## 3 Results
### Practical Application and Spatial Accuracy Evaluation of the Prototype System
Selecting a deformation type: By pushing the \"MIDA\" menu, a pop-up sub-interface named \"MIDA\" would be displayed in the central part of the main interface. In this subwindow, we should first select a deformation type from the combo list, which consists of different deformation types, as mentioned in Section 2.7. 2. Computing the deformation contours: Once a deformation type is confirmed, the system can post a PIM execution HTTP request to the server. When the server receives this client-side request, the MIDA engine is triggered to perform surface deformation calculations. After that, the corresponding deformation isolines will be computed on the serving side and returned to the client side to be rendered and visualized on the background layers. These deformation isolines represent different impact areas in the shape of 2D polygon contours. 3. Selecting the interested GIS entity data and performing overlapping analysis: The GIS vector data are organized with down-left data layer lists in the \"MIDA\" sub-interface according to entity types (i.e., point, line, and polygon), and for each entity type, it was also classified into several subtypes by a set of expandable nodes. We can choose the interested data type in this data layers list for GIS analysis. Subsequently, we can manually click and select a deformation isoline to trigger the GIS overlapping analysis model engine for performing deformation analysis, i.e., we used the selected 2D deformation contour and the interested data layers chosen above as a background polygon and target geometries, respectively, to perform an intersecting calculation for interested data layers. The computational results are pushed to the client-side application for visual rendering in real time. After this process, the analysis results will be produced and stored in the GIS database. At the same time, the selected interested data layers list will be updated and displayed in the down-right data grid table of the \"MIDA\" sub-interface. Take two deformation types of subsidence and horizontal movement as examples to illustrate the results of the MIDA presented in Figure 16, in which the deformation contours and the selected isolines used as background polygons for intersection are rendered with green and red colors, respectively. Note that for clarity, the sparse representative sample data of the above two types of deformation isolines were extracted and used for GIS analysis. Figure 16a,b illustrate the damage analysis results using subsidence isoline (w) with a value of 10 mm and horizontal movement along the strike direction (u90) with a value of \(-\)10 mm, respectively. After the MIDA, only the intersected results of different types of objects inside the impacted region are rendered and displayed, and one can also click to select an arbitrary object inside this region to retrieve its attribute information from the results database. Once an object with a certain entity type is chosen, it will be highlighted with red, and its corresponding attribute information panel instantly appears. Figure 16a,b illustrate this process for a road (red line) and farmland (red polygon region). We tested the spatial accuracy of the proposed 3D webGIS system with two types of validation data. The first type is the geo-referenced ground points with distinguished features such as road or house corners and GCPs; the other is the spatial overlapping results data. The 3D locations of the former were measured in the raw, realistic 3D model and represented in the SC system by CC Acute Viewer software (Version 10.20) [51]; these were used as the true values and denoted as \(X_{\text{rel}}\)\(Y_{\text{rel}}\), and \(H_{\text{rel}}\), respectively. Their corresponding coordinates measured in the web platform are denoted as \(X_{\text{web}}\),\(Y_{\text{web}}\) and \(H_{\text{web}}\), respectively. This type of validation data is mainly used to assess the absolute accuracy of the system.