CN104766081A - Method for extracting territorial sea baseline based on natural coastline data - Google Patents

Abstract

A method for extracting territorial sea baselines based on natural coastline data, mainly including the natural coastline thinning method based on the improved Douglas-Pucker algorithm and the territorial sea baseline encryption algorithm based on the geodetic calculation of the earth ellipsoid, in order to delineate the territorial sea baseline Certainly. In the process of thinning, the present invention extracts the natural coastline salient points that have a greater impact on the sea area as segmentation points, and then uses adjacent segmentation points as data to thin out the first and last points, and selects them with a fitting curve based on the least squares method The optimal distance threshold is thinned out segment by segment, which can protect the national ocean rights and interests while ensuring high accuracy and compression rate. In the encryption algorithm, the algorithm is based on the calculation of the geodetic line on the ellipsoidal surface of the earth, and the geodetic line is fitted between the adjacent territorial sea base points, and then the encryption calculation is performed between the adjacent base points by using the geodetic theme calculation principle. During the calculation process, the distance judgment conditions and the positions of encrypted points are improved, the calculation speed is improved, and the position distribution of the territorial sea base points is more reasonable.

Description

Method of Extracting Territorial Sea Baseline Based on Natural Coastline Data

technical field

The present invention relates to a method for determining territorial sea base points and defining territorial sea baselines, specifically, to a method of thinning natural coastlines and encrypting territorial sea base points to generate territorial sea baselines, providing assistance for demarcating sea areas and effectively safeguarding my country's marine rights and interests. Technical Support.

Background technique

The 21st century is the century of the ocean. The ocean contains rich resources such as oil and gas, fishery, and minerals. While promoting the rapid development of the national economy, it has also become the focus of competition among countries. Significant. The determination of territorial sea base points and the delineation of territorial sea baselines have long-term strategic significance and great practical significance for safeguarding my country's maritime rights and interests, consolidating coastal defense construction, protecting the marine environment, and strengthening marine management.

The baseline of the territorial sea is the starting line used by the coastal state to measure the outer limit of the territorial sea and certain other outer limits of the jurisdiction of the territorial sea state, and the sea area extending to the ocean to a certain width is the territorial sea. According to the provisions of the United Nations Convention on the Law of the Sea (hereinafter referred to as the "Convention"), territorial sea baselines are divided into three types: normal baselines, straight baselines, and mixed baselines. The normal baseline is the low tide line when the sea water ebbs along the coast of the mainland and around the islands; the straight baseline is the selected base points at the protruding part of the coast of the mainland and the most foreign aid of the coastal islands, and then connect the adjacent base points with a straight line The resulting polyline; a mixed baseline, that is, a normal baseline and a straight baseline are used alternately.

Knowing the natural coastline, if the normal baseline is used to extrapolate the territorial sea line, the speed of further calculation will be affected or the calculation will be seriously complicated due to the high density of initial data points. In order to simplify, the coastline feature points can be selected according to a certain density (that is, thinning) to form a "direction line" instead of the natural coastline for extrapolation. At present, there is no mature algorithm for generating direction lines from natural coastline thinning. However, the general curve compression theory is very mature, including interval point method, angle limit method, grating method, vertical distance limit method, Douglas-Puke method, etc. Among them, the Douglas-Pocke algorithm is the most classic thinning method. The algorithm is simple to implement, high in efficiency, and has a good simplification effect.

The Douglas-Puke algorithm thins out the entire curve. Its basic idea is: set the distance threshold, and then connect the first and last points of the curve to form a straight line; calculate the distance between the middle points and the straight line, and find the maximum distance and the maximum distance point ; If it is less than the threshold, replace the original curve with this straight line, if it is greater than the threshold, divide the line segment into two segments at this point; repeat the above process for these two segments, and the last retained point is the result of data compression. The Douglas-Pocke algorithm is a thinning method from the whole to the local, the compression curve has little deviation from the original curve and the compression rate is high. The degree of compression and precision depends on the threshold. The larger the threshold, the greater the compression rate, but the lower the precision; the smaller the threshold, the smaller the compression rate, and the higher the precision.

Although the thinning effect of the Douglas-Pocke algorithm is better than that of other algorithms, there are still some defects: some important feature points may be discarded; self-intersection phenomenon is easy to occur when the line type is complex or the threshold is large; The common boundary compression of linear targets is inconsistent; topological inconsistency leads to terrain distortion, etc.

Given the territorial sea baseline, too far distance between adjacent points will affect calculation accuracy and accurate drawing. In the case of using a straight baseline, international mainstream scholars suggest that the distance between adjacent territorial sea base points should not exceed 24 nautical miles. Therefore, interpolation (that is, encryption) is required for adjacent base points whose distance is too large.

Contents of the invention

The technical problem to be solved by the present invention is: to overcome the above-mentioned defects of the prior art, and to propose a method for extracting territorial sea baselines based on natural coastline data.

In order to solve the above-mentioned technical problems, the technical solution proposed by the present invention is a method for extracting territorial sea baselines based on natural coastline data, which is characterized in that it includes the following steps:

Step 1. Select salient points—for the natural coastline feature point set N, use the vector cross product formula to select salient points and store them in the point set M;

Step 2. Select segment points—the first and last points in point set N are defaulted as segment points, which are directly stored in segment point set T; and the remaining points in point set M and the two adjacent points in point set N are calculated in turn The area value S of the triangle, if S≥S ₀ , then the point in the point set M is determined as a segment point and stored in the segment point set T, where S ₀ is the preset area threshold;

Step 3. Determine the optimal distance threshold D for each segment——for the natural coastline feature point set between adjacent segment points, select the optimal distance threshold D;

Step 4. Segmented data thinning—Using segment points to divide the natural coastline into several segmented coastlines, using two adjacent segment points as the first and last points of the segmented coastline, and using the optimal distance threshold D as the initial For the distance threshold, the Douglas-Puck algorithm is used to extract the data of the natural coastline in sections, and several alternative base points are obtained, and the connection lines of the alternative base points form the direction line;

Step 5. Adjustment of the distance threshold - fine-tuning the distance threshold of the segmented coastline to balance the sea area and thinning accuracy, and obtain the corrected alternative base point and the corrected direction line;

Step 6. Acquisition of territorial sea base points - according to the United Nations Convention on the Law of the Sea, obtain the coastal base points according to the revised alternative base points;

Step 7. Territorial sea base point encryption - for the geodetic length L between any two adjacent territorial sea base points, if it is greater than the preset encryption distance s, then increase [L/S ] encryption points, so that the geodetic length between adjacent points does not exceed the encryption distance s; where the operator [ ] represents rounding.

The present invention also has following further features:

1. In step 2, the area threshold S ₀ can be determined by the following method: separately calculate the area of the triangle formed by each convex point and two adjacent points in the original curve, since the median is not affected by a larger or smaller value, Therefore, the median of the area of the triangle is selected as the area threshold S ₀ .

2. In step 3, use the least squares method to curve fit the relationship between the distance threshold and the number of retained points, and select the optimal distance threshold D. Threshold-points optimal fitting curve, find the maximum curvature point where the curve drops rapidly, and the distance threshold at this point is the optimal distance threshold D, which represents the maximum balance point between compression ratio and quality.

3. In step 5, the sea area and thinning accuracy are balanced, and the evaluation factors include:

1) Area ratio: the ratio of the direction line and the natural shoreline to the area of the sea and land enclosed by the inland water and inland respectively;

2) Compression rate: the ratio of the amount of data compressed by vector data to the amount of data before compression;

3) Error area: the sum of the areas where the thinning curve deviates from the original curve. This indicator reflects the closeness of the thinning curve to the original curve.

4. In step 7, the specific steps of territorial sea base point encryption are as follows:

In step a, if the sum of the projection distances of the lines connecting adjacent territorial sea base points on the three coordinate axes under the three-dimensional coordinate system is greater than the encryption distance s, then go to step b, otherwise no encryption is performed;

Step b, according to the geodetic coordinates of the two territorial sea base points, use the geodetic theme inverse solution to obtain the geodetic length L and positive azimuth A of the two territorial sea base points;

Step c, if the geodetic length L of the two territorial sea base points is greater than the encryption distance s, it is necessary to perform encryption of [L/S] points;

Step d, according to the positive solution of the geodetic theme, taking the distance d and the positive azimuth A as known conditions, solve the geodetic coordinates and inverse azimuth of the first encrypted point; subtract 180° from the inverse azimuth of the first encrypted point to obtain the first The positive azimuth of an encrypted point; with the geodetic coordinates, positive azimuth and encrypted distance s of the first encrypted point as known conditions, the geodetic coordinates and its reverse azimuth of the second encrypted point are deduced, and so on, Until the geodetic coordinates of all encrypted points are obtained; where d=S%s+0.5*s, the operator % means to take the remainder.

5. In step b, use the Gaussian average argument inverse formula or the Bezier theme inverse algorithm to calculate the length of the geodetic line and the positive and negative azimuths between two points.

A method for extracting territorial sea baselines based on natural coastline data, mainly including the natural coastline thinning method based on the improved Douglas-Pucker algorithm and the territorial sea baseline encryption algorithm based on the geodetic calculation of the earth ellipsoid, in order to delineate the territorial sea baseline Certainly. In the process of thinning, the present invention extracts the natural coastline salient points that have a greater impact on the sea area as segment points, and then uses adjacent segment points as the first and last points of the Douglas-Pocke algorithm to fit them based on the least squares method. The curve selects the optimal distance threshold and thins out segment by segment, which can protect the national marine rights and interests while ensuring high accuracy and compression rate. In the encryption algorithm, the algorithm is based on the calculation of the geodetic line on the ellipsoidal surface of the earth, and the geodetic line is fitted between the adjacent territorial sea base points, and then the encryption calculation is performed between the adjacent base points by using the geodetic theme calculation principle. During the calculation process, the distance judgment conditions and the positions of encrypted points are improved, the calculation speed is improved, and the position distribution of the territorial sea base points is more reasonable. Moreover, the automatic extraction method of the territorial sea baseline of the present invention has higher computing efficiency.

Description of drawings

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 Flowchart of the improved piecewise Douglas-Peck algorithm.

Fig. 2 Example diagrams of natural coastline thinning under traditional and improved algorithms.

Figure 3 is an illustration of distance judgment.

Fig. 4 Flowchart of the encryption algorithm based on the geodetic solution of the earth ellipsoid.

Figure 5 Schematic diagram of the unencrypted territorial sea baseline.

Figure 6 Schematic diagram of the encrypted territorial sea baseline.

Detailed ways

Taking the South China Sea as an example, the present invention will be described in detail according to the accompanying drawings, so as to make the technical route and operation steps of the present invention clearer.

In this embodiment, the method for extracting the baseline of the territorial sea based on natural coastline data consists of an improved segmented Douglas-Puke algorithm (see Figure 1 for the flow chart) and an encryption algorithm based on the geodetic solution of the ellipsoid of the earth (see Figure 4 for the flow chart). Composition, the overall steps are as follows:

Step 1. Select salient points—for the natural coastline feature point set N, use the vector cross product formula to select salient points and store them in the point set M.

The characteristic of the Douglas-Peck algorithm is that as the distance threshold increases, the compression rate becomes larger, but the first and last points are always preserved. Therefore, the segmented Douglas-Pucker algorithm is used for curve compression, and the segmented points are used as the first and last points of the segmented Douglas-Pooker algorithm, which can always be retained, and the compression results retain the feature points with large curvature changes to the greatest extent. In the process of generating direction lines by thinning the natural coastline, in order to protect the national maritime rights and interests and maintain the integrity of the national sea area, under the framework of the United Nations Convention on the Law of the Sea, as many coastline salient points as possible should be retained, and the concave points should be discarded. Based on the above two considerations, the present invention proposes a segmented Douglas-Pocket algorithm using salient points as segment points, using the salient points as the first and last points of each thinning segment, and retaining the salient points to the greatest extent. This algorithm can maximize the accuracy and compression rate on the premise of ensuring the national sea area. Therefore, the algorithm first extracts the salient points of the natural shoreline.

Step 2. Select segment points—the first and last points in point set N are defaulted as segment points, which are directly stored in segment point set T; and the remaining points in point set M and the two adjacent points in point set N are calculated in turn The area value S of the triangle, if S≥S ₀ , then the point in the point set M is determined as a segment point and stored in the segment point set T, where S ₀ is the preset area threshold.

Using the area threshold to select segment points is one of the important steps of this algorithm. Since the number of natural shoreline salient points extracted by the vector cross product formula is often too large, if all the salient points are used as segment points, it will not reach The effect of compression, so some convex points are selected as segmentation points. Based on the needs of national marine interests, this paper selects some salient points that contribute greatly to the ocean area as segmentation points. The specific method is as follows: set the area threshold S0, and calculate the area S of the triangle formed by each convex point and two adjacent points on the original curve in turn. If S is greater than S0, keep this point until all points are judged.

Among them, the area threshold S ₀ can be determined by the following method: respectively calculate the triangle area formed by each convex point and two adjacent points in the original curve, since the median is not affected by a larger or smaller value, the triangle area is selected The median of is used as the area threshold S ₀ .

Step 3. Determine the optimal distance threshold D for each segment——for the natural coastline feature point set between adjacent segment points, select the optimal distance threshold D.

In this step, use the least square method to curve fit the relationship between the distance threshold and the number of retained points, and select the optimal distance threshold D. The number of points optimally fits the curve, and finds the maximum curvature point where the curve drops rapidly. The distance threshold at this point is the optimal distance threshold D, which represents the maximum balance point between compression ratio and quality.

Step 4. Segmented data thinning (Douglas-Puke algorithm is used for segmentation) - divide the natural coastline into several segmented coastlines by using segmented points, and take two adjacent segmented points as the first and last points of the segmented coastline, Using the optimal distance threshold D as the initial distance threshold, the Douglas-Pocke algorithm is used to extract data from the natural coastline in sections to obtain several candidate base points, and the connection lines of the candidate base points constitute the direction line.

From the first pair of adjacent segment points to the last segment point, for each segment, use the optimal distance threshold D obtained in step 3 to form a straight line by connecting the first and last points of the curve; calculate the distance from the middle points to this straight line Distance, find out the maximum distance and the maximum distance point; if it is less than the optimal distance threshold D, then use this straight line to replace the original curve, if it is greater than the optimal distance threshold D, divide the line segment into two segments at this point; for these two segments Repeat the above process, and the last remaining point is the result of data compression.

Step 5. Distance threshold adjustment—fine-tuning the distance threshold of the segmented coastline to balance the sea area and thinning accuracy, and obtain the corrected alternative base point and the corrected direction line.

In this step, the sea area and thinning precision are balanced, and the evaluation factors include:

1) Area ratio: the ratio of the direction line and the natural shoreline to the area of the sea and land enclosed by the inland water and inland respectively;

2) Compression ratio: the ratio of the amount of data compressed by vector data to the amount of data before compression;

3) Error area: the sum of the areas where the thinning curve deviates from the original curve. This indicator reflects the closeness of the thinning curve to the original curve.

After the above processing, the final direction line thinning result can be obtained. As shown in the example in Figure 2, under various thresholds, the area ratios obtained by using the algorithm of the present invention are respectively increased by 6.99%, 2.55%, 1.19%, and 1.30% compared with the traditional Douglas-Pocke algorithm. And under the four thresholds, the direction lines obtained by the algorithm in this paper are closer to the natural shoreline than the direction lines obtained by the traditional algorithm, and the error area is reduced by 0.03 km2, 0.44 km2, 0.11 km2, and 0.08 km2 respectively compared with the traditional algorithm. It can ensure the integrity of the sea area while ensuring high precision and compression rate, and its performance is obviously better than that of traditional algorithms, and better application results have been obtained.

Step 6. Acquisition of base points in the territorial sea—According to the United Nations Convention on the Law of the Sea, obtain the base points near the sea according to the revised alternative base points.

Step 7. Territorial sea base point encryption - for the geodetic length L between any two adjacent territorial sea base points, if it is greater than the preset encryption distance s, then increase [L/S ] encryption points, so that the geodetic length between adjacent points does not exceed the encryption distance s; where the operator [ ] represents rounding.

In this embodiment, the specific steps of territorial sea base point encryption are as follows:

In step a, if the sum of the projected distances of the lines connecting adjacent territorial sea base points on the three coordinate axes in the three-dimensional coordinate system is greater than the encryption distance s, then go to step b, otherwise no encryption will be performed.

The ideal distance judgment is to directly compare the geodetic distance between two points with the encryption distance, but the calculation of the geodetic line is too cumbersome, so the distance judgment conditions are optimized in this embodiment. As shown in Figure 3, suppose there are two adjacent points A(x1, y1, z1) and D(x2, y2, z2), and their geodetic lines on the ellipsoidal surface are arcs connecting the two points. The length of the arc is less than the length of the line segment AB+BC+CD, so when the sum of the projected distances of the line between two points on the three coordinate axes in the three-dimensional coordinate system (|x2-x1|+|y2-y1| +|z2-z1|) is less than the encryption distance s, which means that the length of the geodetic line at these two points must be less than the encryption distance s, and no encryption is required. Only when |x2-x1|+|y2-y1|+|z2-z1| is greater than the encryption distance s, it is necessary to use the positive solution of the earth to calculate the length of the earth line for further judgment. In the actual operation process, the geodetic coordinates are first transformed into space Cartesian coordinates. Since most of the territorial sea base points are relatively close, the improved distance judgment can greatly reduce the workload and improve the calculation efficiency.

Step b. According to the geodetic coordinates of the two territorial sea base points, the geodetic length L and the positive azimuth angle A of the two territorial sea base points are obtained by using the inverse solution of the geodetic theme. The inverse solution of the geodetic theme is a method of calculating the length of the geodetic line and the positive and negative azimuth angles between the two points given the geodetic coordinates. The commonly used specific algorithms include the Gaussian average argument inverse solution formula and the Bezier theme inverse solution.

Step c. If the geodetic length L of the two territorial sea base points is greater than the encryption distance s, [L/S] points need to be encrypted.

Step d, according to the positive solution of the geodetic theme, taking the distance d and the positive azimuth A as known conditions, solve the geodetic coordinates and inverse azimuth of the first encrypted point; subtract 180° from the inverse azimuth of the first encrypted point to obtain the first The positive azimuth of an encrypted point; with the geodetic coordinates, positive azimuth and encrypted distance s of the first encrypted point as known conditions, the geodetic coordinates and its reverse azimuth of the second encrypted point are deduced, and so on, Until the geodetic coordinates of all encrypted points are obtained; where d=S%s+0.5*s, the operator % means to take the remainder.

Figure 5 is a schematic diagram of the baseline of the unencrypted territorial sea, and Figure 6 is a schematic diagram of an encrypted distance of s=24 nautical miles.

When performing positive solution to calculate the encryption point, if the encryption is performed with the encryption distance s from the starting point, it is easy to cause the final encryption point to be too close to the end point, which is not conducive to the display effect and the shape of the baseline curve of the territorial sea. Therefore, all the encryption points are moved to the middle position of the geodetic line according to the distance requirements, so that the distance between the first encryption point and the starting point Q1 is approximately the same as the distance between the last encryption point and the end point Q2, that is, all the encryption points move toward the starting point Q1 The direction is moved by a distance d. The specific method is to use the distance d as a known element to perform an inverse solution when solving the first encryption point. For the subsequent encryption points, the encryption distance s is used as a known element to solve the problem. For the specific formula, see step d.

The encryption algorithm of the territorial sea baseline adopts the geodetic theme solution method, improves the distance judgment conditions and encrypted positions, and encrypts the territorial sea baseline by fitting the geodetic line. Encrypted points can be used as auxiliary points for territorial sea baselines to generate territorial sea baselines that conform to international norms, satisfy the fairness principle of sea area demarcation, and facilitate the development of sea area demarcation operations in the next step. The improved distance judgment conditions can simplify calculations and improve efficiency, especially for the situation where some territorial sea base points are dense. The improved encryption position expression makes the distribution of encryption points reasonable and obtains a better display effect.

In addition to the above-mentioned embodiments, the present invention can also have other implementations. All technical solutions formed by equivalent replacement or equivalent transformation fall within the scope of protection required by the present invention.

Claims (6)

1. extract the method for baselines of territorial sea based on natural water front data, it is characterized in that, comprise the steps:

Step 1, choose salient point---for nature coastline unique point point set N, utilize vector cross-products formula to select salient point, and stored in point set M;

Step 2, choose waypoint---the head and the tail point in point set N is defaulted as waypoint, directly stored in segmentation point set T; And to calculate in point set M in all the other each points and point set N successively at adjacent 2 and form leg-of-mutton area value S, if S>=S ₀, then in point set M, this point judges waypoint, stored in segmentation point set T, wherein, and S ₀for the area threshold preset;

Step 3, determine the optimal distance threshold value D of each segmentation---for the nature coastline unique point point set between adjacent sectional point, selected optimal distance threshold value D;

Step 4, segment data vacuate---utilize waypoint nature coastline to be divided into some segmentation shore lines, head and the tail point respectively using adjacent two waypoints as segmentation shore line, using described optimal distance threshold value D as initial distance threshold value, segmentation uses Douglas-Pu Ke algorithm to carry out data vacuate to nature coastline, obtain some alternative basic points, the line of alternative basic point forms direction line;

Step 5, distance threshold adjust---and the distance threshold in segmentation shore line is finely tuned, makes oceanic area and vacuate precision reach balance, obtain revised alternative basic point and revised direction line;

Step 6, territorial waters basic point obtain---according to the United Nations Convention on the Law of the Sea, obtain according to revised alternative basic point the basic point that borders on the sea;

Step 7, territorial waters basic point encrypt---for arbitrary neighborhood two territorial waters basic points between geodesic line length L, if be greater than default encryption distance s, then on the geodesic line of these two territorial waters basic points, increase [L/S] individual pass point, make the geodesic line length between consecutive point be no more than encryption distance s; Wherein operational symbol [] representative rounds.

2. the method extracting baselines of territorial sea based on natural water front data according to claim 1, is characterized in that: in step 2, area threshold S ₀determine by following methods: calculate adjacent 2 triangle areas formed in each salient point and virgin curve respectively, because median is not by the impact of value bigger than normal or less than normal, therefore select the median of triangle area as area threshold S ₀.

3. the method extracting baselines of territorial sea based on natural water front data according to claim 1; it is characterized in that: in step 3; utilize least square curve fit distance threshold with retain the relation of counting; selected optimal distance threshold value D; specific practice is; utilize the function formula of least square curve fit distance threshold and point; according to distance threshold-optimal fitting curve of counting; find the maximum curvature point that this curve declines fast; the distance threshold at this some place is optimal distance threshold value D, represents the maximum equilibrium point between compressibility and quality.

4. the method extracting baselines of territorial sea based on natural water front data according to claim 1, it is characterized in that: in step 5, make oceanic area and vacuate precision reach balance, evaluation factor comprises:

1), area ratio: the extra large land area ratio that direction line and natural water front enclose with interior water and inland respectively;

2), compressibility: the ratio of data volume before the data volume that Vector data compress methods falls and compression;

3), area of error: after vacuate, curve departs from the area sum of virgin curve, and after this index reflects vacuate, curve and virgin curve presses close to degree.

5. the method extracting baselines of territorial sea based on natural water front data according to claim 1, is characterized in that: in step 7, and the concrete steps of territorial waters basic point encryption are as follows:

If the projector distance sum between step a, adjacent territorial waters basic point in three coordinate axis of line under three-dimensional system of coordinate is greater than encryption distance s, then goes to step b, otherwise be not encrypted;

Step b, terrestrial coordinate according to two territorial waters basic points, utilize inverse solution of geodetic problem, obtain the geodesic line length L of two territorial waters basic points and square parallactic angle A;

If the geodesic line length L of the described two territorial waters basic points of step c is greater than encryption distance s, then need the encryption carrying out [L/S] individual point;

Steps d, according to direct solution of geodetic problem, with distance d, square parallactic angle A for known conditions, solve terrestrial coordinate and the reverse aximuth of first pass point; The reverse aximuth of first pass point deducts the square parallactic angle that 180 ° obtain first pass point; With the terrestrial coordinate of first pass point, square parallactic angle and encryption distance s for known conditions, inquire into terrestrial coordinate and its reverse aximuth of second pass point, by that analogy, until obtain the terrestrial coordinate of all pass points; Wherein d=S%s+0.5*s, operational symbol % represent remainder number.

6. the method extracting baselines of territorial sea based on natural water front data according to claim 5, is characterized in that: in step b, uses the anti-solution formula of the average argument of Gauss or the anti-resolving Algorithm of Bezier theme, calculates point-to-point transmission geodesic line length and positive reverse aximuth.