Rail section traversal method, device and medium based on depth-first search algorithm

Abstract

The application relates to a track section traversal method, device and medium based on a depth-first search algorithm, which adopts a backtracking method to prune invalid paths and adopts a memory method to mark track sections that have been processed. Compared with the prior art, the application has the advantages of real-time efficiency and the like.

Description

Technical Field

[0001] This invention relates to train signal control systems, and more particularly to a method, device, and medium for traversing track sections based on a depth-first search algorithm. Background Technology

[0002] Electronic map data for urban rail transit systems records information such as hardware equipment and track segment divisions throughout the entire line. Communication-based train control systems read this electronic map data to obtain real-time positioning information and implement safety control measures for train speed. The track segment topology of urban rail transit systems is analogous to a graph data structure, and common traversal methods include Depth-First Search (DFS) and Breadth-First Search (BFS). BFS prioritizes searching for the shortest path from the start to the end of the line, offering fast search speeds for such scenarios but consuming significant memory. DFS uses a stack-based storage method, searching in a single direction, prioritizing the search direction when encountering a switch, continuing until the end of the line, then returning to the switch position to continue searching downstream. Complete paths already searched are not retained, saving storage space. Due to the large topological depth, numerous branches, and complex structure of track segments in electronic map data, DFS is superior to BFS for solving all objective solutions for the entire line.

[0003] A search revealed that Chinese patent CN113672690A discloses a method for traversing track segments. Specifically, it discloses a data structure for constructing a graph using vertex sets, edge sets, and basic operations between vertices and edges. The method iterates through track segments, mapping each segment to a vertex and the connections between segments to edges. Based on the graph data structure, a topological structure graph of the track segments is constructed. Based on this graph, a depth-first search algorithm or a breadth-first search algorithm is applied to provide a general traversal method for track segments, enabling the traversal of track segments.

[0004] However, while Depth-First Search (DFS) saves memory, it can lead to repeated searches, resulting in low search efficiency and slow execution speed. Therefore, improving the DFS algorithm to increase its efficiency is a technical problem that needs to be solved. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art by providing a real-time and efficient method, device and medium for traversing track segments based on a depth-first search algorithm.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] According to a first aspect of the present invention, a method for traversing track segments based on a depth-first search algorithm is provided. This method uses backtracking to prune invalid paths and uses memoization to mark track segments that have already been processed.

[0008] As a preferred technical solution, the method specifically includes the following steps:

[0009] Step S1: Parameter initialization. Obtain all path search starting points in the electronic map and use the depth-first search algorithm to search downstream from the path starting point.

[0010] In step S2, if a pruning marker is encountered, the search is stopped and the search is backtracked to other branches that have not been searched to continue the depth-first traversal search.

[0011] Step S3: If the searched track segment has been processed and meets the condition that the downstream search no longer needs to continue, then stop the search; if the searched track segment has not been processed, then mark it as processed and continue searching downstream.

[0012] Step S4: If the end of the track is found, stop the search and backtrack upstream from the end of the track to prune invalid paths and mark the pruning points on the corresponding track segments.

[0013] Step S5: If all the starting points of the path search in step S1 have been traversed, then the search is complete.

[0014] As a preferred technical solution, the starting point for path search in step S1 is specifically:

[0015] If there are no other connected track segments upstream of this track segment, then this track segment will be used as the starting point to search downstream.

[0016] As a preferred technical solution, the step S1 of using a depth-first search algorithm to search downstream from the path starting point specifically involves:

[0017] First, start the search from the starting point and search in a single direction. When a turnout is encountered, prioritize searching to locate the direction. Continue searching until the end of the line. Then, according to the stack first-in-last-out principle, retreat to the track section where the turnout is reversed and continue searching downstream.

[0018] As a preferred technical solution, the pruning mark in step S2 is specifically a mark indicating whether the downstream of the track segment needs to be searched. If a pruning mark is found, the search stops and the search returns to other branches that have not been searched.

[0019] As a preferred technical solution, step S3, marking whether the track segment has been processed, specifically involves:

[0020] An optimization method using memory search is employed. If a track segment has already been processed and meets the condition that no further downstream search is required, the search is terminated early. Any processed track segment is marked as processed.

[0021] As a preferred technical solution, in step S3, the condition that no downstream search is required is met, and the judgment is made according to the algorithm for generating the target solution.

[0022] As a preferred technical solution, in step S4, tracing back upstream from the end of the track to prune invalid paths specifically involves:

[0023] If the target solution is encountered during the backtracking process, a pruning mark is placed on the first track segment downstream of the target solution;

[0024] If a convergence node is encountered during the backtracking process, a pruning mark is placed on that track segment; if both the positioning branch and the reverse branch have pruning marks placed on their track segments, the two branches are merged, and the backtracking continues upstream from that convergence node.

[0025] If the end of a track is encountered during the backtracking process, a pruning mark is placed on that track segment.

[0026] As a preferred technical solution, in step S4, during the backtracking process from the end of the track upstream, the DFS algorithm is used. If a turnout is encountered, the turnout location branch is traversed first until the end of the track is found, at which point the search of that branch is stopped. Then, the reverse branches of the turnout are popped out of the stack in the order of last-in-first-out (LIFO) and searched accordingly. If an extreme point is encountered during the search, the search is reversed and the search continues.

[0027] As a preferred technical solution, in step S5, if the path search starting point in step S1 has been traversed and searched, then the search is completed; otherwise, continue searching downstream from the search starting point, performing a depth-first traversal according to the situations in steps S2, S3, and S4.

[0028] According to a second aspect of the present invention, an electronic device is provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the program to implement the method described thereon.

[0029] According to a third aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, implements the method described thereon.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] 1) This invention uses backtracking to prune invalid paths and memory to mark already processed track segments, reducing the traversal of invalid paths.

[0032] 2) According to actual results, the optimized method for traversing track segments provided by this invention has the characteristics of high operating efficiency. Combined with the storage-saving characteristics of the depth-first search algorithm, it can be used as an efficient traversal method for track segments in urban rail transit systems. Attached Figure Description

[0033] Figure 1 This is a flowchart illustrating the specific process of the method of the present invention;

[0034] Figure 2 The rules for generating Adjacent_SSA in this embodiment of the invention;

[0035] Figure 3 This is a DFS-based track segment traversal method in this embodiment of the invention;

[0036] Figure 4 This is a DFS track segment traversal method based on backtracking algorithm in an embodiment of the present invention;

[0037] Figure 5 This is a partial view of an actual circuit in an embodiment of the present invention. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0039] During train operation, the train needs to obtain the target distance between the current platform and the next target platform in real time. To improve the operating efficiency of the ATC system, the target distances between all pairs of platforms along the entire line can be calculated offline and stored in the ATO system's configuration data. The online software directly iterates through the Adjacent_ssa list in the configuration data to obtain the target distance information. The onboard offline software reads electronic map data and parses the Service_stopping_area (SSA) tags in the track section. If the SSA is associated with a Vital_passenger_exchange_zone (VPEZ), it needs to find the nearest downstream SSA that meets the same conditions based on the link relationship between the track section and the SSA, and generate the Adjacent_ssa list. The generation rules are as follows: Figure 2 As shown. Generating this list requires traversing all track sections along the entire line.

[0040] This invention takes solving all Adjacent_SSAs that meet the conditions in the entire line as an example to illustrate a specific implementation of an optimization method based on depth-first traversal of track segments.

[0041] DFS-based traversal methods for track segments, such as... Figure 3 As shown, the steps are as follows:

[0042] Step 1: Traverse all track segments in the electronic map data. If there is no upstream link for a track segment, it is the end of the starting track. Use this track segment as the starting point to search downstream.

[0043] Step 2: During the downstream search, for each track segment traversed, it is necessary to determine whether there is an SSA tag on that track segment and whether the SSA has an associated VPEZ tag.

[0044] If an SSA that satisfies the conditions exists in the traversed orbital segment, then:

[0045] (1) If the current SSA_Begin is empty, then assign a value to SSA_Begin and assign the distance from the coordinates of the SSA to the end of the track segment to the Distance variable, and then continue to search for SSAs that meet the conditions downstream.

[0046] (2) If the current SSA_Begin is not empty, SSA_Next is empty, and the SSA that meets the conditions does not belong to the same SSA as SSA_Begin, then assign a value to SSA_Next, generate an Adjacent_SSA(SSA_Begin, SSA_Next) element, and add it to the list. Then assign SSA_Next to SSA_Begin, clear SSA_Next, and assign the distance from the coordinates of this SSA to the end of the track segment to the Distance variable, and continue the search.

[0047] (3) If the current SSA that meets the conditions belongs to the same SSA region as SSA_Begin, then add Distance to the length of the current track segment and continue searching downstream for SSA_Next.

[0048] If no SSA satisfying the conditions is found in the traversed orbital segment, then:

[0049] (1) If SSA_Begin is not empty, add Distance to the length of the current track segment and continue searching downstream for SSA_Next;

[0050] (2) If SSA_Begin is empty, no operation is performed, and the search continues downstream for SSA_Begin that meets the conditions.

[0051] Step 3: If there is no track segment downstream of the track segment being traversed, that is, the end of the final track, or if a certain SSA is equal to the search starting SSA, that is, the path is a loop, then stop the search.

[0052] Step 4: During the downstream search, if a reversal point is encountered, the search direction is changed and the search continues; if a switch is encountered, the search is first performed using the positioning branch until the condition for stopping the search in Step 3 is met and the process returns. Then, following the last-in-first-out order of the stack, each track segment traversed is popped sequentially. If a switch exists, the search is performed downstream starting from the reverse branch.

[0053] Based on the depth-first search (DFS) traversal optimization method for track segments, a backtracking algorithm is added to perform feasibility pruning on invalid paths, such as... Figure 4 As shown, the specific steps are as follows:

[0054] Step A: In Step 3 of the DFS algorithm, if the traversed track segment is the end of the track and there is no track segment downstream, then backtrack upstream from the end of the track.

[0055] (1) If an SSA that meets the conditions is encountered, mark the first track segment downstream of the SSA with a sign that there is no valid SSA upstream or downstream, and stop the search.

[0056] (2) If no valid SSA is found, but a convergence node is found, mark the current orbital segment as having no valid SSA upstream or downstream and stop the search;

[0057] (3) If no valid SSA is found after tracing back upstream to the end of the track, mark the current track segment as having no valid SSA upstream or downstream and stop the search.

[0058] Step B: During the backtracking process upstream, the DFS algorithm is also used. If a switch is encountered, the switch location branch is traversed first until the end of the track is found, at which point the search for that branch stops. Then, following the last-in-first-out (LIFO) order of the stack, the reverse branches of the switches are popped out of the stack and searched accordingly. If an extreme point is encountered during the search, the search direction is reversed to continue.

[0059] Step C: If the convergence node encountered in step A(2) has a marker indicating that there is no valid SSA downstream on the track segment of both the positioning branch and the reverse branch, then merge these two branches and continue backtracking upstream from the convergence node until the stop search condition in step A is encountered.

[0060] Since there are multiple starting track ends in the electronic map data that meet the search start conditions of Step 1, when the DFS algorithm is pruned and optimized using the backtracking algorithm, a mark can be made for the path that has been searched once. In the subsequent search of multiple paths, if it is determined that there is no valid SSA downstream of the current track segment, the search will stop, which can avoid the problem of repeated searching of invalid paths.

[0061] The optimization method based on depth-first traversal of track segments mentioned above can only prune invalid paths downstream in the search direction. When there are few invalid paths downstream, the pruning effect of the backtracking algorithm will be insignificant. However, by employing memoized search, which marks already processed track segments, the rate of repeated searches can be reduced, thereby improving the running speed of the DFS algorithm.

[0062] For the track segments traversed in Step 2 of the DFS algorithm, a priori condition needs to be added to determine whether the Adjacent_SSA has already been generated. The determination logic is as follows:

[0063] 1) If the track segment has not been processed to generate Adjacent_SSA, mark it as already processed and continue searching downstream;

[0064] 2) If the track segment has already been processed to generate Adjacent_SSA, and the current SSA_Begin is empty, it means that the current search path from the end of the track to the current track segment is an invalid path, and all downstream branches from the current track segment have been traversed. Therefore, the search is stopped to avoid repeated searches.

[0065] 3) If the track segment has already been processed to generate Adjacent_SSA, but the current SSA_Begin is not empty, continue searching downstream. If SSA_next is found, after generating Adjacent_SSA, search for the element with SSA_next as SSA_Begin from the Adjacent_SSA list. If found, stop searching, indicating that the downstream path has been traversed.

[0066] In one embodiment of the present invention, the track section connection is as follows: Figure 5 As shown, to generate the Adjacent_SSA list elements, follow the instructions. Figure 1 The specific steps of this invention, the traversal process is as follows:

[0067] Generate a list of Adjacent_SSAs for the Up direction:

[0068] Route 1: Obtain the starting point for the path search in the Up direction. Given track segments B1 and B10, select B1 to start the search downstream in the Up direction. The search path is B1, B2, B3, B4, B5, B6, B7, B8, B9, generating Adjacent_SSAs: (B2, B4), (B4, B6), (B6, B8). When encountering the end of track B9, the search stops and begins backtracking upstream. If a valid SSA is found at B8, a pruning mark is placed on B9. Then, backtracking to B22, the downstream search path is B22, B23, B16, B17, B18, B19. When encountering the end of track B19, backtracking upstream, a convergence node is encountered at B18, and a pruning mark is placed on B18. Next, the search proceeds downstream from B26, following the path B26-B27. Upon encountering the end of the track at B27, the search backtracks upstream. A convergence node is encountered at B26, and a pruning marker is placed on B26. Since a pruning marker is also found at B18, the search continues upstream, encountering a convergence node at B17, where a pruning marker is placed. Then, the search proceeds downstream from B24, following the path B24-B25. Upon encountering the end of the track at B25, the search backtracks upstream, encountering a convergence node at B24, where a pruning marker is placed. Since a pruning marker is also found at B17, the search continues upstream, placing pruning markers at B22 and B15 respectively. Then, backtracking to B20, the downstream search path is B20, B21, B14, generating Adjacent_SSA: (B4, B14). The search stops at B15 when a pruning marker is encountered.

[0069] Route2: Start searching downstream from B10. The search path is B10, B11, B12, B13, B14, generating Adjacent_SSA: (B11, B14). The search stops when the pruning marker is encountered at B15.

[0070] Generate a list of Adjacent_SSAs in the Down direction:

[0071] Route3: Get the starting point for the path search in the Down direction, which is B9, B27, B19, B25. Select B9 to start the search downstream in the Down direction. The search path is B9, B8, B7, B6, B5, B4, B3, B2, B1, generating Adjacent_SSA: (B8, B6), (B6, B4), (B4, B2).

[0072] Route 4: Starting from B27, the search proceeds downstream in the Down direction. The search path is B27, B26, B17, B16, B15, B14, B13, B12, B11, B10, generating an Adjacent_SSA: (B14, B11). Then, it backtracks to B21 and continues searching downstream in the Down direction, with the search path being B21, B20, B4. Although a processed marker is encountered at B4, the current SSA_Begin is B14, which is not empty, generating an Adjacent_SSA: (B14, B4). Using B4 as the new SSA_Begin, it finds that an object (B4, B2) with B4 as the SSA_Begin has already been generated in the Adjacent_SSA list, so the search stops. Next, it backtracks to B23 and continues searching downstream in the Down direction, with the search path being B23, B22. A processed marker is encountered at B6, and there is no SSA_Begin upstream, so the search stops.

[0073] Route 5: Start searching downstream from B19 in the Down direction. The search path is B19, B18. If a processed marker is encountered at B17 and there is no SSA_Begin upstream, the search stops.

[0074] Route 6: Select B25 to start searching downstream in the Down direction. The search path is B25, B24. If a processed marker is encountered at B16 and there is no SSA_Begin upstream, the search stops.

[0075] Figure 5 The SSA in the middle is an SSA that meets the conditions in both the up and down directions. However, in the actual electronic map data of the entire line, the number of SSAs that meet the conditions in the up and down directions is not symmetrical. According to the scenario of vehicles running up and down, the track segments need to be traversed separately for the up and down directions to generate the corresponding Adjacent_SSA objects. Based on the depth-first traversal algorithm, the backtracking algorithm and the memory search algorithm can effectively reduce the redundancy of track segment traversal, thereby effectively improving the running efficiency of the software.

[0076] The above is an introduction to the method embodiments. The following embodiments using electronic devices and storage media will further illustrate the solution of the present invention.

[0077] This invention also provides an electronic device including a central processing unit (CPU), which can perform various appropriate actions and processes according to computer program instructions stored in a read-only memory (ROM) or loaded from a storage unit into a random access memory (RAM). The RAM may also store various programs and data required for device operation. The CPU, ROM, and RAM are interconnected via a bus. Input / output (I / O) interfaces are also connected to the bus.

[0078] Multiple components in the device are connected to the I / O interface, including: input units such as keyboards and mice; output units such as various types of displays and speakers; storage units such as disks and optical discs; and communication units such as network interface cards (NICs), modems, and wireless transceivers. The communication unit allows the device to exchange information / data with other devices through computer networks such as the Internet and / or various telecommunications networks.

[0079] The processing unit performs the various methods and processes described above, such as the methods of the present invention. For example, in some embodiments, the methods of the present invention may be implemented as computer software programs tangibly contained in a machine-readable medium, such as a storage unit. In some embodiments, part or all of the computer program may be loaded and / or installed on the device via ROM and / or a communication unit. When the computer program is loaded into RAM and executed by the CPU, one or more steps of the methods of the present invention described above may be performed. Alternatively, in other embodiments, the CPU may be configured to execute the methods of the present invention by any other suitable means (e.g., by means of firmware).

[0080] The functions described above in this document can be performed, at least in part, by one or more hardware logic components. For example, exemplary types of hardware logic components that can be used, without limitation, include: Field Programmable Gate Arrays (FPGAs), Application-Specific Integrated Circuits (ASICs), Application Standard Products (ASSPs), System-on-Chip (SoCs), Complex Programmable Logic Devices (CPLDs), and so on.

[0081] The program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This program code can be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0082] In the context of this invention, a machine-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. Machine-readable media can include, but are not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fibers, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0083] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for traversing track segments based on a depth-first search algorithm, characterized in that, This method uses backtracking to prune invalid paths and memory to mark already processed track segments. The method specifically includes the following steps: Step S1: Parameter initialization. Obtain all path search starting points in the electronic map and use the depth-first search algorithm to search downstream from the path starting point. In step S2, if a pruning marker is encountered, the search is stopped and the search is backtracked to other branches that have not been searched to continue the depth-first traversal search. Step S3: If the searched track segment has been processed and meets the condition that the downstream search no longer needs to continue, then stop the search; if the searched track segment has not been processed, then mark it as processed and continue searching downstream. Step S4: If the end of the track is found, stop the search and backtrack upstream from the end of the track to prune invalid paths and mark the pruning points on the corresponding track segments. Step S5: If all the starting points of the path search in step S1 have been traversed and searched, then the search is complete. In step S3, marking whether the track segment has been processed specifically involves: The optimization method of memory search is adopted. If it has been processed and the downstream does not need to be searched, the search is ended early. Any processed track segment must be marked as processed. In step S4, the backtracking process, starting from the end of the track and moving upstream, is used to prune invalid paths. Specifically, this involves: If the target solution is encountered during the backtracking process, a pruning mark is placed on the first track segment downstream of the target solution; If a convergence node is encountered during the backtracking process, a pruning mark is placed on the track segment where the convergence node is located; and when both the positioning branch and the reverse branch of the convergence node have been marked with pruning marks on their track segments, the two branches are merged and the backtracking continues upstream from the convergence node. If the end of a track is encountered during the backtracking process, a pruning mark is placed on that track segment.

2. The method for traversing track segments based on a depth-first search algorithm according to claim 1, characterized in that, The specific starting point for the path search in step S1 is: If there are no other connected track segments upstream of this track segment, then this track segment will be used as the starting point to search downstream.

3. The method for traversing track segments based on a depth-first search algorithm according to claim 1, characterized in that, The specific steps in step S1, which involve using a depth-first search algorithm to search downstream from the starting point of the path, are as follows: First, start the search from the starting point and search in a single direction. When a turnout is encountered, prioritize searching to locate the direction. Continue searching until the end of the line. Then, according to the stack first-in-last-out principle, retreat to the track section where the turnout is reversed and continue searching downstream.

4. The method for traversing track segments based on a depth-first search algorithm according to claim 1, characterized in that, The pruning mark in step S2 is specifically a mark indicating whether the downstream of the track segment needs to be searched. If a pruning mark is found, the search stops and the search returns to other branches that have not been searched.

5. The method for traversing track segments based on a depth-first search algorithm according to claim 1, characterized in that, In step S3, if the condition that no downstream search is required is met, the judgment is made according to the algorithm for generating the target solution.

6. The method for traversing track segments based on a depth-first search algorithm according to claim 1, characterized in that, In step S4, during the backtracking process from the end of the track upstream, the DFS algorithm is used. If a turnout is encountered, the turnout location branch is traversed first until the end of the track is reached, at which point the search for that branch is stopped. Then, the reverse branches of the turnout are popped out of the stack in the order of last-in-first-out (LIFO) and searched accordingly. If an extreme point is encountered during the search, the search is reversed and the search continues.

7. The method for traversing track segments based on a depth-first search algorithm according to claim 1, characterized in that, In step S5, if the path search starting point in step S1 has been traversed and searched, then the search is complete; otherwise, continue searching downstream from the search starting point, performing a depth-first traversal according to the situations in steps S2, S3, and S4.

8. An electronic device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the program, it implements the method as described in any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the program is executed by the processor, it implements the method as described in any one of claims 1 to 7.

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