Abstract : The urban rail transit basic geographic information system is a large-scale information management system that uses the theories and methods of geography, geological engineering, computer graphics, computational mathematics and other disciplines, based on geographic information system technology, combined with database processing, programming technology in ArcGIS and three-dimensional image processing technology to comprehensively manage and analyze the basic data of urban rail transit. Based on the user needs of the urban rail transit basic geographic information system, the functional characteristics of the urban rail transit basic geographic information system are described; the three-dimensional spatial visualization method of rail transit basic data based on the geographic information system platform is discussed. Keywords: urban rail transit, geographic information system, design 0 Introduction Since China began to build subways in 1965, the scale of urban rail transit construction has continued to expand[1]. Although a massive number of engineering geological surveys and rail projects have been completed over the past 40 years, a significant portion of the urban rail transit basic geographic information, including planning data and basic geological survey data generated in these projects, remains in a state of fragmented use, fragmented storage, and even widespread abandonment. Furthermore, the current storage and management of urban rail transit basic geographic information still relies primarily on traditional methods such as text, drawings, and charts, making retrieval inconvenient, especially when processing large amounts of engineering data. Therefore, a modern information management system is essential, and the development of Geographic Information System (GIS) technology provides a suitable and practical tool for this purpose. GIS is a geographical research technology that began to develop rapidly in the 1960s, a product of the intersection of multiple disciplines. In recent years, GIS has experienced unprecedented rapid development globally, becoming a high-tech solution for modern scientific management. It is widely used in urban planning, urban underground pipeline management, urban transportation, and social services. GIS possesses the capabilities to store massive amounts of data, perform complex logical operations and data mining, and is also an effective tool for spatial graphic display and spatial information query and analysis. By utilizing the data input, storage, retrieval, display, and comprehensive analysis functions of GIS [2-3], the spatial information of urban rail transit basic data is combined with its related attribute information, enabling the retrieval, statistics, analysis, modification, and printing of urban rail transit basic geographic information, providing a fast and accurate modern management method for urban rail transit basic geographic information. In addition, there is a large amount of engineering geological data and underground pipeline data in urban rail transit basic data. Traditional data management makes it difficult to visualize different types of data in three dimensions, and it is also impossible to analyze and process the data. The three-dimensional visualization function of geographic information system is to establish a feature mathematical model with an appropriate data structure and use computer graphics technology to represent the mathematical description in the form of 3D images, thus realizing the visualization of urban rail transit basic data management. 1 Analysis and Design of Urban Rail Transit Basic GIS 1.1 Overall Structure The system utilizes the powerful map operation functions of ArcGIS to realize the visualization management and analysis of basic geographic data such as strata, boreholes, monitoring, structures, and pipelines involved in urban rail transit. The system consists of four parts: hardware, GIS software and system software, database, and interface. Its overall structure is shown in Figure 1. 1.2 Module Design The system needs to manage a large amount of spatial and attribute data along the rail transit lines, and also realize the visualization analysis of geological data, structure data, and pipeline data. Based on general software design principles, the system adopts a modular design. It is divided into three subsystems: thematic information management, basic information management, and system maintenance, consisting of a total of eight modules, as shown in Figure 2. 1.3 System Functions The system requires establishing relationships between isolated and scattered urban rail transit basic data using geospatial data as a link, and on this basis, developing a GIS-based urban rail transit basic geographic information system. This will integrate various borehole data, basic data of structures around the track, ground topography data, and underground pipeline data into an organic whole; perform retrieval, query, and analysis of urban rail transit basic information; enable three-dimensional display of geological information; and initially form a scalable urban rail transit basic information database. The main functions of the system are as follows: 1) Map operation functions. This includes map zooming, panning, and movement; layered display of various graphic elements; and arbitrary range printing of graphics. 2) Attribute data entry and editing. A dedicated attribute database table is established for the attributes of all graphics. Data entry, editing, and modification are completed through the data maintenance submodule. The main attribute data operation objects include rail transit overview, basic borehole information, rail project construction information, geological stratification information, information on various underground pipelines, information on surface buildings, foundation information of structures, monitoring data, etc. 3) Graphic Input and Editing. System data includes two types: spatial data and spatial attribute data. Spatial data refers to two-dimensional planar data, mainly including point, line, and area data such as rail transit and stations, topography, geological structures, buildings, boreholes, pipelines, and foundations of structures. This data is organized in layers and represented on the planar map in the form of vector maps. The system can edit spatial data through the data maintenance submodule, i.e., add and delete points, lines, and areas. 4) Information Retrieval and Query Functions. The system can simultaneously perform convenient, flexible, and accurate queries and positioning of spatial and attribute data. It realizes bidirectional joint query and analysis of spatial graphic data and attribute data, allowing users to query required attribute information from graphic information and query graphic information based on various attribute information conditions. The system is designed with various query methods, including click, condition, and logical queries, and features multiple query and retrieval functions such as spatial location, attribute, and range. 5) Information visualization function. The system can display information from the database in the form of text, maps, and images, and provides users with functions such as layered display and selection of various elements. The system uses points and lines as basic forms, borehole data as the foundation, and selects appropriate interpolation methods to construct stratigraphic information from scattered and local two-dimensional geological borehole data and display it in three-dimensional space; it also reproduces the underground spatial morphology and combination relationships, reconstructs a three-dimensional model, and vividly represents it with three-dimensional graphics, thereby realizing the expression, analysis, and three-dimensional visualization of the complex underground spatial structure and relationships. Through three-dimensional track visualization, the general situation of the track and its surrounding areas can be reflected intuitively and vividly. 6) Spatial analysis function. Powerful system analysis function is one of the advantages of GIS. Based on existing spatial data, using buffer analysis, network analysis, overlay analysis, and data mining techniques, it supports decision-making research on complex spatial problems and simulates and predicts changing trends. For example: A buffer zone of arbitrary length can be established centered on the track line to analyze the distribution of various pipelines within the buffer zone, display the pipeline closest to the track within a certain range, or perform collision checks; a large amount of long-term track monitoring data can also be comprehensively analyzed to establish a regression analysis model to predict track settlement changes. 7) Digital image overlay. After registering ground image data, it can be overlaid on vector maps to enhance ground visualization. Ground feature analysis can also be performed on this basis. 8) User permission settings. Two types of users can be set as needed: administrators and clients. Users must use an account and password to enter the system. Administrators have full permissions, including system backup, data entry, modification, query, deletion, and printing, as well as adding and deleting clients; clients have basic permissions such as data query, statistics, and printing. There can be one or multiple clients. 2 Implementation of Urban Rail Transit Basic GIS 2.1 Database Processing Based on the system's basic functions and data encoding, a database management system based on SQL Server is established. The data model objects in the database can be divided into the following categories: track engineering information table, borehole basic information table, profile stratigraphic information table, stratigraphic basic information table, borehole stratum information table, structure foundation basic information table, structure foundation stratum table, pipeline basic information table, pipeline stratum information table, etc. This is used to establish a graphic attribute database and to associate graphic attribute values ​​with index fields. The database index fields are located by the graphic attribute values, which are then used to call other related field content. 2.2 GIS Secondary Development Technology The system uses ArcGIS as the secondary development platform, calling some excellent functional modules of ArcGIS and modifying and improving them, specifically in the following ways: 1) Graphic data attribute editing. Graphic attributes and their structures are defined according to relevant industry standards, and a connection with the database is established to improve the software's professional level. 2) Library file expansion. Legends and various professional symbols are defined according to industry standards, expanding ArcGIS's legend library and graphic library for display and retrieval. 3) Thematic analysis of basic data of track-line structures and pipeline data is conducted based on buffer analysis and overlay analysis. 2.3 Integrated Display of Urban Rail Transit Basic Data 1) Using remote sensing image registration, building mapping, and 3D modeling technology, a three-dimensional display of ground landscape and buildings is achieved. 2) Based on precise coordinate positioning, the positional relationship between basic data of structures, pipelines, and track data is determined, enabling the display of underground track basic data. Simultaneously, with the support of ArcGIS functional modules, system query functions can be developed to enable the query and analysis of basic data of various pipelines and structures within the track area. 3) Based on the multi-layer DEM/TIN hybrid algorithm and using borehole data as a foundation, the geological data through which the track passes is visualized. First, the comprehensive stratigraphic sequence of the area along the track is determined; second, the construction of individual strata is formed layer by layer, with each stratum represented by two geological layers above and below; finally, within the area, color and texture are filled between the two layers [4-5]. 3 Applications 1) Graphic display function. Figure 3 shows the main interface of this system, displaying the Shanghai Rail Transit planning map. 2) Track, pipeline, and other basic data query. Clicking on graphic elements displays graphic attribute information; query conditions can also be entered to search database information. As shown in Figure 4. 3) 3D display of ground buildings. After registration, the remote sensing images are overlaid on the 3D environment for display, as shown in Figure 5. 4) 3D display interface of underground foundation data, as shown in Figure 6. 4. Conclusion 1) The urban rail transit basic geographic information system is characterized by openness, universality, ease of operation, ease of maintenance, and ease of expansion. It is a multi-functional information management system that integrates practicality and comprehensiveness. 2) The application of the urban rail transit basic geographic information system can integrate urban rail transit basic data from various sources, thereby achieving data sharing. 3) The establishment and analysis functions of the three-dimensional data model realize the visualization of various basic geographic information along the rail line, providing an intuitive way to browse and query urban rail transit basic geographic information, and promoting the informatization of urban rail transit basic data management. 4) The preliminary realization of the correlation display and analysis functions between above-ground buildings and underground elements has good universality and can be further developed and applied. 5) On the basis of fully realizing the inherent functions of the system, data mining and the development and integration of new functions can be carried out in depth, which will greatly improve the efficiency and quality of urban rail transit basic information management, and make great strides towards scientific, digital, and visualized urban rail transit basic information management. 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