# Web3 DGIS-Based System for Reservoir Landslide Monitoring and Early Warning
## 4 Key Technologies
### Multi-Data Organization and Management
#### 4.1.2 Three-Dimensional Scene Data Organization  
In order to establish an accurate image of the target area, researchers need to integrate remote image data with the digital elevation model, overlapped with multiple geological factors, so as to allow functions including browse, cruise, consultancy, measurement, and analysis in a three-dimensional space. The main data for three-dimensional scene construction are from highly accurate digital evaluation models and high-resolution digital orthophoto maps, whose data are normally restored in the form of a lattice. As a direct three-dimensional display can severely affect system effectiveness and due to the difficulties of achieving real time-mapping of the three-dimensional scene, this study combined the tile pyramid model method with a linear quad-tree index in order to preprocess and reorganize the data needed for the scene [33].  
The pyramid model contains multiple resolution levels (Figure 5). When constructing the pyramid, the original lattice data (e.g., the digital evaluation model or remote image) is first set to the bottom (No. 0 level) of the pyramid tile matrix. Based on the No. 0 level, every 2 \(\times\) 2 lattice unit combines together into one unit to form the 1 level lattice matrix. This process is then repeated to form the whole tile pyramid [34].  
Figure 4: Entity Relationship Diagram of real-time monitoring data model.  
Figure 5: Image tile pyramid model.  
A quad-tree is a tree structure with up to 4 branches in each non-leaf node [33]. It is also a hierarchical data structure, featuring spatial interconnection rescission. The quad-tree structure offers convenience for the index and management of tile data. Based on tile pyramid, the construction of quad-tree index can be divided into three steps: logical partitioning, node coding, and physical partitioning. After partitioning, a topological relationship between tiles is built, which includes two aspects: a neighboring link of the same level and higher, and lower relationships (e.g., that of parents and their children).  
The above method can, to a great extent, satisfy the need to visualize a three-dimensional scene in a large area; therefore, it can greatly improve the display effectiveness of the system. This is primarily because cutting out topographical data from outside of the view and using a fast tile search method based on resolution rate greatly reduces the amount of data described in a scene. While mapping the scene, for the specific display proportion, data from the digital elevation model and the image texture of a specific pyramid level (the closest to the display resolution rate) are directly used in the rapid representation of the three-dimensional surface.  
After considering the Browser/Server structure of the system, users can set a client-oriented browser and a quick three-dimensional display of related data. To ensure a fluent display of the three-dimensional scene, this study adopted several measures, including a seamless network and the effective transmission of three-dimensional data. Once the initial image is accepted by the user in a low-resolution state, the client displays the three-dimensional data, without waiting for the full transmission of data. Using a distribution system and load balance technology, different servers in different areas can share the burden of three-dimensional data collection; thus, automatically distributing load among all applicable servers.