A method for plotting land maps based on automatic sorting of unordered boundary points

Abstract

The present invention discloses a plot map drawing method based on automatic sorting of unordered boundary points, comprising: (1) obtaining the coordinates of all boundary points, searching the convex hull sequence of the boundary points by a wrapping method, obtaining a convex hull point sequence C and a non-convex hull scattered point set R; (2) if the set R is an empty set, the plot is a convex polygon structure, the convex hull point sequence C is the only feasible sequence, the convex hull point sequence C is used as the final output sequence, and step (4) is performed; if the set R is a non-empty set, the plot is a concave polygon structure, the points in the set R are traversed with feasible solutions, and a feasible sequence set S is obtained; (3) the angular feature matching probability of all feasible sequences in the set S is calculated, and the sequence with the highest angular feature matching probability is taken as the final output sequence; (4) according to the final output sequence, the boundary points are sequentially connected to complete the drawing of the plot map. The present invention can solve the judgment and composition problems in the scenario where the plot map is a concave polygon.

Description

Technical Field

[0001] The invention belongs to the field of geographic information, and in particular relates to a plot map drawing method based on automatic sorting of disordered boundary points. Background Art

[0002] In the cadastral survey of villages and towns, the characteristics of the plots are usually described by drawing a closed polygonal structure composed of boundary points, namely a plot map. The land use of villages and towns is mainly concentrated in conventional land use scenarios such as residential construction, farming or breeding, so the plot map often presents a relatively simple polygonal structure.

[0003] The survey scope of the cadastral survey of villages and towns is large, the density between plots is not high, and the geometric topological structure of the plots has certain rules. If the plot map is drawn by manual field measurement, or after taking orthographic images, manual puncture points are performed to determine the connection order of boundary points to draw the plot map, there will be problems such as waste of manpower and low accuracy; if electronic boundary points are formed by implanting RFID chips at boundary points, the precise coordinates of the electronic boundary points can be automatically obtained through the chip signal strength, but the connection order of the boundary points cannot be determined. The existing automatic sorting method is only applicable to simple scenarios where the plots are convex polygons. Therefore, the connection order of electronic boundary points still needs to rely on manual field surveys or combined with satellite images to determine, which is inefficient.

[0004] The Chinese patent document with publication number CN101593454A discloses a method for intelligently outputting a plot map based on GIS technology. The method automatically extracts the required information from the standard cadastral database. The user only needs to input the identification code of the plot, such as the plot number or cadastral number, to automatically obtain the plot graphics, and determine the appropriate paper size and scale by calculating its related graphic attributes. However, the method requires that the plot map drawn be stored in the database in advance, and the plot map still needs to be drawn by manual field measurement.

[0005] A Chinese patent document with publication number CN109712235A discloses a method for constructing a plot map containing arc segments, comprising the following steps: A. constructing a polygon based on boundary points, obtaining the area of ​​the polygon, and calculating the area of ​​the arc corresponding to the arc segment; B. obtaining the number of arc segments and the chord length of the arc segment by field measurement, and obtaining the area of ​​the arc corresponding to each arc segment based on the chord length ratio of each arc segment as the area ratio coefficient; C. setting the value range of each arc segment radius and arc segment center angle, and using the dichotomy method to construct a transcendental equation model for solving the arc segment radius and arc segment center angle; D. solving the transcendental equation model to obtain the value of each arc segment center angle, and then calculating the radius corresponding to each arc segment; E. drawing the plot map based on the size parameters of the polygon enclosed by the boundary in the original plot map, and the center angle and radius parameters corresponding to each arc segment to be calculated. This method overcomes the defects of the traditional manual mode, such as complex operation, low precision and low efficiency. However, it requires advance knowledge of the plot area information and focuses on the restoration of arc parameters in scenarios where only paper plot maps are available and the arc parameters of the plot are missing. Therefore, the application scenarios have certain limitations.

[0006] In summary, there is an urgent need to design a method to automatically sort the boundary points whose only precise coordinates are known, so as to achieve automatic and high-precision drawing of the land parcel map. Summary of the invention

[0007] The present invention discloses a plot map drawing method based on automatic sorting of disordered boundary points, which can solve the judgment and composition problems in the plot map of concave polygon scenes, does not need satellite images to assist in drawing boundary lines, and overcomes the defects of manpower waste and low efficiency.

[0008] A method for drawing a land parcel map based on automatic sorting of unordered boundary points comprises the following steps:

[0009] (1) Obtain the coordinates of all boundary points, find the convex hull sequence of the boundary points by the wrapping method, and obtain the convex hull point sequence C and the non-convex hull scattered point set R;

[0010] (2) If the non-convex hull scattered point set R is an empty set, the land parcel is a convex polygon structure, and the convex hull point sequence C is the only feasible sequence. The convex hull point sequence C is used as the final output sequence, and step (4) is executed;

[0011] If the non-convex hull scattered point set R is a non-empty set, then the land parcel is a concave polygon structure. Perform a feasible solution traversal on the points in the set R to obtain a feasible sequence set S, and execute step (3);

[0012] (3) Calculate the corner feature matching probability of all feasible sequences in the feasible sequence set S, and take the sequence with the highest corner feature matching probability as the final output sequence;

[0013] (4) According to the final output sequence, the boundary points are connected in sequence to complete the drawing of the plot map.

[0014] Furthermore, in step (1), the convex hull sequence of boundary points is found by the wrapping method, and the specific process of obtaining the convex hull point sequence C and the non-convex hull scattered point set R is as follows:

[0015] (1-1) Find the point with the smallest y coordinate among all boundary points as the current point; take the horizontal ray pointing to the right as the current ray;

[0016] (1-2) Add the current point to the convex hull point sequence C, connect it with the remaining points, and calculate the angle between each connecting line and the current ray;

[0017] (1-3) Take the other point with the smallest angle as the current point and the corresponding line as the current ray; repeat steps (1-2) until the current point returns to the first sequence point;

[0018] (1-4) The final convex hull point sequence C is obtained, and the remaining points not added to the convex hull point sequence C are counted into the non-convex hull scattered point set R.

[0019] In step (1-1), if there are two points with the same y coordinate, the point with the smaller x coordinate is taken as the current point.

[0020] In step (2), the specific process of traversing the feasible solutions of the points in the set R to obtain the feasible sequence set S is as follows:

[0021] (2-1) Take a point pi in the set R and connect it with the remaining n-1 boundary points to form multiple directed line segments starting from point pi; take the line segment from pi to the lowest point as the main direction and calculate the counterclockwise angle between each line segment and the main direction; establish a point sequence C' and add the remaining boundary points other than pi to the sequence C' in the order of the angle from small to large;

[0022] (2-2) After each element in the sequence C', insert pi one by one, and the resulting sequence is included in the feasible sequence set S;

[0023] (2-3) Select other points in the set R and repeat steps (2-1)-(2-2) until all points in the set R are searched and the final feasible sequence set S is obtained.

[0024] In step (2-2), when the obtained sequence is included in the feasible sequence set S, if any duplicate sequence appears, it needs to be deleted.

[0025] In step (3), the formula for the corner feature matching probability of the feasible sequence is:

[0026]

[0027] Among them, P is the matching probability of the angular features of the feasible sequence, n is the number of boundary points, and f(θ) is the probability distribution function of the angle between the two sides of the plot.

[0028] The formula for the probability distribution function f(θ) of the angle between the two sides of the plot is as follows:

[0029]

[0030] Where θ represents the angle between the two sides of the plot, σ1 and σ2 represent the discrete degrees of the angle between the two sides of the local plot at 90° and 180°, respectively, and a and b are the set parameters.

[0031] To ensure the normalization of f(θ), a and b are set to satisfy the conditional constraint of a+b=1.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The method of the present invention is extended on the basis of the wrapping method which is only applicable to convex polygons, and automatically retrieves the possible reflex angles in the boundary points, solving the judgment and composition problems in the scene where the land parcel map is a concave polygon; with the help of the wrapping method and the reflex angle traversal between two points, all the arrangement orders that can be constructed into closed figures for the boundary points are determined, and the corresponding boundary point sorting sequence set is constructed, laying a solid foundation for the subsequent determination of the land parcel map; combined with the statistical distribution law of the angles on both sides of the land parcel, a calculation model for the angular feature matching probability of the boundary point sorting sequence is established accordingly, and the sorting sequence with the highest angular feature matching probability in the sorting sequence set is the boundary point sorting result that best conforms to the land parcel map law. The present invention has a rigorous principle, is scientific and efficient, does not require satellite images to assist in depicting boundary lines, overcomes the defects of manpower waste and low efficiency, and has excellent social and economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of a plot map drawing method based on automatic sorting of unordered boundary points of the present invention;

[0035] Figure 2 A schematic diagram of searching for non-convex hull scattered points by a roll wrapping method in an embodiment of the present invention;

[0036] Figure 3 A schematic diagram of obtaining sequence C' in an embodiment of the present invention;

[0037] Figure 4 A schematic diagram of obtaining a feasible sequence in an embodiment of the present invention;

[0038] Figure 5 Schematic diagram of summarizing a feasible sequence set S in an embodiment of the present invention;

[0039] Figure 6This is a frequency distribution diagram of the angles between two adjacent sides of six village plots in an embodiment of the present invention. DETAILED DESCRIPTION

[0040] The present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be pointed out that the embodiments described below are intended to facilitate the understanding of the present invention and do not have any limiting effect on the present invention.

[0041] like Figure 1 As shown, a method for drawing a land parcel map based on automatic sorting of unordered boundary points comprises the following steps:

[0042] Step 1, obtain the coordinates of all boundary points, find the convex hull sequence of the boundary points through the wrapping method, and obtain the convex hull point sequence C and the non-convex hull scattered point set R.

[0043] like Figure 2 As shown in the figure, the process of finding the convex hull sequence of boundary points by the wrapping method is:

[0044] Step 1-1, establish a convex hull point sequence C and a non-convex hull scattered point set R.

[0045] Step 1-2, find the point with the smallest y coordinate among the scattered points (if there are two points with the same y coordinates, take the point with the smaller x coordinate) as the current point; use the horizontal ray to the right as the current ray.

[0046] Step 1-3, add the current point to the convex hull point sequence C, connect it with the remaining points, and calculate the angle between each connecting line and the current ray.

[0047] Steps 1-4: Take the other point with the smallest angle between the lines as the current point and the corresponding line as the current ray. Repeat step (3) until the current point returns to the first sequence point.

[0048] In steps 1-5, the remaining points not added to C are counted into the non-convex hull scattered point set R.

[0049] Step 2: If the non-convex hull scattered point set R is an empty set, then the land parcel is a convex polygon structure, and the convex hull point sequence C is the only feasible sequence. The convex hull point sequence C is used as the final output sequence, and step (4) is executed.

[0050] If the non-convex hull scattered point set R is a non-empty set, then the land parcel is a concave polygon structure. Perform a feasible solution traversal on the points in the set R to obtain a feasible sequence set S, and execute step (3).

[0051] Specifically, the construction process of the feasible sequence set S is as follows: Figure 3 to Figure 5 As shown, including:

[0052] Step 2-1, take a point pi in the set R, connect it with the remaining n-1 boundary points, and form multiple directed line segments starting from point pi. Take the line segment from pi to the lowest point as the main direction, and calculate the counterclockwise angle between each line segment and the main direction. Establish a point sequence C', and count the remaining non-pi boundary points into the sequence C' in order of angle from small to large.

[0053] Step 2-2, insert pi one by one after each element in the sequence C', and the resulting sequence is counted into the feasible solution set S. If a repeated sequence appears, it needs to be deleted.

[0054] Step 2-3, select other points in set R and repeat steps (1)-(2) until all points in set R are found.

[0055] Step 3: Calculate the corner feature matching probability of all feasible sequences in the feasible sequence set S, and take the sequence with the highest corner feature matching probability as the final output sequence.

[0056] Affected by the characteristics of conventional housing construction, the distribution of the internal angles of the parcel polygons tends to be close to integer multiples of 90°. In order to reduce the calculation and distinction of polygon angles, the internal and external angles will not be distinguished, that is, the angle range of the adjacent two sides is in the range of (0,180°].

[0057] like Figure 3 As shown in the figure, after analyzing the characteristics of the plots of six villages in Zhejiang, Anhui, Fujian and Henan, it was found that the distribution probability of the angles on both sides of the plots showed a bimodal distribution concentrated at 90° and 180°.

[0058] According to the above geometric characteristics analysis, it is found that the probability distribution function f(θ) of the angle between the two sides of the plot can be fitted by weighted addition of the normal distribution with an expected value of 90° and the half-normal distribution with an expected value of 180°, as shown in formula (1):

[0059]

[0060] In order to ensure the normalization of f(θ), parameters a and b are introduced, and the setting must satisfy the condition constraint of a+b=1.

[0061] In summary, the greater the distribution probability of the angle between adjacent vectors in the sequence, the more the topological shape corresponding to the sequence conforms to the actual polygonal geometry of the plot. In order to facilitate the overall judgment of the sequence, the matching probability P of the angle feature of the sorted sequence of n boundary points is defined as shown in formula (2):

[0062]

[0063] According to formula (2), the corner feature matching probability P of each feasible sequence is calculated, and the sequence with the highest corner feature matching probability P is taken as the final output ranking.

[0064] Step 4: Connect the boundary points in sequence according to the final output sequence to complete the drawing of the plot map.

[0065] The method of the present invention can automatically determine the connection order of n boundary points for the point coordinate information of a certain plot of land to generate the corresponding plot shape. The whole process does not require satellite images to assist in drawing boundary lines, overcomes the defects of manpower waste and low efficiency, and has excellent social and economic value.

[0066] The embodiments described above provide a detailed description of the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements and equivalent substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for plotting a land parcel based on automatic sorting of unordered boundary points, characterized in that: The following steps are involved: (1) Obtain the coordinates of all boundary points, find the convex hull sequence of the boundary points by the wrapping method, and obtain the convex hull point sequence C and the non-convex hull scattered point set R; (2) If the non-convex hull scattered point set R is an empty set, the land parcel is a convex polygon structure, and the convex hull point sequence C is the only feasible sequence. The convex hull point sequence C is used as the final output sequence, and step (4) is executed; If the non-convex hull scattered point set R is a non-empty set, then the land parcel is a concave polygon structure. Perform a feasible solution traversal on the points in the set R to obtain a feasible sequence set S, and execute step (3); (3) Calculate the corner feature matching probability of all feasible sequences in the feasible sequence set S, and take the sequence with the highest corner feature matching probability as the final output sequence; the formula for the corner feature matching probability of a feasible sequence is: Among them, P is the matching probability of the angular features of the feasible sequence, n is the number of boundary points, and f(θ) is the probability distribution function of the angle between the two sides of the plot; The formula for the probability distribution function f(θ) of the angle between the two sides of the plot is as follows: In the formula, θ represents the angle between the two sides of the plot, σ1 and σ2 represent the discrete degrees of the angle between the two sides of the local plot at 90° and 180° respectively, and a and b are set parameters; to ensure the normalization of f(θ), a and b are set to satisfy the conditional constraint of a+b=1; (4) According to the final output sequence, the boundary points are connected in sequence to complete the drawing of the plot map.

2. The method for drawing a land parcel map based on automatic sorting of unordered boundary points according to claim 1, characterized in that: In step (1), the convex hull sequence of boundary points is found by the wrapping method, and the specific process of obtaining the convex hull point sequence C and the non-convex hull scattered point set R is as follows: (1-1) Find the point with the smallest y coordinate among all boundary points as the current point; take the horizontal ray pointing to the right as the current ray; (1-2) Add the current point to the convex hull point sequence C, connect it with the remaining points, and calculate the angle between each connecting line and the current ray; (1-3) Take the other point with the smallest angle as the current point and the corresponding line as the current ray; repeat steps (1-2) until the current point returns to the first sequence point; (1-4) The final convex hull point sequence C is obtained, and the remaining points not added to the convex hull point sequence C are counted into the non-convex hull scattered point set R.

3. The method for drawing a land parcel map based on automatic sorting of unordered boundary points according to claim 2, characterized in that: In step (1-1), if there are two points with the same y coordinate, the point with the smaller x coordinate is taken as the current point.

4. The method for drawing a land parcel map based on automatic sorting of unordered boundary points according to claim 1, characterized in that: In step (2), the specific process of traversing the feasible solutions of the points in the set R to obtain the feasible sequence set S is as follows: (2-1) Take a point pi in the set R and connect it with the remaining n-1 boundary points to form multiple directed line segments starting from point pi; take the line segment from pi to the lowest point as the main direction and calculate the counterclockwise angle between each line segment and the main direction; establish a point sequence C' and add the remaining boundary points other than pi to the sequence C' in the order of the angle from small to large; (2-2) After each element in the sequence C', insert pi one by one, and the resulting sequence is included in the feasible sequence set S; (2-3) Select other points in the set R and repeat steps (2-1)-(2-2) until all points in the set R are searched and the final feasible sequence set S is obtained.

5. The method for drawing a land parcel map based on automatic sorting of unordered boundary points according to claim 4, characterized in that: In step (2-2), when the obtained sequence is included in the feasible sequence set S, if any duplicate sequence appears, it needs to be deleted.

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