## 2 Literature Review
### The Application of Digital Information Technology in the Conservation of Cultural Heritage  
In recent years, digital information technology has been widely discussed and used in the field of conservation and the reproduction of cultural heritage of historical buildings. Browsing buildings and executing spatial queries through a virtual 3D environment can help professionals find all the information needed for the conservation and maintenance of architectural heritage, and develop appropriate strategies [14]. The 3D visualization of historical scene information modeling becomes key to communication [5; 15]. As the simple 3D geometric model lacks information about a building and its components, research has begun to apply building information modeling (BIM) technology in the construction process of cultural heritage conservation.  
The historical parameter library, which is a parametric modeling method that uses historical documents and actual survey results as data, is a new area for BIM. Historic building information modeling (HBIM) provides a method [16] for the parametric modeling of historic buildings, including laser scanning and photogrammetry data. The HBIM process starts from point clouds, photo modeling, and measurement data collection, which is a reverse engineering process [1; 17], provides a variety of workflows for historic buildings, and digitizes buildings and documents. Existing historic buildings require very complex workflows, and often involve a hybrid approach for different data, such as CAD drawing files, point clouds, photo modeling, and the collection of measurement data. The parametric model, which is a combination of information modeling technology and historical data construction, is generated by HBIM and is especially suitable for preservation. Moreover, it allows research to be conducted on the technical construction system of historical buildings [18].  
However, in terms of interface use, the current BIM software is not mature enough for the conservation of historical buildings and cultural heritage, and most research on the information model only focused on a single building, which cannot express the relationship between the historical building and an old city block, and thus, is not conducive to the conservation and restoration of historical buildings and cultural heritage. Furthermore, the focus on historical building models must be extended to include whole geographic information blocks [19; 20], meaning the geographical information of nearby old city blocks should be added to conduct comprehensive data analysis among such objects [21]. 3D-GIS digital technology plays a very important role [4], as its application in 3D model visualization can accurately record and truly present historical scenes, and provide users with sufficient details of urban blocks and building information for reconstruction.  
At present, BIM and 3D-GIS are mostly defined as 3D information tools, which can generate 3D visual models of cultural heritage sites. Through a three-stage technique of information integration, conceptual modeling, data structuring, and data presentation, researchers are able to present shared data between historic blocks and buildings in 3D digital form. Information integration technology is not only an advantage of model visualization, it can also represent the unique geometric form of historical buildings, cultural semantics, and historical information, and their value [14; 20; 22].