CN111985065A - Road automatic selection technology based on gravitational field theory - Google Patents
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Abstract
The complex network model is widely applied to automatic road selection, but few methods consider the influence of multi-level neighbor nodes in the road network dual graph, and the importance evaluation of the road is lack of accuracy and reliability. Therefore, a road automatic selection technology based on the gravitational field theory is provided, and the basic idea is as follows: firstly, generating a road network dual graph by means of strokes; then, calculating the centrality measurement value of the nodes by adopting a centrality method, regarding the centrality measurement value as mass, regarding the shortest distance between the nodes as distance, and evaluating the importance of stroke by utilizing a Newton gravity formula; and finally, automatically selecting the roads by selecting the strokes with the importance degree ranked in front. The road network of the Lanzhou city gateway area is tested, and the result shows that the road network selected by the invention better keeps the integral structure, coverage, density distribution, topological characteristics and connectivity of the original road network.
Description
Technical Field
The invention belongs to the technical field of comprehensive drawing, and relates to research on automatic road selection.
Background
A road network is one of typical representatives of a mesh element among map elements, and is an important object of map synthesis. Road selection is a prerequisite for other comprehensive operations, and usually, the importance of roads is measured according to measurement, statistics, topology and thematic information implied by a road network or a single road, and roads with the importance ranking before are selected. Road selection not only simply reduces the detail of the road network, but also maintains the overall structure and local key structure, density distribution, coverage and the like of the road.
The current road automatic selection method mainly adopts graph theory and a complex network model. Compared with a method based on a complex network model, road selection based on graph theory cannot well describe the complexity and the overall shape of a road network structure, and the complex network is a model recognized by a simulated complex system. Therefore, the method for establishing the complex network model of the road network by using the dual topology method is widely applied. The method has the advantages that indexes such as semantics, geometry, node degree, medium neutrality, approach centrality and the like of integrated roads such as Zhangdong and the like are selected by giving weights to various indexes according to drawing experience, and semantic information of the roads is often incomplete and difficult to acquire, so that the method has certain limitation in application; li mu catalpa and the like calculate the accumulated weight number by constructing a hierarchical clustering structure of a road network, so that the importance of the road in the overall structure is measured, but the model has higher calculation complexity; liu Jiang and the like consider the importance of the nodes and the influence of nearby nodes, the road importance is evaluated by combining the node degrees of the dual graph and the mesocentrality, and the selected result can better keep the structural characteristics, topological characteristics and connectivity of the road, but excessive parameters in the method are determined by experience values, and inconsistent selected results can be caused by different parameter settings; and the Caowenw et al considers the length of the stroke, the degree of nodes of the dual graph and the clustering coefficient, determines the weights of different indexes by using a coefficient of variation method and selects the road. However, the road evaluation index of the model can only reflect the local attribute of the road; the method well maintains the hierarchy of the road network and reduces the influence of 'edge effect', but the connectivity of road network layers is damaged after the method is selected.
Disclosure of Invention
At present, the influence of multi-level neighbor nodes is mostly not considered in a method for selecting a road by using a complex network model, so that the importance evaluation of the road lacks accuracy and reliability, and the importance of the nodes in the complex network is not only dependent on the importance of the nearest nodes but also influenced by the multi-level neighbor nodes. Therefore, the road network is mapped into the dual graph by means of strokes, the centrality measurement value of the dual graph nodes and the shortest distance between the nodes are respectively regarded as the quality and the distance in the gravitational field equation, the importance evaluation model of the dual graph nodes is established, and the automatic road selection technology considering the influence of the multi-level neighbor nodes is further provided.
Automatic road selection technology
1.1 Stroke-unit-based dual topology expression of road network
In the research of road automatic selection, there are mainly two road expression modes: one method is to establish generalized road network topology by taking road units as edges and intersections as nodes; and the other method is to map the road network into a dual graph by using a dual topology method and taking road units as nodes and road intersections as edges.
Can use simple unauthorized drawingTo define a dual graph in which,representing the number of nodes in the dual graph, Indicating the number of connected edges in the dual graph. Two ways of expressing the road network are shown in figure 1. Compared with the generalized road network topology, the dual topology method can clearly express the connection relation among roads, the importance degree of the roads in the network and the local and global efficiency of the road network, so that the dual graph is beneficial to further analyzing the structural characteristics and the overall form of the roads. stroke refers to a combination of road segments with good continuity in direction, which is superior to the road segments in terms of keeping the longitudinal gradation and geometrical characteristics of the road.
Therefore, the method carries out dual topological expression on the road network by taking strokes as units.
1.2 evaluation of Stroke importance
1.2.1 centrality measure analysis
The centrality index is based on the importance of the nodes in the network structure evaluation network, and can be mathematically summarized into centrality, intermediary centrality and approximate centrality. The three indexes reflect local and global topological properties of nodes in the network. In addition, in order to take the geometric characteristics of roads into consideration, the stroke length is also introduced into the centrality measure analysis.
(1) Center of gravity
Centrality refers to the number of edges connected to a node. The method can determine the local influence of the node most effectively, and has the defect that the influence of the first-level neighbor node is only utilized, so that the importance of the node in the network is often required to be evaluated by combining other indexes. Node point Value of (A)Can be expressed by equation (1):
wherein the content of the first and second substances,representing the number of nodes in the network. If nodeAndthe two parts are directly connected with each other,is 1; otherwiseIs 0.
(2) Center of medium
The intermediary centrality reflects the importance of the node when performing path selection, in other words, represents the significance of the "intermediary" influence of the node in the network, and the theoretical formula is represented as:
wherein the content of the first and second substances,is the total number of nodes of the network,andon behalf of any two nodes in the network,representative nodeAndthe number of shortest paths between the two,representative nodeAndall shortest paths ofThe number of the cells.The larger the value, the nodeThe more pronounced the "mediator" function, the more important it is.
(3) Near centrality
The proximity centrality reflects the proximity of a node to all other nodes in the network, and means the reciprocal of the average shortest distance between any node and all other nodes in the network. The greater the proximity centrality value of a node is, the closer it is to other nodes, the more the node is located in the center of the network, the higher its importance is, and it is recorded as:
wherein the content of the first and second substances,indicating the number of nodes in the network,which represents any one of the nodes in the network,representing nodesAndthe shortest distance therebetween.
(4) Length of stroke
Length of stroke: () The index describes the range of influence of a stroke as the sum of the lengths of the road segments that make up the stroke. The longer the length of stroke, the greater the range of influence and the higher the importance.
1.2.2 index integration
Because the dimensions and the magnitude of the indexes are different,in order to not highlight the influence of a certain index with a high value, each index needs to be subjected to dispersion standardization so that the value range is [0,1 ]]In the meantime. In addition, the CRITIC weighting method is selected to give weight to each index. The CRITIC weighting method uses standard deviation to measure the contrast intensity in the indexes and uses the correlation coefficient to measure the conflict intensity between the indexes, so as to make the information amount reach the maximum. First, theInformation amount of individual indexCan be expressed by equation (4):
wherein the content of the first and second substances,indicating indexThe standard deviation of (a) is determined,the number of the indexes is represented,indicating indexAndthe correlation coefficient of (2). From this, an index can be obtainedThe higher the information amount of (2), the higher the importance of the index to other indexes, so that the indexWeight of (2)Can be expressed as:
Wherein、、、Respectively are the weights of four indexes,、、、is a node after dispersion standardizationCentrality, mesocentrality, recenterness, and stroke length values.
1.3 Stroke importance evaluation method combining gravitational field theory
The importance of nodes in a network is typically affected by multiple levels of neighboring nodes, with the effect between nodes becoming weaker as the shortest distance between them increases. On the basis of the obtained node centrality measurement value, the following click importance evaluation method is proposed:
wherein the content of the first and second substances,representing nodesAndthe shortest distance between the two elements,andis a nodeAnda centrality measure of;is a nodeA set of neighboring nodes of, a node to node in the setDoes not exceed a given range. Because the time complexity of the shortest path algorithm such as Dijkstra or bellman-ford is very high, the following algorithm is adopted to obtain a multi-stage neighbor node set:
node pointThe distance between the node and the neighbor node is 1, and the nodeNeighbor node and node of neighbor nodeIs 2, and so on. In this way, the nodes are acquired step by stepAnd each node therein is endowed with the nodeThe shortest distance value of. Node pointA schematic diagram of a multi-level neighbor node of (2) is shown.
The method integrates the length of the strokes and various centrality indexes and combines a Newton gravity formula to calculate the importance of the nodes of the dual graph, thereby considering the geometrical and topological properties of the strokes, the shortest distance between the nodes and the influence of multi-level neighbor nodes, and being capable of evaluating the importance of the strokes more accurately and comprehensively.
1.4 automatic road selection process
Mapping the road network into a dual graph by taking strokes as a unit; obtaining the importance sequence of strokes by using the method provided by 1.3, selecting the roads with the front rank according to the selection proportion to form a road network; and finally, maintaining the global connectivity through a connectivity maintaining algorithm. The specific process of road selection is as follows:
(1) and generating a stroke network by using the original road network.
(2) Mapping the stroke network into a dual graph defined as,The number of nodes in the network is represented,representing the number of edges in the network.
(3) The centrality measure values for all nodes in the dual graph are calculated from the 1.2.2 integrated polynomial indices.
(4) For any node in the networkObtaining a nodeAnd itThe level neighbor nodes regard the centrality measurement values thereof as quality; simultaneous acquisition nodeAnd itThe shortest path of each node in the level neighbor node set is regarded as a distance; solving for nodes according to 1.3The importance of (c). And repeating the execution until the importance of all the nodes is solved.
(6) Selecting from big to small according to the importance of the nodes of the dual graphA node and its connecting edgeForming a network。
(7) According to the method for maintaining connectivity of 1.5, maintaining All-around communication.
1.5 connectivity maintenance
The strokes selected according to the importance ranking may form several parts that are not connected to each other, and thus the global connectivity of the network cannot be maintained. Some lower-ranked roads connecting these disconnected parts should also be reserved. The following conditions should be followed in connection with connectivity maintenance:adding as few new nodes as possible.And preferentially adding the nodes with higher importance. Thus, first a road network dual graph is definedMiddle edgeThen, the edge weight and the maximum spanning tree are obtained for maintaining the connectivity.
1.5.1 redefinition of dual graph edge weights
The importance of each edge in an unweighted complex network is different and is influenced by the importance of the two nodes that make up it. So if the importance of two nodes is higher in the dual graph, the importance of the edge they compose is also higher. Therefore, the edge weights are defined as follows:
wherein the content of the first and second substances,representing nodesAndthe weight of the constituent edges is such that,andrespectively represent the nodes obtained in 3.3Andthe importance of (c). Thus, the dual graph is constructed as a weighted graph.
1.5.2 connectivity maintenance Algorithm
Taking fig. 3 as an example, fig. 3 (a) shows a dual graph of an original road network, black nodes show selected strokes with higher importance, white nodes show other strokes in the original road network, and it can be seen from the graph that the network formed by the selected strokes does not maintain connectivity. The method orders the edges of the network from big to small according to the weight, and then calculates the edge weight and the maximum spanning tree. The specific steps of the connectivity maintaining method are as follows:
(2) Building spanning treesAt the beginning of,And = 0. Will be provided withEach node in (a) is considered as an independent tree.
(3) According to the weight value from large to smallIn the selection edge is added toThe two vertices of the selected edge should belong to different trees and the two trees are merged into one tree.
(4) Repeating the step (3) until all nodes are in the same tree, and obtaining the result as shown in fig. 3 (b).
(5) Judgment ofWhether the leaf node in (1) belongs to the selected node setAnd if not, deleting the data. This step is performed iteratively untilThere are no leaf nodes in (fig. 3 (c)).
(6)The remaining nodes in the list are strokes selected after the connectivity is maintained (fig. 3 (d)).
2 experiments and analysis
The experimental data is a generalized road network topological graph of a Lanzhou city customs area, as shown in FIG. 4. The reason for selecting the data is that roads in the area are closely connected, the road network is complex, and relatively obvious relative density distribution difference exists, so that the selection effect can be effectively reflected. The deflection angle threshold value was set to 45。And generating the strokes, and then mapping the strokes network into a dual graph. The generated dual graph contains 420 nodes, 1941 edges, a network diameter of 11, and an average shortest path of 4.601. Weights of four indexes 、、、The calculation results of (a) were 0.196, 0.150, 0.447, 0.207.
(1) According to the present technique, the importance of each node is from 0 toLevel neighbor node, ifToo large a value will affect the calculation efficiency of the method, and quick selection cannot be realized. If it is notThe accuracy of an evaluation result can be influenced by excessively small values. Therefore, the text tests the series of different neighbor nodesImpact on click importance ranking. Due to the fact thatThe value of (A) is valid only within the range of the network diameter, so that only the value of (B) is validTests were carried out. Five strokes of different grades were selected as test subjects, and the results are shown in fig. 5. It can be seen that whenWhen the size is small, the importance ordering of strokes greatly fluctuates; when in useGreater than average shortest path4.601, strokes are no longer ordered in their importanceChange, so in this experiment5. This reveals an important kinetic phenomenon: when in useGreater than the average path lengthAt the same time, the relative importance between strokes does not change, which means that consistent selection results can be obtained by the present technique.
(2) In order to test the effectiveness and the applicability of the technology, the roads networks are constructed by selecting strokes with different proportions according to the proportion of the total number of the strokes, and visual comparison is carried out, wherein the selection effect of 10%, 20%, 30% and 40% of the selection proportions is shown in fig. 6. It can be seen that:
On the premise of not using semantic information, the coverage range and the whole structure of the original road network are maintained under different selection proportions;
along with the increase of the selection proportion, the detail degree of the road network is increased step by step, and certain hierarchy is embodied;
the road networks under different selection proportions all reflect the density distribution characteristics of the original road networks.
(3) Further taking 30% as an example, inviting professional cartographers to select according to the traditional road selection rule, namely keeping the characteristics of the road network plane graph, keeping the connection between the road and the residential area and ensuring the selection of important roads. The result pairs of manual and automatic selection are shown in fig. 7. It can be seen that: the results of the two selection methods are integrally consistent; due to the effect of the "edge effect", the centrality values of the high-ranked roads located at the edge of the road network are low, so that they are not preferentially retained.
The maximum similarity and its related parameters are used to quantitatively analyze the two selection modes. The comparative statistical results are shown in table 1, and it can be seen that the selection effect of the technology has higher consistency with manual selection.
TABLE 1 maximum similarity and associated parameter statistics
Drawings
FIG. 1: two expression modes of road network
FIG. 3: selected strokes connectivity preservation
FIG. 4: lanzhou city gate area generalized road network
FIG. 5: stroke ordering (rank) for different range neighbor node sets (range)
FIG. 6: selection effect graph based on stroke quantity percentage
FIG. 7: and comparing the automatic selection result with the manual selection result.
Claims (1)
1. Road automatic selection technology based on gravitational field theory
A road automatic selection technology for considering influence of multi-level neighbor nodes of a road network dual graph by utilizing a gravitational field theory is characterized in that: firstly, generating a road network dual graph by means of strokes; then, calculating the centrality measurement value of the nodes by adopting a centrality method, regarding the centrality measurement value as mass, regarding the shortest distance between the nodes as distance, evaluating the importance of strokes by utilizing a Newton gravity formula, and constructing a road network by selecting the strokes with the importance ranking in the front; and finally, connectivity maintenance is carried out by defining the weight of the edge in the dual graph of the selected road network, so that automatic road selection is realized.
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