide distribution, and uneven density of reference frame base stations, can optimize the mesh structure and improve solution accuracy.

[0141] After dividing the region into subnets, a double-difference network solution is performed for each subnet within each region. The double-difference network solution can generally be performed using high-precision solution software such as Bernese or GAMIT / GLOBK, which will not be elaborated here.

[0142] Step 3: Use the multivariate robust normal equation superposition algorithm to merge the subnet single-day solutions.

[0143] Step two above yields the single-day solution for each subnet. Next, all the single-day solutions for each subnet need to be merged to obtain the overall single-day solution for all base stations in the self-built reference frame. The specific algorithm is as follows:

[0144] For ease of discussion, assume that the unknowns in the single-day solutions for all n subnets are X. The error equation for the single-day solution of the i-th subnet is:

[0145] V i =B i Xl i (2)

[0146] Error equations for stacking single-day solutions for all subnets:

[0147]

[0148] X can be solved using least squares, and the weight matrix of the single-day solution for each subnet is denoted as P. i Then the normal equation for the solution of the entire network in a single day is:

[0149] Nx=b (4)

[0150] in,

[0151]

[0152]

[0153] To constrain the results of the single-day solution for the entire network to a specific frame, it is also necessary to introduce the coordinates of the frame points for minimum constraints. Let the coordinates of the frame points in the same epoch be X. R Let X be the estimated value of the constrained adjustment. c According to Helmert transformation relationships:

[0154] X R =X c +Aθ (7)

[0155] In the above formula, θ represents the seven parameters of the frame transformation, and A is the design matrix. Using least squares, we can obtain:

[0156] θ=(A T A) -1 A T (X R -X c (8)

[0157] In order to make X R and X c For the same frame, θ needs to be constrained to 0, denoted as E = (A T A) -1 A T Therefore, the observation equation for the constraint is:

[0158] E(X R -X c )=0 (9)

[0159] The normal equation for the above formula is:

[0160] (E T P θ E)(X R -X c )=0 (10)

[0161] Combining equation (4), the normal equation after applying the minimum constraint is:

[0162] (b+E T E)x=b+(E T E)(X R -X c (11)

[0163] The above formula yields the minimum-constraint single-day solution for the entire network, which has high accuracy. However, some base station single-day coordinates remain unstable, or the base stations have undergone unknown relocation or movement. Therefore, the single-day solutions are further used to superimpose and merge the normal equations into a weekly solution. During the merging of weekly solutions, robustness or simple robustness may introduce errors. Therefore, this preferred embodiment improves the robustness algorithm in the normal equation superposition algorithm, specifically including the following steps:

[0164] 1. A base station has n daily coordinates (corresponding to weekly coordinates, where n is 7). These n coordinates are sorted, and the difference dx1 between the maximum value xmax and the minimum value xmin is calculated. If dx1 exceeds the relocation identification limit, the relocation judgment logic is entered.

[0165] 2. If a base station enters the relocation judgment logic, its daily coordinates are grouped. If a coordinate value for a given day is close to xmax, its epoch information is assigned to group_index_bigger; conversely, if the coordinate value is close to xmin, its epoch information is assigned to group_index_lesser. The purpose of grouping is to identify, from a chronological perspective, whether it's a relocation (a one-time, significant change in daily coordinates) or simply a disturbance (fluctuations in daily coordinates). If all elements in group_index_bigger are greater than or less than group_index_lesser, the base station is determined to have been relocated or moved. If the number of elements in group_index_bigger is greater than the number of elements in group_index_lesser, only the coordinates corresponding to the epochs in group_index_bigger are retained; otherwise, only the coordinates corresponding to the epochs in group_index_lesser are retained.

[0166] 3. By accurately identifying base station relocation through steps 1 and 2, the following steps use a general gross error detection algorithm to detect gross errors in the remaining single-day coordinates of the base station and remove the identified gross errors.

[0167] 4. After steps 1, 2, and 3, obvious gross errors have been identified and eliminated. The average of the remaining single-day solutions is taken as the unified prior initial value x0, and a threshold dx2 is set again. If the difference between the remaining single-day solutions and x0 exceeds dx2, the single-day solution is discarded during the merging process.

[0168] The aforementioned multi-robust algorithm effectively prevents base station movement or relocation under unknown circumstances.

[0169] As described above, this multi-progressive algorithm consists of three steps: first, identifying any unknown relocations or moves (steps 1 and 2); then, performing general gross error detection (step 3); and finally, further eliminating minor gross errors by judging the difference between the daily solution coordinates and the unified prior value (step 4). Through this multi-progressive processing, the influence of unknown relocations or moves on the weekly solution coordinates can be eliminated, allowing for more accurate identification and elimination of gross errors, thereby improving the accuracy of the weekly solution coordinates and obtaining smooth and stable reference station weekly solution coordinates.

[0170] Step 4: Use weekly solutions to perform high-frequency full updates on the frame coordinates to maintain the frame's dynamism.

[0171] To ensure the dynamic nature of the frame, coordinate frames like ITRF maintain it using linear velocity. Coordinates at any epoch can be derived from reference epoch coordinates and velocity values. However, station movement involves not only linear motion but also many periodic movements. Furthermore, factors such as earthquakes and equipment replacement can cause step changes in station coordinates. Therefore, the real-time coordinates obtained by using reference epoch coordinates + velocity derivation are not accurate. We employ a high-frequency full update + partial update approach to maintain the real-time nature of the reference frame, as detailed below:

[0172] Determine a reasonable time interval A, such as 1 month or 2 months. Release a new weekly coordinate version of the framework's full set of base stations every time this time interval is reached. Simultaneously, set a smaller time interval B, such as 7 days or 14 days, and a coordinate change limit dX. After releasing the weekly coordinate version of the full set of base stations, every time time interval B is reached, check if there is a base station coordinate difference greater than dX between the latest real-time weekly report and the released weekly report. If so, release a minor version to modify the base stations whose coordinate changes exceed the limit, until time interval A is reached again, at which point a new weekly coordinate version of the full set of base stations is released.

[0173] Figure 7 This is a schematic diagram of a coordinate reference frame for high-frequency full and partial updates of base station coordinates.

[0174] The high-frequency update scheme for the coordinate frame's base station coordinates maintains the real-time performance of the coordinate reference frame and eliminates the adverse effects of periodic motion and non-structural factors on the frame.

[0175] In addition, to ensure that the base station coordinates of the reference frame can be calculated to different epochs, this technical solution also provides a velocity field model.

[0176] In summary, the technical solution of this preferred embodiment can achieve the following technical effects:

[0177] 1. SSR and OSR services have different requirements for the density and distribution of reference stations. To simultaneously satisfy these two location enhancement services, the reference frame will have the following characteristics: reference stations are globally distributed to provide data and benchmarks for SSR service solutions; reference stations are densely distributed in certain regions to provide data and benchmarks for OSR service solutions in the corresponding regions. This scheme ensures high-precision double-difference network solutions for globally covered, complexly distributed, numerous, and varying densities of base stations through reasonable partitioning, network division, and merging algorithms.

[0178] 2. Gross errors are identified using coordinate time series and a method based on the superposition of normal equations is used to generate the weekly solution of the reference station, making the coordinates of the frame reference station smoother and more stable.

[0179] 3. By updating the coordinates of the high-frequency full-scale reference station, the real-time and dynamic nature of the coordinate reference frame is ensured. A velocity field model is also provided to enable coordinate epoch calculation.

[0180] All embodiments of the present invention can be implemented in software, hardware, firmware, etc. Regardless of whether the present invention is implemented in software, hardware, or firmware, the instruction code can be stored in any type of computer-accessible memory (e.g., permanent or modifiable, volatile or non-volatile, solid-state or non-solid-state, fixed or replaceable media, etc.). Similarly, the memory can be, for example, Programmable Array Logic (PAL), Random Access Memory (RAM), Programmable Read Only Memory (PROM), Read-Only Memory (ROM), Electrically Erasable Programmable ROM (EEPROM), magnetic disk, optical disk, Digital Versatile Disc (DVD), etc.

[0181] The second embodiment of this application relates to a device for calculating and maintaining a GNSS coordinate reference frame. Figure 8 This is a schematic diagram of the GNSS coordinate reference frame calculation and maintenance device.

[0182] Specifically, such as Figure 8 As shown, the GNSS coordinate reference frame calculation and maintenance device includes:

[0183] The selection module is used to select a portion of ITRF stations and combine them with the reference stations to be calculated to form the coordinate reference frame; wherein, the ITRF stations are used to fix the coordinate reference frame;

[0184] The sub-region module is used to divide the area covered by the coordinate reference frame into several regions, and then divide each region into several sub-networks. In each sub-network within the same region, the same ITRF station is included as a constraint station for frame constraint.

[0185] The subnet single-day solution coordinate calculation module is used to perform double-difference network solution for each subnet under the framework constraints to obtain the subnet single-day solution coordinates for each subnet.

[0186] The whole network single-day solution coordinate calculation module is used to merge the subnet single-day solution coordinates of each subnet to obtain the whole network single-day solution coordinates;

[0187] The weekly coordinate calculation module is used to merge the daily coordinates of the entire network for seven days in a week to obtain the weekly coordinates of the base station of the coordinate reference frame.

[0188] This embodiment is a device embodiment corresponding to the first embodiment, and this embodiment can be implemented in conjunction with the first embodiment. The relevant technical details mentioned in the first embodiment remain valid in this embodiment, and will not be repeated here to avoid repetition. Correspondingly, the relevant technical details mentioned in this embodiment can also be applied to the first embodiment.

[0189] It should be noted that the modules mentioned in the above-described device embodiments of this application are all logical modules. Physically, a logical module can be a physical module, a part of a physical module, or a combination of multiple physical modules. The physical implementation of these logical modules is not the most important factor; rather, the combination of functions implemented by these logical modules is the key to solving the technical problem proposed by this invention. Furthermore, to highlight the innovative aspects of this invention, the above-described device embodiments of this invention have not introduced modules that are not closely related to solving the technical problem proposed by this invention. This does not mean that the above-described device embodiments do not contain other modules.

[0190] It should be noted that those skilled in the art should understand that the functions of each module shown in the above-described device embodiments can be understood with reference to the relevant descriptions of the corresponding methods. The functions of each module shown in the above-described device embodiments can be implemented by a program (executable instructions) running on a processor, or by specific logic circuits. If the above-described devices in the embodiments of this specification are implemented as software functional modules and sold or used as independent products, they can also be stored in a computer-readable storage medium. Based on this understanding, the technical solutions of the embodiments of this specification, in essence or in terms of contributing to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the methods described in the various embodiments of this specification. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), magnetic disks, or optical disks. Thus, the embodiments of this specification are not limited to any specific hardware and software combination.

[0191] It should be noted that in this patent application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one" does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. In this patent application, if it refers to performing an action according to an element, it means performing the action at least according to that element, including two cases: performing the action only according to that element, and performing the action according to that element and other elements. Expressions such as "multiple," "repeatedly," and "various" include two, two times, two kinds, and more than two, more than two times, and more than two kinds.

[0192] Although this application has been illustrated and described with reference to certain preferred embodiments thereof, those skilled in the art should understand that various changes in form and detail may be made thereto without departing from the spirit and scope of this application.

Claims

1. A method for solving and maintaining a GNSS coordinate reference frame, characterized in that, Includes the following steps: Select a portion of ITRF stations and combine them with the reference stations to be calculated to form the coordinate reference frame; wherein, the ITRF stations are used to fix the coordinate reference frame; The area covered by the coordinate reference frame is divided into several regions, and each region is further divided into several subnets. Each subnet within the same region includes the same ITRF station as a constraint station for frame constraint. Under the framework constraints, the double-difference network solution is performed on each subnet to obtain the subnet single-day solution coordinates for each subnet; The single-day solution coordinates of each subnet are merged to obtain the single-day solution coordinates of the entire network; The coordinates of the entire network on a single day for seven days of the week are merged to obtain the weekly coordinates of the base station of the coordinate reference frame. The step of merging the single-day coordinates of the entire network for seven days to obtain the weekly coordinates of the reference station of the coordinate reference frame includes the following sub-steps: Based on time series analysis, the robust daily solution coordinates of the entire network are merged into weekly solution coordinates using a normal equation superposition algorithm. The step of performing robust analysis based on time series data and merging the robust daily solution coordinates of the entire network into weekly solution coordinates using a normal equation superposition algorithm includes the following sub-steps: Obtain the daily solution for each base station from the daily solution of the whole network, sort the daily solution coordinates of each base station for seven days of the week in chronological order, and determine whether the difference between the maximum and minimum values ​​of the daily solution coordinates for seven days of the week is greater than the relocation identification threshold. If so, the daily solution coordinates of the base station for seven days of the week are grouped, the epoch information of the daily solution coordinates that are close to the maximum value are assigned to the first group, the epoch information of the daily solution coordinates that are close to the minimum value are assigned to the second group, and it is determined whether all the epoch information in the first group is greater than or less than all the epoch information in the second group. If so, it is determined that the base station has changed position, and it is further determined whether the number of epoch information in the first group is greater than the number of epoch information in the second group; If the number of epochs in the first group is greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the first group; if the number of epochs in the first group is not greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the second group. Gross errors are detected in the retained single-day solution coordinates, and the detected gross errors are removed. The mean of the remaining single-day solution coordinates after removing outliers is used as the initial a priori value. It is then determined whether the difference between each remaining single-day solution coordinate and the initial a priori value is greater than a second threshold. If it is greater than the second threshold, the single-day solution coordinate is discarded; if it is not greater than the second threshold, the single-day solution coordinate is retained. The daily coordinates retained within the seven days of the week are merged to obtain the weekly coordinates of the base station.

2. The method for solving and maintaining the GNSS coordinate reference frame according to claim 1, characterized in that, The step of dividing the area covered by the coordinate reference frame into several regions, and then dividing each region into several subnets, includes the following sub-steps: The area covered by the coordinate reference frame is divided into several regions, and it is determined whether the distribution of reference stations in each region is uniform. Regions with uneven distribution of reference stations are further divided until the reference stations in each region are evenly distributed. Determine whether the number of reference stations in each region is greater than the first threshold. If so, divide the region into several subnets using the maximum density subnetting method.

3. The method for solving and maintaining the GNSS coordinate reference frame according to claim 1, characterized in that, The step of dividing the area covered by the coordinate reference frame into several regions includes the following sub-steps: Based on the site distance clustering partitioning method or the segmentation method, the area covered by the coordinate reference frame is divided into several regions.

4. The method for solving and maintaining the GNSS coordinate reference frame according to claim 1, characterized in that, The step of merging the single-day solution coordinates of each subnet to obtain the single-day solution coordinates of the entire network includes the following sub-steps: The subnet single-day solution coordinates are merged into the whole network single-day solution coordinates using the normal equation superposition algorithm.

5. The method for solving and maintaining the GNSS coordinate reference frame according to claim 1, characterized in that, It also includes the following steps: The coordinates of the coordinate reference frame are updated using the aforementioned Zhou Jie coordinates.

6. The method for solving and maintaining the GNSS coordinate reference frame according to claim 5, characterized in that, The step of updating the coordinates of the coordinate reference frame using the Zhou Jie coordinates includes the following sub-steps: Every first time interval, the coordinates of the coordinate reference frame are updated using the weekly coordinates of all the reference stations of the coordinate reference frame. Within the first time interval, every second time interval, the weekly coordinates of the base stations whose weekly coordinate changes exceed the third threshold are updated in real time; wherein, the first time interval is longer than the second time interval.

7. The method for solving and maintaining the GNSS coordinate reference frame according to claim 1, characterized in that, The step of selecting a portion of ITRF stations includes the following sub-steps: Select ITRF stations whose distribution range covers the coordinate reference frame, and whose coordinate position residuals are less than 5 mm and velocity residuals are less than 3 mm / year.

8. A device for solving and maintaining a GNSS coordinate reference frame, characterized in that, include: The selection module is used to select a portion of ITRF stations and combine them with the reference stations to be calculated to form the coordinate reference frame; wherein, the ITRF stations are used to fix the coordinate reference frame; The sub-region module is used to divide the area covered by the coordinate reference frame into several regions, and then divide each region into several sub-networks. In each sub-network within the same region, the same ITRF station is included as a constraint station for frame constraint. The subnet single-day solution coordinate calculation module is used to perform double-difference network solution for each subnet under the framework constraints to obtain the subnet single-day solution coordinates for each subnet. The whole network single-day solution coordinate calculation module is used to merge the subnet single-day solution coordinates of each subnet to obtain the whole network single-day solution coordinates; The weekly coordinate calculation module is used to merge the single-day coordinates of the entire network for seven days in a week to obtain the weekly coordinates of the base station of the coordinate reference frame. When the weekly coordinate calculation module merges the daily coordinates of the entire network for seven days to obtain the weekly coordinates of the base station of the coordinate reference frame, it performs the following sub-steps: Based on time series analysis, the robust daily solution coordinates of the entire network are merged into weekly solution coordinates using a normal equation superposition algorithm. The step of performing robust analysis based on time series data and merging the robust daily solution coordinates of the entire network into weekly solution coordinates using a normal equation superposition algorithm includes the following sub-steps: Obtain the daily solution for each base station from the daily solution of the whole network, sort the daily solution coordinates of each base station for seven days of the week in chronological order, and determine whether the difference between the maximum and minimum values ​​of the daily solution coordinates for seven days of the week is greater than the relocation identification threshold. If so, the daily solution coordinates of the base station for seven days of the week are grouped, the epoch information of the daily solution coordinates that are close to the maximum value are assigned to the first group, the epoch information of the daily solution coordinates that are close to the minimum value are assigned to the second group, and it is determined whether all the epoch information in the first group is greater than or less than all the epoch information in the second group. If so, it is determined that the base station has changed position, and it is further determined whether the number of epoch information in the first group is greater than the number of epoch information in the second group; If the number of epochs in the first group is greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the first group; if the number of epochs in the first group is not greater than the number of epochs in the second group, then retain the single-day solution coordinates corresponding to the epochs in the second group. Gross errors are detected in the retained single-day solution coordinates, and the detected gross errors are removed. The mean of the remaining single-day solution coordinates after removing outliers is used as the initial a priori value. It is then determined whether the difference between each remaining single-day solution coordinate and the initial a priori value is greater than a second threshold. If it is greater than the second threshold, the single-day solution coordinate is discarded; if it is not greater than the second threshold, the single-day solution coordinate is retained. The daily coordinates retained within the seven days of the week are merged to obtain the weekly coordinates of the base station.

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