# Online Street View-Based Approach for Sky View Factor Estimation: A Case Study of Nanjing, China
## 3 Results  
### System Setting  
BMapSVF stands out as an online GIS tool with a browser-based interface that enables graphical user interface interaction (see Figure 6). It seamlessly incorporates Baidu Map, a semantic segmentation model, the fisheye image projection method, and the SVF calculation method. All features have been incorporated into the toolbox situated in the upper right corner, with the icons inside it are in SVG format:  
* Switch cities: Clicking the city list button in the top left corner initiates the switch; the map is then loaded to the corresponding city location. * Address search box: Address or place identification is accomplished through an automatic search in the address box. Upon clicking, the location is automatically pinpointed on the corresponding map position. * Panorama control: Activation of the panorama control button involves clicking and placing it on the map; revealing the covered area in the form of a blue route. * Location control: The positioning control button, when clicked, retrieves current position information. Preferably, the browser location interface is utilized for obtaining location information. If unsuccessful, the user IP location is invoked, and the result at the city level is returned. * Map toggle: Changes in map type, such as common street views, satellite views, and hybrid views of satellite and road networks, are achieved through map toggling. * Distance measurement: Distance measurement on the 2D map facilitates the determination of distances between measured objects. Figure 5: Estimation of the \(SVF\) with ArcGIS built-in tools: (**a**) the skyline of the SVF observation point is generated through the 3D urban building model; and (**b**) the skyline graph of the observing point with the SVF value. * Coordinate position: WGS84 and BD09 coordinates are entered into the dialog box; If the input is WGS84 coordinates, conversion to BD09 coordinates for positioning is carried out, and if it is BD09 coordinates, direct positioning occurs. * Sample collection: Single point sampling is executed through left-clicking, while multiple points are obtained through a csv file. SVF values are automatically calculated and stored in MySQL. * SVF distribution: The drawing of SVF values in colored markers on the map. * Map legend: The generation of symbols and colors representing SVF values. * Export: The exportation of results from the selected zone to a designated folder, including results in the folder and Microsoft Excel, concludes the process. The BSV images in this study were obtained through the API of the Baidu Maps Open Platform, configuring parameters such as user access keys, field of view, image size, and latitude-longitude positions, as shown in Table 2. The maximum horizontal field of view is 360\({}^{\circ}\), and the maximum vertical field of view is 180\({}^{\circ}\). When the horizontal field of view is set to 360\({}^{\circ}\), the image obtained through the API represents the entire panoramic view [33]. The requested parameters for BSV images, including the developer API key, image size, longitude and latitude coordinates, and horizontal field of view, are instrumental in the acquisition process. Through the BSV panorama API, URL requests are initiated to Baidu Maps, initiating a search the BSV panoramas within a specified locale and obtaining metadata in return [26] (see Figure 7). Should multiple BSV panoramas be available, the API automatically furnishes information regarding the BSV panorama in closest proximity to the input search center, with a predetermined radius of 50 m. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters** & **Description** \\ \hline ak & API key \\ width & panorama width \\ height & panorama height \\ location & panorama location coordinates (longitude, latitude) \\ fov & horizontal direction range, range [10\({}^{\circ}\), 360\({}^{\circ}\)] \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Required parameters of URL. Figure 6: The user interface of BMapSVF.