## 2 Methods
### Visualization of PV Output by Integrating a GIS and a BIM Environment  
Visualizing the candidate sites for PV plants in a BIM environment can support the communication and management of energy infrastructure systems. In this visualization stage, the proposed sites and PV array systems are modeled in a BIM platform by integrating the GIS into the BIM environment through two processes: (1) data transformation and (2) model visualization.  
In the data-transformation process (Figure 5), to integrate the GIS and BIM environment, topographic data (i.e., terrain maps), spatial data (i.e., highway layer), and the result of the PV power output are converted in different manners. The topographic data, represented by a two-dimensional (2D) DEM map on the GIS, are converted into a toposurface map in the BIM, where points containing (x, y, z) coordinates are placed. Specifically, each elevation value included in each grid of DEM map (raster image) is extracted to contour map with an interval of 30 m, and its contour map is converted into a point layer including geometry (x, y) positions from coordinate and its layer is saved as (x, y, z) format in CSV (Comma-separated values) file format. Then, the CSV data, containing elevation data from a certain location, are transformed into a toposurface in the BIM. Furthermore, vector format-based spatial data (highway network) are converted into a DWG (from drawing) file using the GIS function (Export to CAD). Based on [PERSON] et al., 2019 [PERSON] et al. (2019), it was assumed that there are no GIS data loss in the data conversion of this study.  
However, the converted highway network data do not contain z values (i.e., elevation), indicating that the highway data are represented by the subregion, which overlays the x-y, based on the highway network layer. In addition, the raster image-based result of the PV power output is converted into a point layer and then saved in CSV file format, including (x, y, z) coordinates and PV power-output values. This CSV file is imported into the BIM using Dynamo, an open-source visual programming language for Revit, to address the limitations of parametric modeling and data-management processes ([PERSON] et al., 2019). In short, the (x, y, z) coordinates are transformed into solar-panel families in the BIM environment.  
In the final step, the plan view of the PV plants in a candidate region near the highway network is represented by placing a solar panel family on the same scale (i.e., 1/5000) as the spatial data to the location points in the BIM environment. In particular, to pinpoint the solar-panel families in the 3D environments (i.e., toposurface), which are the same as the position of the expected solar PV power generation computed through the spatial analysis (Section 2.2) and the evaluation of the PV power output (Section 2.3) on the GIS, the elevation is set differently, depending on the dimensions of the spatial data (e.g., solar PV power-output data, highway network data) in the BIM environment.  
Figure 5: Conceptual illustration of data transformation for the integration of BIM and GIS.  
The highway network data are represented in GIS in 2D format and cannot be placed on the 3D toposurfaces. Therefore, as shown in Figure 6, the highway data are imported 1000 m higher than the toposurface to prevent them from being obscured by the toposurface. Then, its data are converted into a subregion shape, based on 0 m in the building elevation (level). Meanwhile, the solar PV power output data, including 3D coordinates (x, y, z), are placed on a toposurface using the Dynamo function with the solar panel family. For example, because point data (i.e., PV power output) cannot be imported directly into the BIM, the Point.ByCoordinates function from Dynamo is used to position the PV power output as solar-panel families on the toposurface.