## 2 Materials and Methods
### GIS Entity Data Collecting and Storage  
Although the oblique photogrammetric 3D modeling technique reconstructs a 3D scene, the model comprises a point cloud and triangulated irregular network (TIN) and is represented by the \"skin\", which means that all objects (GIS entities) are physically grouped together. This avoids being clicked, queried, and implemented to other basic GIS functions, inhibiting its capacity to meet sophisticated GIS needs. Therefore, generating monomer models from TIN-based 3D models is mandatory. Some solutions have used the real 3D model to produce monomer 3D models, mainly including slicing, ID, and dynamic rendering-based methods. The slicing-based method directly cuts the target objects on the TIN mesh surface of the 3D real model to derive the corresponding individual models. However, this operation destroyed the Level of Detail (LOD) and model texture, leading to a sharp decline in 3D viewing efficiency and visual quality when we rendered them in the Cesium virtual globe. The ID-based method realized monomer modeling by searching the TIN points belonging to the same object that must be isolated and then assigning the same ID value for these searched TIN points. This method's difficulty is determining the TIN points of the same object. Unlike the above two methods, the third method adopted in our study manually collects the feature points of an object on the bottom profile. After that, the Cesium-based rendering mode of \"fitting to ground\" depicts the outer geometry of an object in the form of a \"skin\". This method does not destroy the structure of the raw data and completely represents an object, with the monomerized results typically suitable for GIS operations and applications. Figure 9 depicts the monomerized results of the building using the above three methods. After completing an object's monomer operation, the attribute information needed by the GIS application should be linked to it. As mentioned above, the dynamic rendering-based monomer method should be conducted on the Cesium Earth. Therefore, to effectively perform monomerizing and establish the corresponding GIS databases, we developed a graphics interactive platform in the Cesium environment by coupling the two sequential steps initiated from the developed functional module of \"data management\" (see Section 3.2 for details). Figure 10 presents the process of GIS entity data collection and storage. We take the building rendered pink in Figure 10 as an example. After receiving the real-scene 3D model data in 3D Tiles format from the server, an editing mechanism enables users to add or edit this building in the scene. Based on the pop-up interface, we interactively measure the geometry data depicted by the building corners on the bottom profile and store them as geographic coordinates in the format of longitude and latitude. At the same time, attribute information can be added and linked to this building in the pop-up interface. After that, a data record related to this building was stored in a predefined MySQL database for a house entity and can be reloaded later, if necessary. Figure 10 presents four data records corresponding to four buildings. Apart from mining working-face data, other GIS entity data collection methods (Table 3) can used, like for the building according to the rules we set. Regarding the mining working-face data corresponding to the polygon entity, its geometry and property data can be acquired from the planned CAD drawings or thematic maps. Such data in China are generally represented in a Gauss planar coordinate system. They should be converted to geographic coordinates and transferred to JSON format to make the data more readable and writable in a web-friendly format. The collected data associated with attribute information of mining-work face are stored in its GIS database. On the other hand, based on the established GIS database, the query function acts similarly to a bidirectional interaction mechanism initiated by clicking an object or a record in the GIS data table.