## 5 Camera Placement based on HybVOR Approach
### Hybrid Assessing of the Camera Network Coverage
#### 5.3.2 3D Vector-Based Analysis of Visibility  
The benefit of using a 3D vector model is to perform visibility analysis on elements that cannot be assessed based on a raster DSM. Indeed, a raster DSM allows only the Viewsheed calculation of objects and features that are on the surface. Hence, roofs are the only components of buildings that may be present in a raster DSM. Other vertical components of buildings such as facades, doors, windows cannot be modeled in a raster DSM. For this reason, it is necessary to complete the coverage assessment of the camera network with a 3D vector-based analysis of visibility. This method of visibility analysis consists of constructing lines of sight among each camera and objects of interest that will be monitored from this location (Figure 2). To do so, it is necessary to establish a many-to-many relationship between the class \"Camera\" and the class that represents the objects to be monitored. The class \"Camera\" contains very important information about the properties and the 3D position of cameras, which are necessary to configure the spatial layout of the deployed network. In our case, the class \"Entrance\" represents the main entrances of buildings (doors and windows). This many-to-many relationship means that a camera may monitor zero, one or many entrances, and an entrance has to be monitored by one or many cameras (Figure 14). In the absence of such a relation, the software will create a line of sight between each camera and all vertices in the 3D model, which will lead to an excessive amount of time and provides results which are difficult to interpret. Figure 14 shows the UML notation of the many-to-many relationship between the classes \"Camera\" and \"Entrance\".  
Figure 13: The attribute table of the class “Camera”.  
The constructed lines of sight represent straight lines that link between the observation point (camera) and the target feature. It is possible to construct several lines of sight between a camera and a target feature if this latter is either a line or polygon feature by applying a sampling distance.  
The 3D Vector-based analysis of visibility consists of combining 3D models that represent objects in the monitored environment with the constructed lines of sight. The aim is to check whether these objects intersect the lines of sight between the camera and the target. Three cases may occur (Figure 15):  
1. If there are one or many objects in the environment that intersect all lines of sight between the camera and the target, then this target is completely invisible from the camera.
2. If there are one or many objects in the environment that intersect some lines of sight (not all lines of sight) between the camera and the target, then this target is partially visible from the camera.
3. If there is no object that intersects lines of sight between the camera and the target, then this target is fully visible form the camera.  
Figure 14: Unified Modeling Language notation of the many-to-many relationship between the classes “Camera” and “Entrance”.  
Figure 15: _Cont._  
Figure 16 summarizes the main steps in the implementation process of the HybVOR approach for deploying surveillance camera network.  
Figure 16: The main phases of implementing the Hybrid Voronoi (HybVOR) approach.  
Figure 15: Three possible cases that may result from 3D Vector-based analysis of visibility; Case 1: The target is partially visible, Case 2: The target is completely not visible, and Case 3: The target is fully visible.  
In Section 6, the results of implementing the HybVOR approach are presented. The aim is to find the optimal placement of camera network for monitoring an area of interest in Jeddah Seaport.