CN110569445A - position-based neighbor detection method in social network - Google Patents

Abstract

the invention discloses a neighbor detection method in a social network based on positions, which is an important problem in the social network service based on the positions. Neighbor detection allows the user to select a particular geometric range on the map and then ask if his friend is within that range. In order to efficiently realize the neighbor detection in the social network, the geometric range selected by a user is abstracted into a convex polygon, the position of a friend of the user is abstracted into a point, then four characteristic vertexes of the convex polygon are extracted, one division of the convex polygon can be realized according to the four characteristic vertexes, then the given point is judged to fall into which partition, the judgment condition corresponding to the partition is called to judge the position relation between the given point and the convex polygon, and the result is finally obtained. The invention can obtain the position relation between the point and the convex polygon only by judging the point and the side once, thereby efficiently solving the problem of neighbor detection in the social network.

Description

position-based neighbor detection method in social network

Technical Field

the invention belongs to the technical field of social networks, relates to a neighbor detection method in a social network, and particularly relates to a method for performing neighbor detection by using a position relation between a point and a convex polygon in a position-based social network service.

Background

With the popularization of location-aware mobile terminals and the popularization of social applications, location-based social networking services (lbs ns) bring great convenience to the lives of people. Among them, the neighbor detection service is a typical application of the LBS. Neighbor detection allows the user to select a particular geometric range on the map and then ask if his friend is within that range. Generally, a geometric range selected by a user is abstracted into a convex polygon, the position of a friend of the user is abstracted into a point, and the problem of neighbor detection is solved by judging the position relation between the point and the convex polygon.

The current method for judging the point and the convex polygon comprises the following steps: the orientation of the points is calculated (document 1), the ray method (document 2), the included angle method (document 3), the area method (document 4), and the like. In the method for calculating the orientation of the points, the orientation of the points and each side of the convex polygon needs to be judged; in the angle clamping method, the included angle between the point and each side of the convex polygon needs to be calculated; in the area method, the problem of the positions of points and convex polygons needs to be converted into a triangular area problem, and then the triangular area problem is solved, so that the methods generally have the problem of low calculation efficiency. In the ray method, a ray is led out through a given point, the number of intersection points of the ray and a convex polygon is calculated, if the number of the intersection points is an odd number, a coordinate point is in the convex polygon, and otherwise, the coordinate point is outside the convex polygon. However, when the given point is located on the convex polygon side, the method has a possibility of erroneous judgment. Therefore, how to efficiently implement the proximity detection in the social network is still a problem worthy of research.

[1]F.Feito,J.C.Torres,and A.Orientation,simplicity,and inclusion test for planar polygons[J].Comput.Graph.,1995,19(4):595–600.

[2]GALETZKA M,GLAUNER P O.A simple and correct even-odd algorithm for the point-in-polygon problem for complex polygons[OL].In:Proceedings of the12th International Joint Conference on Computer Vision,Imaging andComputer Graphics Theory and Applications(VISIGRAPP 2017).Porto,Portugal,2017:175-178.

[3]HORMANN K,AGATHOS A.The point in polygon problem for arbitrary polygons[J].Computational Geometry,2001,20(3):131-144.

[4] Chenzhuihua, Lishundong, Huangqiong, Donglihong, Chenpidang, two new solutions for the problem of secret position judgment [ J ] reported by computer, 2018,41(2):336-348.

Disclosure of Invention

In order to solve the above problems, the present invention provides a method for performing neighbor detection using a position relationship between a point and a convex polygon in a location-based social networking service.

The technical scheme adopted by the invention is as follows: a neighbor detection method in a social network based on positions is characterized in that a geometric range specified by a user is a convex polygon L with n vertexes, and the geometric range is sequentially numbered anticlockwise from the vertex with the largest ordinate, and is assumed to be { P₁,P₂,…,P_nAre respectively (x) in coordinates_i,y_i) I-1, 2, …, n, and represents the location of the user's friend as a point P (x)_p,y_p) Judging the position relation between the point P and the convex polygon L, namely judging whether the point P is positioned outside or inside the convex polygon L; the point P is positioned inside the convex polygon L and comprises the condition that the point P is positioned on the side of the convex polygon L; if the point P is positioned outside the convex polygon L, the situation that the friends of the user are not in the geometric range specified by the user is shown; if the point P is positioned inside the convex polygon L, the situation that the friend of the user is positioned in the geometric range specified by the user is shown;

characterized in that the method comprises the following steps:

step 1: finding four characteristic vertexes of the convex polygon L: a top vertex, a left vertex, a bottom vertex and a right vertex; the uppermost vertex is marked as P₁Let the leftmost vertex be denoted as P_lThe lowest vertex is denoted as P_dAnd the rightmost vertex is marked as P_rIf l is more than or equal to 1 and less than or equal to d and less than or equal to r and less than or equal to n;

Step 2: judging the position relation between the given point P and the convex polygon L;

And step 3: if the point P is inside the convex polygon L, returning that the friend of the user is positioned in the geometric range specified by the user; if the point P is outside the convex polygon L, the friend returning to the user is not within the user-specified geometric range.

preferably, the specific implementation of step 2 comprises the following sub-steps:

step 2.1: if y is_p<y_dOr y_p>y₁Or x_p<x_lOr x_p>x_rThen, given point P (x)_p,y_p) The flow is finished when the convex polygon L is positioned outside the convex polygon L;

Otherwise, entering step 2.2;

step 2.2: if x_p≤x₁and y is_p≥y_lAt this time, the given point P (x)_p,y_p) At the uppermost vertex P₁Left and leftmost vertex P_lAt this time, the judgment process I is executed, and the process is ended;

Otherwise, entering step 2.3;

The specific implementation of the judgment process I comprises the following sub-steps:

Step 2.2.1: at the vertex { P₁,P₂,…,P_lFind two adjacent vertexes P_iAnd P_i+1So that x is_i≤x≤x_i+1Wherein i is more than or equal to 1 and less than or equal to l-1;

Step 2.2.2: computing over-vertex P_iand P_i+1Straight line of (2), with the symbol f₁(x) Represents the straight line;

Step 2.2.3: if y is_p≤f₁(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Located outside the convex polygon L;

Step 2.3: if x_p≤x_dAnd y is_p<y_lAt this time, the given point P (x)_p,y_p) At the lowest vertex P_dLeft and leftmost vertex P_lAt this time, the judgment process II is executed, and the process is ended;

Otherwise, entering step 2.4;

The specific implementation of the judgment process II comprises the following substeps:

Step 2.3.1: at the vertex { P_l,P_l+1,P_l+2,…,P_dfind two adjacent vertexes P_iAnd P_i+1so that x is_i+1≤x≤x_iWherein l-1 is more than or equal to i is more than or equal to d;

Step 2.3.2: computing over-vertex P_iAnd P_i+1straight line of (2), with the symbol f₂(x) Represents the straight line;

Step 2.3.3: if y is_p≥f₂(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Located outside the convex polygon L;

Step 2.4: if x_p>x_dAnd y is_p<y_rAt this time, the given point P (x)_p,y_p) At the lowest vertex P_dright side and rightmost vertex P of_rAt this time, the judgment process III is executed, and the process is ended;

Otherwise, entering step 2.5;

the specific implementation of the judgment process III includes the following substeps:

Step 2.4.1: at the vertex { P_d,P_d+1,P_d+2,…,P_rFind two adjacent vertexes P_iAnd P_i+1So that x is_i≤x≤x_i+1Wherein d is not less than i and not more than r-1;

Step 2.4.2: computing over-vertex P_iAnd P_i+1straight line of (2), with the symbol f₃(x) Represents the straight line;

step 2.4.3: if y is_p≥f₃(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Located outside the convex polygon L;

step 2.5: if x_p>x₁And y is_p≥y_rAt this time, the given point P (x)_p,y_p) At the uppermost vertex P₁Right side and rightmost vertex P of_rAt this time, the judgment process IV is executed, and the process is ended;

The specific implementation of the judgment process IV includes the following substeps:

Step 2.5.1: if x₁≤x≤x_nselecting the vertex P_nAnd P₁Otherwise at vertex { P_r,P_r+1,P_r+2,…,P_nFind two adjacent vertexes P_iAnd P_i+1So that x is_i+1≤x≤x_iWherein r-1 is not less than i and not more than n;

Step 2.5.2: if the selected vertex is P_nand P₁Then the vertex P is calculated_nAnd P₁Otherwise, the vertex P is calculated_iand P_i+1Straight line of (2), with the symbol f₄(x) Representing the calculated straight line;

Step 2.5.3: if y is_p≤f₄(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Outside the convex polygon L.

Aiming at the problems of low calculation cost and low efficiency of the existing method, the invention discloses a neighbor detection method in a social network based on position; abstracting a geometric range selected by a user into a convex polygon, abstracting the position of friends of the user into a point, extracting four characteristic vertexes of the convex polygon, dividing the convex polygon according to the four characteristic vertexes, and giving a position judgment process of an inner point of each partition and the convex polygon; and finally, judging which partition the point falls into according to the coordinates of the given point, and then executing a corresponding position judgment process to finally obtain a solution of the problem. In the method provided by the invention, the given point does not need to carry out position judgment on all sides of the convex polygon and problem conversion, so that the calculation expense is greatly reduced.

Drawings

FIG. 1: a convex polygon is given according to the embodiment of the invention;

FIG. 2: the given convex polygon of the embodiment of the invention is divided into schematic diagrams;

FIG. 3: a method flow diagram of an embodiment of the invention;

FIG. 4: the schematic diagram of the position relation between the first point and the given convex polygon in the embodiment of the invention;

FIG. 5: the schematic diagram of the position relationship between the second point and the given convex polygon in the embodiment of the invention;

FIG. 6: a schematic diagram of a positional relationship between a third point and a given convex polygon in the embodiment of the present invention;

FIG. 7: a schematic diagram of a position relationship between a fourth point and a given convex polygon in the embodiment of the present invention;

FIG. 8: a schematic diagram of a position relationship between a fifth point and a given convex polygon in the embodiment of the invention;

FIG. 9: a schematic diagram of a position relationship between a sixth point and a given convex polygon in the embodiment of the present invention;

FIG. 10: a schematic diagram of a position relationship between a seventh point and a given convex polygon in the embodiment of the present invention;

FIG. 11: a schematic diagram of a positional relationship between an eighth point and a given convex polygon in the embodiment of the present invention;

FIG. 12: the ninth point of the embodiment of the invention is a schematic diagram of the position relation of a given convex polygon.

Detailed description of the invention

In order to facilitate the understanding and implementation of the present invention for those of ordinary skill in the art, the present invention is further described in detail with reference to the accompanying drawings and examples, it is to be understood that the embodiments described herein are merely illustrative and explanatory of the present invention and are not restrictive thereof.

Referring to FIG. 1, assume that the geometric range specified by the user is a convex polygon L having n vertices, which are numbered counterclockwise in order from the vertex with the largest ordinate, and are assumed to be { P₁,P₂,…,P_nAre respectively (x) in coordinates_i,y_i)，i＝1,2, …, n. Wherein four characteristic vertexes are P₁(uppermost vertex), P_l(leftmost vertex), P_d(lowest vertex), P_r(rightmost vertex).

Referring to fig. 2, the position of the friend of the user is represented as a point P, and a convex polygon is divided according to four feature vertices, so as to obtain 5 partitions: the first partition corresponds to the blank area in fig. 2, and if the point P falls into this area, it is indicated that the point P is outside the convex polygon (see fig. 4); the second partition corresponds to the shaded area labeled I in fig. 2, and if the point P falls into this area, it needs to further judge its positional relationship with the convex polygon (see fig. 5 and 6); the third partition corresponds to the shaded area labeled II in fig. 2, and if the point P falls into this area, it needs to further judge its positional relationship with the convex polygon (see fig. 7 and 8); the fourth partition corresponds to the shaded area labeled III in fig. 2, and if the point P falls into this area, it needs to further judge its positional relationship with the convex polygon (see fig. 9 and 10); the fifth partition corresponds to the shaded area labeled IV in fig. 2, and if the point P falls into this area, it needs to be further judged as to its positional relationship with the convex polygon (see fig. 11 and 12).

Referring to fig. 3, the method for detecting a neighbor in a social network based on a location provided by the present invention includes the following steps:

step 1: finding four characteristic vertexes of the convex polygon L: uppermost vertex, leftmost vertex, lowermost vertex, and rightmost vertex. According to the above numbering rule, the uppermost vertex is P₁Let P be the leftmost vertex_lThe lowest vertex is P_dThe rightmost vertex is P_rAnd d is more than or equal to 1 and less than or equal to r and less than or equal to n. One division of the convex polygon is actually realized on the basis of four feature vertices, see fig. 2, where a given convex polygon is divided into 5 partitions.

step 2: the positional relationship between the predetermined point P and the convex polygon L is determined.

Referring to steps 2.1 to 2.5 in fig. 3 and fig. 4 to 12, the specific implementation of step 2 includes the following sub-steps:

Step 2.1: if y is_p<y_dOr y_p>y₁Or x_p<x_lOr x_p>x_ri.e. point P (x)_p,y_p) Falls into the blank region (corresponding to the case shown in FIG. 4), a point P (x) is given_p,y_p) The convex polygon L is positioned outside the convex polygon L, otherwise, the step 2.2 is carried out;

Step 2.2: if x_p≤x₁and y is_p≥y_lI.e. point P (x)_p,y_p) Falls into region I, at which point the following steps 2.2.1 to 2.2.3 are performed, otherwise step 2.3 is entered.

step 2.2.1: at the vertex { P₁,P₂,…,P_lFind two adjacent vertexes P_iAnd P_i+1So that x is_i≤x≤x_i+1wherein i is more than or equal to 1 and less than or equal to l-1;

Step 2.2.2: computing over-vertex P_iAnd P_i+1Straight line of (2), with the symbol f₁(x) Represents the straight line;

Step 2.2.3: if y is_p≤f₁(x_p) (corresponding to the case shown in FIG. 5), the point P (x) is given_p,y_p) Is located inside the convex polygon L, otherwise (corresponding to the situation shown in FIG. 6) a given point P (x)_p,y_p) Outside the convex polygon L.

Step 2.3: if x_p≤x_dAnd y is_p<y_lI.e. point P (x)_p,y_p) Falls into region II, at which point the following steps 2.3.1 to 2.3.3 are performed, otherwise step 2.4 is entered.

step 2.3.1: at the vertex { P_l,P_l+1,P_l+2,…,P_dFind two adjacent vertexes P_iAnd P_i+1so that x is_i+1≤x≤x_iWherein l-1 is more than or equal to i is more than or equal to d;

Step 2.3.2: computing over-vertex P_iAnd P_i+1Straight line of (2), with the symbol f₂(x) Represents the straight line;

Step 2.3.3: if y is_p≥f₂(x_p) (corresponding to the case shown in FIG. 7), the point P (x) is given_p,y_p) Is located inside the convex polygon L, otherwise (corresponding to the situation shown in FIG. 8) a given point P (x)_p,y_p) Outside the convex polygon L.

step 2.4: if x_p>x_dAnd y is_p<y_rI.e. point P (x)_p,y_p) Falls into region III, at which point the following steps 2.4.1 to 2.4.3 are performed, otherwise step 2.5 is entered.

Step 2.4.1: at the vertex { P_d,P_d+1,P_d+2,…,P_rFind two adjacent vertexes P_iAnd P_i+1So that x is_i≤x≤x_i+1Wherein d is not less than i and not more than r-1;

Step 2.4.2: computing over-vertex P_iAnd P_i+1Straight line of (2), with the symbol f₃(x) Represents the straight line;

Step 2.4.3: if y is_p≥f₃(x_p) (corresponding to the case shown in FIG. 9), the point P (x) is given_p,y_p) Is located inside the convex polygon L, otherwise (corresponding to the situation shown in FIG. 10) a given point P (x)_p,y_p) Outside the convex polygon L.

step 2.5: at this time x_p>x₁And y is_p≥y_ri.e. point P (x)_p,y_p) Falling within region IV, the following steps 2.5.1 to 2.5.3 are performed.

Step 2.5.1: if x₁≤x≤x_nSelecting the vertex P_nAnd P₁otherwise at vertex { P_r,P_r+1,P_r+2,…,P_nFind two adjacent vertexes P_iAnd P_i+1So that x is_i+1≤x≤x_iWherein r-1 is not less than i and not more than n;

Step 2.5.2: if the selected vertex is P_nAnd P₁Then the vertex P is calculated_nAnd P₁Otherwise, the vertex P is calculated_iAnd P_i+1Straight line of (2), with the symbol f₄(x) Representing the calculated straight line;

Step 2.5.3: if y is_p≤f₄(x_p) (corresponding to FIG. 1)1), point P (x) is given_p,y_p) Is located inside the convex polygon L, otherwise (corresponding to the situation shown in FIG. 12) a given point P (x)_p,y_p) Outside the convex polygon L.

And step 3: if the point P is inside the convex polygon L, returning that the friend of the user is positioned in the geometric range specified by the user; if the point P is outside the convex polygon L, the friend returning to the user is not within the user-specified geometric range.

Aiming at the problem of neighbor detection in a social network, firstly abstracting a geometric range selected by a user into a convex polygon, abstracting the position of friends of the user into a point, then extracting four characteristic vertexes of the convex polygon, dividing the convex polygon according to the four characteristic vertexes, and giving a position judgment process of an inner point of each partition and the convex polygon; and finally, judging which partition the point falls into according to the coordinates of the given point, and then executing a corresponding position judgment process to finally obtain a solution of the problem. The invention can obtain the position relation between the point and the convex polygon only by judging the point and the side once, thereby efficiently solving the problem of neighbor detection in the social network.

It should be understood that parts of the specification not set forth in detail are well within the prior art.

It should be understood that the above description of the preferred embodiments is given for clarity and not for any purpose of limitation, and that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (2)

1. A neighbor detection method in a social network based on positions is characterized in that a geometric range specified by a user is a convex polygon L with n vertexes, and the geometric range is sequentially numbered anticlockwise from the vertex with the largest ordinate, and is assumed to be { P₁,P₂,…,P_nAre respectively (x) in coordinates_i,y_i)，i1,2, …, n, and represents the location of the user's friend as a point P (x)_p,y_p) Judging the position relation between the point P and the convex polygon L, namely judging whether the point P is positioned outside or inside the convex polygon L; the point P is positioned inside the convex polygon L and comprises the condition that the point P is positioned on the side of the convex polygon L; if the point P is positioned outside the convex polygon L, the situation that the friends of the user are not in the geometric range specified by the user is shown; if the point P is positioned inside the convex polygon L, the situation that the friend of the user is positioned in the geometric range specified by the user is shown;

Characterized in that the method comprises the following steps:

Step 1: finding four characteristic vertexes of the convex polygon L: a top vertex, a left vertex, a bottom vertex and a right vertex; the uppermost vertex is marked as P₁Let the leftmost vertex be denoted as P_lthe lowest vertex is denoted as P_dAnd the rightmost vertex is marked as P_rIf l is more than or equal to 1 and less than or equal to d and less than or equal to r and less than or equal to n;

step 2: judging the position relation between the given point P and the convex polygon L;

And step 3: if the point P is inside the convex polygon L, returning that the friend of the user is positioned in the geometric range specified by the user; if the point P is outside the convex polygon L, the friend returning to the user is not within the user-specified geometric range.

2. The method for detecting the nearest neighbor in the social network based on the position as claimed in claim 1, wherein the step 2 comprises the following steps:

step 2.1: if y is_p<y_dOr y_p>y₁Or x_p<x_lOr x_p>x_rThen, given point P (x)_p,y_p) The flow is finished when the convex polygon L is positioned outside the convex polygon L;

Otherwise, entering step 2.2;

step 2.2: if x_p≤x₁And y is_p≥y_lat this time, the given point P (x)_p,y_p) At the uppermost vertex P₁Left and leftmost vertex P_lAt this time, the judgment is performedprocess I, the process is finished;

Otherwise, entering step 2.3;

The specific implementation of the judgment process I comprises the following sub-steps:

Step 2.2.1: at the vertex { P₁,P₂,…,P_lFind two adjacent vertexes P_iand P_i+1So that x is_i≤x≤x_i+1Wherein i is more than or equal to 1 and less than or equal to l-1;

Step 2.2.2: computing over-vertex P_iAnd P_i+1Straight line of (2), with the symbol f₁(x) Represents the straight line;

step 2.2.3: if y is_p≤f₁(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Located outside the convex polygon L;

Step 2.3: if x_p≤x_dAnd y is_p<y_lat this time, the given point P (x)_p,y_p) At the lowest vertex P_dLeft and leftmost vertex P_lAt this time, the judgment process II is executed, and the process is ended;

otherwise, entering step 2.4;

The specific implementation of the judgment process II comprises the following substeps:

step 2.3.1: at the vertex { P_l,P_l+1,P_l+2,…,P_dfind two adjacent vertexes P_iAnd P_i+1so that x is_i+1≤x≤x_iwherein l-1 is more than or equal to i is more than or equal to d;

Step 2.3.2: computing over-vertex P_iand P_i+1Straight line of (2), with the symbol f₂(x) Represents the straight line;

Step 2.3.3: if y is_p≥f₂(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Located outside the convex polygon L;

Step 2.4: if x_p>x_dAnd y is_p<y_rAt this time, the given point P (x)_p,y_p) At the lowest vertex P_dRight side and rightmost vertex P of_rAt this time, the judgment process III is executed, and the process is ended;

Otherwise, entering step 2.5;

The specific implementation of the judgment process III includes the following substeps:

step 2.4.1: at the vertex { P_d,P_d+1,P_d+2,…,P_rFind two adjacent vertexes P_iAnd P_i+1So that x is_i≤x≤x_i+1Wherein d is not less than i and not more than r-1;

Step 2.4.2: computing over-vertex P_iand P_i+1Straight line of (2), with the symbol f₃(x) Represents the straight line;

step 2.4.3: if y is_p≥f₃(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Located outside the convex polygon L;

Step 2.5: if x_p>x₁and y is_p≥y_rat this time, the given point P (x)_p,y_p) At the uppermost vertex P₁right side and rightmost vertex P of_rAt this time, the judgment process IV is executed, and the process is ended;

The specific implementation of the judgment process IV includes the following substeps:

step 2.5.1: if x₁≤x≤x_nSelecting the vertex P_nAnd P₁Otherwise at vertex { P_r,P_r+1,P_r+2,…,P_nfind two adjacent vertexes P_iAnd P_i+1So that x is_i+1≤x≤x_iwherein r-1 is not less than i and not more than n;

Step 2.5.2: if the selected vertex is P_nAnd P₁Then the vertex P is calculated_nand P₁Otherwise, the vertex P is calculated_iAnd P_i+1Straight line of (2), with the symbol f₄(x) Representing the calculated straight line;

Step 2.5.3: if y is_p≤f₄(x_p) Then, given point P (x)_p,y_p) Located inside the convex polygon L, otherwise given a point P (x)_p,y_p) Outside the convex polygon L.