AU2021102429A4 - Method for selecting roads in a small-mesh accumulation area - Google Patents
Method for selecting roads in a small-mesh accumulation area Download PDFInfo
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- 230000008030 elimination Effects 0.000 claims abstract description 26
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- 238000004422 calculation algorithm Methods 0.000 claims abstract description 6
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F30/00—Computer-aided design [CAD]
- G06F30/10—Geometric CAD
- G06F30/18—Network design, e.g. design based on topological or interconnect aspects of utility systems, piping, heating ventilation air conditioning [HVAC] or cabling
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Abstract
OF THE DISCLOSURE
The present disclosure discloses a method for selecting roads in a small-mesh
accumulation area which is applied to the technical field of geographic mapping.
Starting meshes are redefined by simultaneously considering edge characteristics and
mesh density of the small meshes, and the starting meshes are changed into a pair of
adjacent small meshes from one small mesh. Problems that it is very difficult to control
a result of mesh elimination and it is very easy to change a spatial distribution structure
of a raw road network due to a fact that the starting mesh is located in the middle of the
small-mesh accumulation area are solved. Meanwhile, arc segments are eliminated on
the basis of a stroke connection sequence so that a spatial structure loss caused by some
remaining strokes is avoided. According to the method, the accumulating small-mesh
area in the road network is reasonably selected, thereby ensuring the integrity and
connectivity of roads in the area after synthesis.
-Page 1/14
Identifying small-mesh accumulation areas according to raw road network data, and
placing the small-mesh accumulation areas into a candidate set to be processed
Selecting a small-mesh accumulation area
Determining a starting mesh pair according to the small-mesh
accumulation area
Deleting the shared arc segment of the starting mesh pair, identifying the road stroke
where the shared are segment is located, sequentially identifying mesh pairs taking the
-P arc segment of the stroke as the shared arc segment according to the stroke connection
direction, deleting the shared are segment at the same time, completing the road
elimination of the corresponding mesh pair, and marking the newly generated mesh
Identifying a new starting mesh pair in a small-mesh accumulation area without
considering the newly generated mesh in S4
YES
Completing the road network selection
Calculating the density of newly generated meshes after the road network
selection, and re-identifying the small meshes in the accumulation area
Judging wh YES
newly generated mesh densities are
less than the mesh density
threshold
NO
Judging whether
NO there are only two adjacent
small meshes
NO
Judging whether there
is only one adjat small meshYE
YES Deleting the shared are segment of two adjacent small meshes,
calculating the mesh density
Deleting the
shared are segment of two adjacent
small meshes, calculating the mesh density, and judging
hether the mesh density is greater than th NO
mesh density threshold
YES
Carrying out road elimination on the isolated small mesh according
to a mesh elimination algorithm
Ending the road selection of the accumulation area
Juging
ether the selection of all
small-me .NO
accumulation areas
ends
YES
Copeigthe road selection of all small-mesh accumulation areas in the candidate set
FIG. 1
Description
-Page 1/14
Identifying small-mesh accumulation areas according to raw road network data, and placing the small-mesh accumulation areas into a candidate set to be processed
Selecting a small-mesh accumulation area
Determining a starting mesh pair according to the small-mesh accumulation area
Deleting the shared arc segment of the starting mesh pair, identifying the road stroke where the shared are segment is located, sequentially identifying mesh pairs taking the -P arc segment of the stroke as the shared arc segment according to the stroke connection direction, deleting the shared are segment at the same time, completing the road elimination of the corresponding mesh pair, and marking the newly generated mesh
Identifying a new starting mesh pair in a small-mesh accumulation area without considering the newly generated mesh in S4
Completing the road network selection
Calculating the density of newly generated meshes after the road network selection, and re-identifying the small meshes in the accumulation area
Judging wh YES newly generated mesh densities are less than the mesh density threshold
Judging whether NO there are only two adjacent small meshes NO Judging whether there is only one adjat small meshYE
YES Deleting the shared are segment of two adjacent small meshes, calculating the mesh density
Deleting the shared are segment of two adjacent small meshes, calculating the mesh density, and judging hether the mesh density is greater than th NO mesh density threshold
YES Carrying out road elimination on the isolated small mesh according to a mesh elimination algorithm
Ending the road selection of the accumulation area
Juging all small-me .NO ether the selection ofareas accumulation ends YES
Copeigthe road selection of all small-mesh accumulation areas in the candidate set
FIG. 1
[01] The present disclosure relates to the technical field of geographic mapping, in particular to a method for selecting roads in a small-mesh accumulation area.
[02] The road network on the map is an objective construction of the connectivity and distribution of the road network in the real geographical world, and is the skeleton element of the map. Usually, the road network has many grades, complex relationships and network-like. Therefore, how to realize the multi-scale continuous expression of the road network is always a difficult problem. Road network is connected with each other by various road segments and forms a series of meshes. When multi-scale continuous expression is carried out, it is necessary to scientifically eliminate the meshes of road network, so as to ensure that multi-scale expression can not only maintain the connectivity and integrity of the road itself, but also accurately reflect the spatial shape of the road and the density characteristics of the road network.
[03] Road network is one of the main infrastructure elements in various scale maps. In order to obtain continuous multi-scale spatial representation, road network often needs map synthesis, and the key core of synthesis lies in how to select reasonable roads, so as to retain important roads, eliminate secondary roads, and maintain the spatial characteristics and network structure of roads, as well as the basic semantic, topological and geometric characteristics of roads.
[04] Under these constraints, how to effectively maintain the spatial distribution structure of road network is a difficult point. Therefore, scholars at home and abroad have done a lot of research on the structure selection of road network in recent years. For example, Hu Yungang et al. put forward a method for selecting roads based on network mesh density, which deletes all the small meshes whose mesh density exceeds the threshold value in sequence, and deletes the least important road segment in each small mesh. The result can effectively reflect the overall characteristics of the road network and the local density changes in different areas. Therefore, it is often used to complete the road network selection in dense road areas. The research of Li Zhilin et al. shows that this method has the best effect for selecting road segments across one or two meshes. Wei Wu and Touya have applied the mesh-based method to urban road selection and have achieved good results. However, the existing methods are suitable for most isolated small-mesh road areas on the map, but there are still some accumulated small meshes in residential districts or large factories. The existing mesh-based method for selecting roads will destroy the typical spatial characteristics of roads in such areas. Although there are few small-mesh accumulation areas on the map, unreasonable selection will still affect the overall quality of road selection to a certain extent.
[05] Therefore, it is an urgent problem for those skilled in the art about how to provide a method for selecting roads in a small-mesh accumulation area, which reasonably selects small-mesh accumulation areas in the road network, thereby ensuring the integrity and connectivity of roads in this area after synthesis.
[06] In view of this, the present disclosure provides a method for selecting roads in a small-mesh accumulation area, which reasonably selects small-mesh accumulation areas in the road network, thereby ensuring the integrity and connectivity of roads in this area after synthesis.
[07] In order to achieve the above purpose, the present disclosure adopts the following technical scheme.
[08] A method for selecting roads in a small-mesh accumulation area, comprising the specific steps of:
[09] S1, identifying small-mesh accumulation areas according to raw road network data, and placing the small-mesh accumulation areas into a candidate set to be processed;
[10] S2, selecting a small-mesh accumulation area;
[11] S3, determining a starting mesh pair according to the small-mesh accumulation area;
[12] S4, deleting the shared arc segment of the starting mesh pair, identifying the road stroke where the shared arc segment is located, sequentially identifying mesh pairs taking the arc segment of the stroke as the shared arc segment according to the stroke connection direction, deleting the shared arc segment at the same time, completing the road elimination of the corresponding mesh pair, and marking the newly generated mesh;
[13] S5, identifying a new starting mesh pair in a small-mesh accumulation area without considering the newly generated mesh in S4;
[14] S6, repeating S4-S5 until no new starting mesh pair is found, and completing the road network selection;
[15] S7, calculating the density of newly generated meshes after the road network selection, and re-identifying the small meshes in the accumulation area;
[16] S8, repeating S3-S7 until all newly generated mesh densities are less than the mesh density threshold, and executing S11; otherwise, judging that there are only two adjacent small meshes in the accumulation area, and executing S9; otherwise, judging the number of adjacent small meshes, when there is only one, executing S10; when there are more than 2, executing S3;
[17] S9, deleting the shared arc segment of two adjacent small meshes, calculating the mesh density, and if the mesh density is greater than the mesh density threshold, executing S10; if the mesh density is less than the mesh density threshold, executing S12;
[18] S10, carrying out road elimination on the isolated small mesh according to a mesh elimination algorithm;
[19] S11, completing the road selection of the accumulation area;
[20] S12, repeating S2-S11 until the roads of all small-mesh accumulation areas in the candidate set are selected.
[21] Preferably, in the above method for selecting roads in a small-mesh accumulation area, the specific steps in S Iare as follows:
[22] constructing a node-arc segment-polygon topology for raw road network data, wherein the closed area corresponding to the topology polygon is a mesh;
[23] calculating the density of each mesh in the road network, determining the threshold of the mesh density by using a sample map statistical method, regarding the mesh whose mesh density exceeds the threshold as a small mesh, and building road Stroke at the same time;
[24] traversing all the small meshes of the road network, and identifying the small-mesh accumulation area, that is, the road area where the number of adjacent small meshes is 32; and placing the small-mesh accumulation area into a candidate set to be processed.
[25] Preferably, in the above method for selecting roads in a small-mesh accumulation area, in S3, the adjacency relationship between two small meshes is calculated according to the node arc polygon topology, and it is judged that the two small meshes are adjacent to each other; and at the same time, according to the topological structure of the small mesh, the boundary of each accumulation area is extracted and taken as a hard constraint;
[26] at the same time, considering the edge characteristics and the mesh density of small meshes, the starting mesh is defined, and two adjacent small meshes located at the edge of the accumulation area and with the smallest sum of the mesh density are taken as a starting mesh pair.
[27] Preferably, in the above method for selecting roads in a small-mesh accumulation area, the mesh density threshold calculation method compares mesh density distribution curves of two scales before and after synthesis of the road network (the scale before synthesis is larger than the scale after synthesis), and takes corresponding values of split nodes with obviously different curves as density thresholds.
[28] According to the above technical scheme, compared with the prior art, the present disclosure provides a method for selecting roads in a small-mesh accumulation area, which reasonably selects small-mesh accumulation areas in the road network, thereby ensuring the integrity and connectivity of roads in this area after synthesis. According to the present disclosure, starting meshes are redefined by simultaneously considering edge characteristics and mesh density of the small meshes, and the starting meshes are changed into a pair of adjacent small meshes from one small mesh. Problems that it is very difficult to control a result of mesh elimination and it is very easy to change a spatial distribution structure of a raw road network due to a fact that the starting mesh is located in the middle of the small-mesh accumulation area are solved. Meanwhile, arc segments are eliminated on the basis of a stroke connection sequence so that a spatial structure loss caused by some remaining strokes is avoided.
[29] In order to explain the embodiments of the present disclosure or the technical scheme in the prior art more clearly, the drawings needed in the embodiments will be briefly introduced hereinafter. Obviously, the drawings in the following description are only some embodiments of the present disclosure. For those skilled in the art, other drawings can be obtained according to these drawings without paying creative labor.
[30] FIG. 1 is a flow chart of the method according to the present disclosure;
[31] FIG. 2(a) is a schematic diagram of defining a first-order neighborhood of a mesh in a starting mesh pair with a density of 0.42 according to an embodiment of the present disclosure;
[32] FIG. 2(b) is a schematic diagram of defining a first-order neighborhood of a mesh in a starting mesh pair with a density of 0.38 according to an embodiment of the present disclosure;
[33] FIG. 2(c) is a schematic diagram of a new round of starting mesh pairs;
[34] FIG. 3(a) is a schematic diagram of strokes for starting mesh pairs and their shared arc segments according to an embodiment of the present disclosure;
[35] FIG. 3(b) is a schematic diagram of an elimination result based on a stroke connection sequence;
[36] FIG. 3(c) is a schematic diagram of an elimination result (a descending order) based on a mesh density method;
[37] FIG. 4(a) is afirst schematic diagram of iterative identification and processing of starting mesh pairs according to an embodiment of the present disclosure, wherein the starting mesh (orange) and related stroke (red) in the first round are shown;
[38] FIG. 4(b) is a second schematic diagram of iterative identification and processing of starting mesh pairs according to an embodiment of the present disclosure, wherein the selection results (orange) in the first round and newly formed mesh are shown;
[39] FIG. 4(c) is a third schematic diagram of iterative identification and processing of starting mesh pairs according to an embodiment of the present disclosure, in which starting mesh pairs (blue) and related stroke (red) in the second round are shown;
[40] FIG. 4(d) is a fourth schematic diagram of iterative identification and processing of starting mesh pairs according to an embodiment of the present disclosure, which is the final selection result;
[41] FIG. 5 is a data diagram used in the experiment according to an embodiment of the present disclosure;
[42] FIG. 6 is a graph of shape similarity results obtained by processing an accumulation area containing two small meshes by two comparison methods according to an embodiment of the present disclosure;
[43] FIG. 7(a) is a schematic diagram of the processing result of a first typical area by a first method in an accumulation area containing two small meshes according to an embodiment of the present disclosure;
[44] FIG. 7(b) is a schematic diagram of the processing result of a first typical area by a method of the present disclosure in an accumulation area containing two small meshes according to an embodiment of the present disclosure;
[45] FIG. 7(c) is a schematic diagram of the processing result of a second typical area by a first method in an accumulation area containing two small meshes according to an embodiment of the present disclosure;
[46] FIG. 7(d) is a schematic diagram of the processing result of a second typical area by a method of the present disclosure in an accumulation area containing two small meshes according to an embodiment of the present disclosure;
[47] FIG. 8(a) is a schematic diagram of the shape similarity results obtained by processing an accumulation area containing more than two small meshes by two comparison methods according to an embodiment of the present disclosure;
[48] FIG. 8(b) is a schematic diagram of the results of the area variation coefficient obtained by processing an accumulation area containing more than two small meshes by two comparison methods according to an embodiment of the present disclosure;
[49] FIG. 9(a) is a schematic diagram of the processing result of a first typical area by a first method in a typical accumulation area containing more than two small meshes according to an embodiment of the present disclosure;
[50] FIG. 9(b) is a schematic diagram of the processing result of a first typical area by a method of the present disclosure in a typical accumulation area containing more than two small meshes according to an embodiment of the present disclosure;
[51] FIG. 9(c) is a schematic diagram of the processing result of a second typical area by a first method in a typical accumulation area containing more than two small meshes according to an embodiment of the present disclosure;
[52] FIG. 9(d) is a schematic diagram of the processing result of a second typical area by a method of the present disclosure in a typical accumulation area containing more than two small meshes according to an embodiment of the present disclosure;
[53] FIG. 9(e) is a schematic diagram of the processing result of a third typical area by a first method in a typical accumulation area containing more than two small meshes according to an embodiment of the present disclosure;
[54] FIG. 9(f) is a schematic diagram of the processing result of a third typical area by a method of the present disclosure in a typical accumulation area containing more than two small meshes according to an embodiment of the present disclosure.
[55] The technical scheme in the embodiments of the present disclosure will be described clearly and completely hereinafter with reference to the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only some embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by those skilled in the art without paying creative labor belong to the scope of protection of the present disclosure.
[56] As shown in FIG. 1, the embodiment of the present disclosure provides a method for selecting roads in a small-mesh accumulation area, comprising the steps of:
[57] S1, identifying small-mesh accumulation areas according to raw road network data, and placing the small-mesh accumulation areas into a candidate set to be processed;
[58] S101, constructing a node-arc segment-polygon topology for raw road network data, wherein the closed area corresponding to the topology polygon is a mesh;
[59] S102, calculating the density of each mesh in the road network, determining the threshold of the mesh density by using a sample map statistical method, and defining the mesh whose mesh density exceeds the threshold as a small mesh;
[60] S103, traversing all the small meshes of the road network, and identifying the small-mesh accumulation area, that is, the road area where the number of adjacent small meshes is 32; and placing the accumulation areas into a candidate set to be processed.
[61] S2, selecting a small-mesh accumulation area;
[62] S3, determining a starting mesh pair according to the small-mesh accumulation area;
[63] S4, deleting the shared arc segment of the starting mesh pair, identifying the road stroke where the shared arc segment is located, sequentially identifying mesh pairs taking the arc segment of the stroke as the shared arc segment according to the stroke connection direction, deleting the shared arc segment at the same time, completing the road elimination of the corresponding mesh pair, and marking the newly generated mesh;
[64] S5, identifying a new starting mesh pair in a small-mesh accumulation area without considering the newly generated mesh in S4;
[65] S6, repeating S4-S5 until no new starting mesh pair is found, and completing the road network selection;
[66] S7, calculating the density of newly generated meshes after the road network selection, and re-identifying the small meshes in the accumulation area;
[67] S8, repeating S3-S7 until all newly generated mesh densities are less than the mesh density threshold, and executing S11; otherwise, judging that there are only two adjacent small meshes in the accumulation area, and executing S9; otherwise, judging the number of adjacent small meshes, when there is only one, executing S1O; when there are more than 2, executing S3;
[68] S9, deleting the shared arc segment of two adjacent small meshes, calculating the mesh density, and if the mesh density is greater than the mesh density threshold, executing S10; if the mesh density is less than the mesh density threshold, executing S12;
[69] S10, carrying out road elimination on the isolated small mesh according to the existing mesh elimination algorithm;
[70] S11, completing the road selection of the accumulation area;
[71] S12, repeating S2-S11 until the roads of all small-mesh accumulation areas in the candidate set are selected.
[72] Further, in step S102, the mesh density threshold calculation method compares mesh density distribution curves of two scales before and after synthesis of the road network, and takes corresponding values of split nodes with obviously different curves as density thresholds. For example, 0.016m/m 2 is considered as the mesh density threshold for converting from 1:10000 to 1:50000 urban road network. The mesh whose mesh density greater than the threshold is defined as a small mesh.
[73] Further, in step S103, according to the number of adjacent small meshes, the road network is divided into three types of areas: 1) a small-mesh accumulation area with two or more adjacent small meshes; 2) an isolated area of a small mesh, in which there is only one small mesh and no adjacent small mesh; 3) other areas without small meshes.
[74] Further, the adjacency relationship between two small meshes is calculated according to the node arc polygon topology. Two small meshes (i.e., polygons) are considered to be adjacent to each other if they share a common arc segment. At the same time, according to the topological structure of the small mesh, the boundary of each accumulation area is extracted and taken as a hard constraint, that is, the boundary is directly retained, and the boundary is not eliminated in the elimination process.
[75] As shown in FIG. 2, the embodiment is directed to the selection of starting mesh pairs in step S3.
[76] For the commonly used mesh-based method, the small mesh with the highest mesh density is selected as the initial mesh. If the starting mesh is located in the middle of the small-mesh accumulation area, it is difficult to control the result of mesh elimination, and it is easy to change the spatial distribution structure of the raw road network. Therefore, the embodiment of the present disclosure redefines the starting mesh by simultaneously considering the edge characteristics and the mesh density of the small mesh, and changes the starting mesh from one small mesh to a pair of adjacent small meshes.
[77] According to the embodiment of the present disclosure, the starting meshes in which the mesh is eliminated are redefined as two adjacent meshes, in which the sum of the mesh densities is the largest. The starting meshes are located at the outermost layer of the accumulation area. According to the embodiment of the present disclosure, the first-order neighborhood of the small mesh is introduced for the starting mesh. For a small mesh, the first-order neighborhood is formed by neighboring small meshes that share common segments or nodes therewith. Obviously, the number of small meshes at the boundary is the least in the first-order neighborhood.
[78] As shown in FIG. 2(a), for a mesh with a density of 0.42 (blue), the first-order neighborhood is a mesh with densities of 0.40, 0.38 and 0.28 (pink), and the number of small meshes in the first-order neighborhood is 3. Similarly, in FIG. 2(b), for a mesh with a density of 0.38 (blue), the first-order neighborhood comprises meshes with densities of 0.42, 0.40, 0.28, 0.26 and 0.34 (pink), and the number is 5. Therefore, the mesh with a density of 0.42 is closer to the network edge than the mesh with a density of 0.38. In addition, small mesh pairs formed by meshes with densities of 0.42 and 0.40 (orange) have the largest total mesh density, and these meshes are selected as starting meshes, as shown in FIG. 2(c).
[79] As shown in FIG. 3, the embodiment explains the arc segment elimination in step S4.
[80] For the starting mesh in S3, the shared arc segment between meshes is marked. Then, the stroke where the shared arc segment is located is identified, and other mesh pairs sharing other arc segments in the stroke are determined. The arc elimination process used in this method is the stroke connection sequence. The advantage of this method is to avoid the spatial structure loss caused by some remaining strokes. As shown in FIG. 3(a), the meshes with densities of 0.42 and 0.40 (orange) are defined as starting mesh pairs, and the stroke where their shared arc segment is located is marked. In this stroke, other mesh pairs sharing other road segments are eliminated in sequence, and the elimination result is shown in FIG. 3(b). FIG. 3(c) shows the elimination result considering the mesh density in a descending order proposed by Hu Yungang et al. It can be seen that the raw spatial structure of a small mesh is destroyed.
[81] As shown in FIG. 4, a new starting mesh pair is identified without considering the newly formed mesh obtained in step S6. As shown in FIG. 4(a), two adjacent orange small meshes are the starting mesh pairs in the first round, and the newly formed mesh (orange in FIG. 4(b)) will not participate in the identification of the starting mesh in the second round. Therefore, as shown in FIG. 4(c), the two adjacent small meshes displayed in blue are the starting meshes of the second round, and the final selection result is shown in FIG. 4(d).
[82] As shown in FIG. 5-FIG. 9, it is an experiment conducted in the embodiment to verify the reliability and superiority of the method of the present disclosure.
[83] FIG. 5 is the experimental data, which is the raw road data in a 1:10000 topographic map of a certain area in Jiangsu Province. The spatial range of the data is 23.91x18.67km 2, and the comprehensive target scale is 1:50000. The mesh density threshold is set to 0.016m/m 2 in a ratio of 1:50000.
[84] There are 1782 meshes in the experimental area, containing 471 small meshes and 1311 non-small meshes. Detailed classification of 471 small meshes is shown in Table 1. 23.77% of the small meshes are isolated small meshes, and the remaining small meshes form 64 accumulation areas. Therefore, the small meshes in the experimental area have obvious accumulation characteristics. In the accumulation area of small meshes, the minimum number of small meshes is 2, which indicates that two adjacent small meshes need to form an accumulation area. The largest accumulation area consists of 47 small meshes.
[85] Table 1 Detailed classification of small meshes in experimental area
isolated accumulation of small meshes small meshes
64 accumulation areas (containing 359 small meshes)
The number of small meshes in an accumulation area
112 the the theaverage minimum maximum number number number
2 47 5.6
[86] In order to verify the effect of the method of the present disclosure, two methods are adopted to conduct comparative experiments: one method is the mesh-based method proposed by Hu Yungang to process all meshes, and the other method is to process isolated small meshes by the mesh-based method proposed by Hu Yungang, and to process accumulating meshes by the method proposed by the present disclosure. For 112 isolated small meshes, because the two comparison methods are mesh-based elimination methods, the results are the same. The embodiment mainly describes the elimination of accumulating meshes.
[871 For 32 accumulation areas consisted of 2 small meshes, 10 areas with the same results are produced by the two comparison methods, accounting for 31.25% of all accumulation areas. However, the number of areas with large differences in selection results is 22, accounting for 68.75% of all accumulation areas. The selection results are quantitatively evaluated by shape similarity (SS). The formula of shape similarity is as follows:
SS = BArea; 1881 =n AAreai
[89] where n represents the total number of meshes related to the accumulation area, i is the i-th small mesh, BAreat represents the area of the i-th small mesh before selection, and AAreai represents the area of the mesh containing the raw i-th small mesh after selection. Obviously, when SS value is 1, the road mesh shape similarity before and after the selection result is optimal.
[901 Through calculation, the SS results obtained by the two comparison methods are shown in FIG. 6. The SS values of 10 accumulation areas with the same selection results are all 1, and the shape characteristics of these meshes have not changed. However, the SS values of the other 22 clusters are significantly different. For example, in the first accumulation area containing two small meshes, the minimum value of SS is 0.01 by the first method, which means that one (or two) of the two small meshes in this area is merged into a very large adjacent mesh, and the area of the raw small mesh has changed greatly. The SS values corresponding to the second method (the method of the present disclosure) are all 1, which indicates that two small meshes can form a new mesh whose mesh density meets the threshold. Similar situations occur in other 21 accumulation areas. Therefore, the method of the present disclosure has less influence on the spatial structure of the road network, and can better retain local characteristics.
[911 FIG. 7 shows two typical accumulation areas with the same selection result and different results, and the results obtained by two comparison methods. It can be seen from FIG. 7(a) and FIG. 7(b) that for the first typical area, the selection results of the two different methods are the same, and the least important part of the small mesh is the common part a. However, as shown in FIG. 7(c) and FIG. 7(d), the least important part in the mesh is not always the common part a. Therefore, the two methods produce different selection results for the second typical area. Intersecting with the first method, the selection result generated by the method of the present disclosure better keeps the compact structure of small meshes and keeps the connectivity of the road stroke where the road segment b is located.
[92] For 32 accumulation areas consisted of more than two small meshes, the selection results are quantitatively evaluated by shape similarity (SS) and area variation coefficient (CVA). The formula of CVA is as follows:
CVA = area
[931 Parea
[941 Garea represents the standard deviation of the area of small meshes in the accumulation area, and area is the average area of small meshes in the accumulation area. CVA is used to measure the uniformity of meshes in accumulation area. The smaller the CVA value is, the more uniform the area distribution is. FIG. 8 shows SS and CVA of two methods in each accumulation area.
[95] As shown in FIG. 8(a), the range of SS values of 32 accumulation areas obtained by the first method is [0.03, 0.78], which indicates that the areas of all small meshes have changed in different degrees. In contrast, the SS values of these accumulation areas obtained by the method of the present disclosure are all 1, and the boundary constraints ensure that the spatial structure of the raw accumulation areas will generally not change. As shown in FIG. 8(b), compared with the CVA values of the raw accumulation areas, the CVA values of 27 accumulation areas obtained by the method of the present disclosure decrease, while the values of 26 accumulation areas obtained by the first method increase, indicating that the density distribution of the results of the method of the present disclosure is more uniform than that of the first method.
[96] FIG. 9 shows 32 types of accumulation areas consisted of more than 2 small meshes, and three typical accumulation areas in which the minimum (3), median (8) and maximum (47) meshes are selected, and the results obtained by two comparison methods. It can be found that in FIG. 9(a) and FIG. 9 (b), for the first typical area (with the minimum number of small meshes), the first method eliminates road segments a, b and c according to the low importance of road segments, which greatly changes the spatial structure of the road network in this area. In contrast, the method of the present disclosure considers boundary constraints and eliminates isolated roads stroke a and d. The selection result better reflects the road network structure. In FIGS. 9(c) and 9 (d), for the second typical area (the median number of small meshes), the first method eliminates road segments a, b, c, d, h and g located in four different strokes, and the result is poor. In contrast, the method of the present disclosure uses an arc segment sequential identification and elimination algorithm, which only eliminates two road strokes (one stroke is formed by segments a and b and the other stroke is formed by segments e, f and g) in the accumulation area, and the obtained result is more reasonable. In FIGS. 9(e) and 9 (f), for the third typical area (the maximum number of small meshes), compared with the first method, the method of the present disclosure can better maintain the mesh distribution density. There are obvious differences between the selection results of these two methods in the areas where strokes are located on the three roads Si, S2 and S3. The maintenance of SIhas an important impact on the uniformity of distribution density, and a clear outline can be obtained by the maintenance of strokeS3. In addition, the method of the present disclosure completely retains strokeS2, which better reflects road connectivity.
[97] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. It is sufficient to refer to the same and similar parts among each embodiment. For the device disclosed in the embodiment, because it corresponds to the method disclosed in the embodiment, it is described relatively simply, and the relevant points can be found in the description of the method.
[98] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present disclosure. Many modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure should not be limited to the embodiments shown herein, but should conform to the widest scope consistent with the principles and novel features disclosed herein.
Claims (4)
1. A method for selecting roads in a small-mesh accumulation area, comprising the specific steps of:
Si, identifying small-mesh accumulation areas according to raw road network data, and placing the small-mesh accumulation areas into a candidate set to be processed;
S2, selecting a small-mesh accumulation area;
S3, determining a starting mesh pair according to the small-mesh accumulation area;
S4, deleting the shared arc segment of the starting mesh pair, identifying the road stroke where the shared arc segment is located, sequentially identifying mesh pairs taking the arc segment of the stroke as the shared arc segment according to the stroke connection direction, deleting the shared arc segment at the same time, completing the road elimination of the corresponding mesh pair, and marking the newly generated mesh;
S5, identifying a new starting mesh pair in a small-mesh accumulation area without considering the newly generated mesh in S4;
S6, repeating S4-S5 until no new starting mesh pair is found, and completing the road network selection;
S7, calculating the density of newly generated meshes after the road network selection, and re-identifying the small meshes in the accumulation area;
S8, repeating S3-S7 until all newly generated mesh densities are less than the mesh density threshold, and executing S11; otherwise, judging that there are only two adjacent small meshes in the accumulation area, and executing S9; otherwise, judging the number of adjacent small meshes, when there is only one, executing S10; when there are more than 2, executing S3;
S9, deleting the shared arc segment of two adjacent small meshes, calculating the mesh density, and if the mesh density is greater than the mesh density threshold, executing S10; if the mesh density is less than the mesh density threshold, executing S12;
S10, carrying out road elimination on the isolated small mesh according to a mesh elimination algorithm;
Sib, completing the road selection of the accumulation area;
S12, repeating S2-SiIuntil the roads of all small-mesh accumulation areas in the candidate set are selected.
2. The method for selecting roads in a small-mesh accumulation area according to claim 1, wherein the specific steps in Si are as follows:
constructing a node-arc segment-polygon topology for raw road network data, wherein the closed area corresponding to the topology polygon is a mesh;
calculating the density of each mesh in the road network, determining the threshold of the mesh density by using a sample map statistical method, regarding the mesh whose mesh density exceeds the threshold as a small mesh, and building road Stroke at the same time;
traversing all the small meshes of the road network, and identifying the small-mesh accumulation area, that is, the road area where the number of adjacent small meshes is 32; and placing the small-mesh accumulation area into a candidate set to be processed.
3. The method for selecting roads in a small-mesh accumulation area according to claim 2, wherein in S3, the adjacency relationship between two small meshes is calculated according to the node arc polygon topology, and it is judged that the two small meshes are adjacent to each other; and at the same time, according to the topological structure of the small mesh, the boundary of each accumulation area is extracted and taken as a hard constraint;
at the same time, considering the edge characteristics and the mesh density of small meshes, the starting mesh is defined, and two adjacent small meshes located at the edge of the accumulation area and with the smallest sum of the mesh density are taken as a starting mesh pair.
4. The method for selecting roads in a small-mesh accumulation area according to claim 2, wherein the mesh density threshold calculation method compares mesh density distribution curves of two scales before and after synthesis of the road network, and takes corresponding values of split nodes with obviously different curves as density thresholds.
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