Partition quasi-geoid fitting method based on overrun verification point distribution condition

Abstract

The invention provides a subarea quasi-geoid fitting method based on an overrun verification point distribution condition. The subarea quasi-geoid fitting method comprises the following steps: collecting research area data; constructing a gravity quasi-geoid according to the data of the research area; performing overall fitting on the data of the gravity quasi-geoid by using the data of the research area to generate a quasi-geoid; setting an interval range of the verification points, wherein the verification points exceeding the range are over-limit verification points; segmenting a region with a relatively large error after overall fitting, and performing region fitting on the region; if an over-limit verification point exists after region fitting, carrying out zoning again according to topographic factors and carrying out topographic fitting; generating a new geoid according to a fitting result; according to the invention, the gravity data is combined with the DEM data and the ground field model to construct the gravity quasi-geoid; according to the method, a region with a large error after fitting can be segmented, and re-fitting is performed according to topographic factors, so that the error caused by fitting is reduced, and the precision of the geoid is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of environmental surveying and mapping, and particularly relates to a method for fitting a regional quasi-geoid based on the distribution of over-limit verification points. Background Art

[0002] The geoid is an important basic surface for describing the Earth's gravity field and is widely used in the fields of surveying and mapping, earth science, and engineering. Its accurate description is of great significance for the determination of high-precision elevation benchmarks, the elevation calculation of satellite positioning systems (such as GPS), and the monitoring of terrain changes. However, due to the complex shape of the Earth's surface and the non-uniform distribution of the gravity field, traditional geoid models often fail to meet the accuracy requirements of modern surveying and mapping projects. Therefore, the refinement research of the geoid has become one of the core topics in the academic and engineering fields.

[0003] In recent years, with the development of global navigation satellite system (GNSS) technology, the improvement of high-precision gravity measurement methods, and the popularization of digital elevation models (DEMs), more reliable data sources and technical tools have been provided to improve the accuracy of the geoid.

[0004] However, in practical applications, in the process of fitting the gravity quasi-geoid and the GPS / leveling points to the quasi-geoid, usually in complex terrain areas, affected by the high-frequency information in factors such as terrain, the fitting effect in some areas is not good enough, thus affecting the accuracy of the entire quasi-geoid. Summary of the Invention

[0005] To solve the above problems, the technical solution of the present invention is as follows:

[0006] A method for fitting a regional quasi-geoid based on the distribution of over-limit verification points, comprising the following steps:

[0007] Collect data of the study area: Collect gravity data, DEM data, high-resolution Earth gravity field data, and GPS / leveling data of the study area;

[0008] Construct a gravity quasi-geoid based on the data of the study area;

[0009] Perform overall fitting on the data of the gravity quasi-geoid using the data of the study area to generate a quasi-geoid;

[0010] Set the interval range of verification points: Set the error range between the verification points and the fitting result, and the verification points exceeding the range are over-limit verification points;

[0011] Divide the area with larger errors after overall fitting, and perform regional fitting on the area; if there are over-limit verification points after regional fitting, re-divide according to terrain factors and perform terrain fitting;

[0012] Generate a new quasi-geoid according to the fitting result.

[0013] Furthermore, construct a gravity quasi-geoid by combining gravity data with DEM data and the Earth's field model to construct a gravity quasi-geoid.

[0014] Furthermore, use the data of the study area to globally fit the data of the gravity quasi-geoid. Based on GPS / levelling data, among the levelling points in the study area, select evenly distributed points as fitting points for the parameters of the fitting calculation, and the remaining points as verification points to check the accuracy of the fitting result, and globally fit the data of the gravity quasi-geoid.

[0015] Furthermore, the steps for dividing the area with large errors after global fitting include the following:

[0016] Mark all the over-limit and non-over-limit verification points in the study area;

[0017] According to the distribution of the over-limit verification points, divide the adjacent verification points into zones using rectangles or ellipses, and the zones contain non-over-limit verification points and fitting points; if a certain area contains only one over-limit verification point, divide this area into a separate area and divide it using a rectangle or a circle so that there are more than 3 non-over-limit verification points and more than 5 fitting points inside the area.

[0018] Among them, regional fitting means that in the divided areas, the non-over-limit verification points are still used as verification points, and the remaining fitting points and over-limit verification points are used as fitting points for regional fitting.

[0019] Furthermore, re-zone according to topographic factors, with the original over-limit verification point as the center, draw an area according to the terrain undulation obtained from the collected data, which does not include the original non-over-limit verification points.

[0020] Among them, drawing an area according to the terrain undulation means enclosing the entire terrain along the contour line according to the terrain undulation at the position of the over-limit points; terrain fitting means using the over-limit verification points in the regional fitting as fitting points, and among the remaining levelling points in the area, evenly distributed levelling points as fitting points, and the remaining as verification points for fitting.

[0021] Furthermore, generate a new quasi-geoid by replacing the results of each area after global fitting with the results of internal fitting of each area.

[0022] The present invention has the following beneficial effects:

[0023] 1) Construct a gravity quasi-geoid by combining gravity data with DEM data and the Earth's field model;

[0024] 2) In the case where the gravity quasi-geoid has been constructed, the areas with large fitting errors can be segmented, and refitted according to topographic factors again to reduce the errors caused by fitting and improve the accuracy of the quasi-geoid. Description of the Drawings

[0025] Figure 1 It is a flowchart provided by an embodiment of the present invention;

[0026] Figure 2 It is an overall fitting segmentation diagram of test cases provided by an embodiment of the present invention;

[0027] Figure 3 It is a diagram of the re-fitting area division of test cases provided by an embodiment of the present invention. Detailed Embodiments

[0028] The following makes a detailed description of the specific embodiments of the present invention in conjunction with the drawings.

[0029] Embodiment 1

[0030] A method for fitting a zonal quasi-geoid based on the distribution of over-limit verification points, as Figure 1 shown, includes the following steps:

[0031] S1. Collect data of the study area: Collect gravity data, DEM data, high-resolution earth gravity field data, and GPS / levelling data of the study area. The GPS / levelling data includes level points, and the level points are reference points used to transfer elevation in elevation control surveys. It is the point whose elevation is measured by the levelling method.

[0032] Furthermore, constructing the gravity quasi-geoid is to construct the gravity quasi-geoid by combining gravity data with DEM data and the earth field model.

[0033] S2. Construct the gravity quasi-geoid according to the data of the study area.

[0034] In this step, constructing the gravity quasi-geoid is to construct the gravity quasi-geoid by combining gravity data with DEM data and the earth field model.

[0035] S3. Use the data of the study area to perform overall fitting on the data of the gravity quasi-geoid to generate a quasi-geoid.

[0036] Among them, using the data of the study area to perform overall fitting on the data of the gravity quasi-geoid is based on the GPS / levelling data. Among the level points in the study area, points with uniform distribution are selected as fitting points for the parameters used in the fitting calculation, and the remaining ones are used as verification points to check the accuracy of the fitting result, and overall fitting is performed on the data of the gravity quasi-geoid. The fitting result generates a quasi-geoid.

[0037] The fitting method can select fitting methods with a certain degree of accuracy such as polynomial fitting or BP neural network fitting.

[0038] S4. Set the interval range of the verification points: Set the error range between the verification points and the fitting result, and the verification points outside the range are over-limit verification points.

[0039] S5. Divide the area with a large error after overall fitting, and perform regional fitting for the said area; if there are over-limit verification points after regional fitting, then perform S51.

[0040] In this step, dividing the area with a large error after overall fitting includes the following steps:

[0041] Mark all over-limit and non-over-limit verification points in the study area.

[0042] According to the distribution of the over-limit verification points, partition the adjacent verification points using rectangles or ellipses. The said partitions contain non-over-limit verification points and fitting points; if a certain area contains only one over-limit verification point, then divide this area into a separate area and perform segmentation using a rectangle or a circle so that there are more than 3 non-over-limit verification points and more than 5 fitting points inside the area.

[0043] Among them, regional fitting means that among the divided areas, the non-over-limit verification points continue to be regarded as verification points, and the remaining fitting points and over-limit verification points are used as fitting points for regional fitting; as Figure 2 shown in the overall fitting segmentation diagram of the test case, in the figure, the black rectangle is the study area, X and Y are the coordinate systems of the study area (latitude and longitude can also be used), the black points are fitting points, the blue points are non-over-limit verification points, the red points are over-limit verification points, the purple rectangular frame is the divided study area 1, and the orange frame is the divided study area 2.

[0044] S51. Re-partition according to the terrain factors and perform terrain fitting.

[0045] In this step, re-partitioning according to the terrain factors is to draw an area centered on the original over-limit verification points according to the terrain undulation obtained from the collected data, which does not include the original non-over-limit verification points.

[0046] Among them, drawing an area according to the terrain undulation means enclosing the entire terrain along the contour line according to the terrain undulation at the position of the over-limit points; terrain fitting means using the over-limit verification points in the regional fitting as fitting points, and among the remaining leveling points in the area, the evenly distributed leveling points are used as fitting points, and the rest are used as verification points for fitting; as Figure 3As shown in the re-fitted area division diagram of the test case, the coordinate system on the right side of the diagram is the elevation of this place. The blue points are the verification points that did not exceed the limit during the overall fitting, the red points are the verification points that exceeded the limit during the overall fitting, and the red ellipsoidal frame is the replacement area divided according to the verification points that exceeded the limit.

[0047] S6. Generate a new quasi-geoid according to the fitting result.

[0048] In this step, the new quasi-geoid is generated by replacing the results of each area after overall fitting with the results of fitting within each area. The elevation anomalies of the points in each area are replaced by the results obtained by re-fitting the points in the area again according to the partition, generating a new quasi-geoid of the study area. Since the areas with low fitting accuracy around the original verification points that exceeded the limit are replaced by the points in the re-fitted area, the accuracy of the quasi-geoid after fitting in the entire study area can be effectively improved.

[0049] Through the present invention, it is possible to construct a gravity quasi-geoid by using gravity data in combination with DEM data and the earth field model; in the case where a gravity quasi-geoid has been constructed, the areas with large errors after fitting can be segmented, and re-fitting can be performed again according to topographic factors to reduce the errors caused by fitting and improve the accuracy of the quasi-geoid.

[0050] The above discloses only several specific embodiments of the present invention. However, the present invention is not limited thereto, and any changes that can be thought of by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for fitting a quasi-geoid based on the distribution of over-limit verification points, characterized in that: The following steps are involved: Collect data in the study area: including gravity data, DEM data, high-resolution earth gravity field data and GPS / leveling data in the study area; Construct a gravity quasi-geoid based on the data of the study area; The data of the study area are used to perform an overall fit on the data of the gravity quasi-geoid to generate a quasi-geoid. Set the interval range of the verification point: set the error range between the verification point and the fitting result. The verification point beyond the range is the out-of-limit verification point; The area with a large error after the overall fitting is segmented, and regional fitting is performed on the area; if there are over-limit verification points after regional fitting, the area is re-divided according to terrain factors and terrain fitting is performed; Generate a new quasi-geoid based on the fitting results.

2. The partitioned quasi-geoid fitting method according to claim 1, characterized in that: The construction of the gravity quasi-geoid is to construct the gravity quasi-geoid by combining gravity data with DEM data and an earth field model.

3. The partitioned quasi-geoid fitting method according to claim 1, characterized in that: The overall fitting of the gravity quasi-geoid data using the study area data is based on GPS / leveling data. Among the leveling points in the study area, evenly distributed points are selected as fitting points for fitting calculation parameters, and the rest are used as verification points to test the accuracy of the fitting results, and the overall fitting of the gravity quasi-geoid data is performed.

4. The partitioned quasi-geoid fitting method according to claim 1, characterized in that: The segmentation of the region with a large error after the overall fitting comprises the following steps: Mark all the over-limit and under-limit verification points in the study area; According to the distribution of the verification points that exceed the limit, the adjacent verification points are partitioned into rectangles or ellipses, and the partitions contain the verification points and fitting points that are not exceeded. If an area contains only one verification point that exceeds the limit, this area is divided into a separate area and partitioned into rectangles or circles so that the area contains more than 3 verification points that are not exceeded and more than 5 fitting points.

5. The method for fitting a sub-regional quasi-geoid according to claim 4, characterized in that: The regional fitting is to divide the areas into several regions, and continue to use the verification points that do not exceed the limit as verification points, and use the remaining fitting points and the verification points that exceed the limit as fitting points to perform regional fitting.

6. The partitioned quasi-geoid fitting method according to claim 1, characterized in that: The rezoning according to terrain factors is to draw an area with the original over-limit verification point as the center according to the terrain undulations obtained from the collected data, which does not include the original non-over-limit verification point.

7. The method for fitting a sub-regional quasi-geoid according to claim 6, characterized in that: The method of drawing an area according to the terrain undulation is to circle the entire terrain along the contour lines according to the terrain undulation at the position of the over-limit point.

8. The method for fitting a sub-regional quasi-geoid according to claim 6, characterized in that: The terrain fitting is to use the verification points that exceed the limit in the regional fitting as fitting points, and the evenly distributed leveling points among the remaining leveling points in the area as fitting points, and the rest as verification points for fitting.

9. The partitioned quasi-geoid fitting method according to claim 1, characterized in that: The generation of a new quasi-geoid is to replace the results of each region after overall fitting with the results of internal fitting in each region.

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