A New 3‐<scp>D</scp> Solar Radiation Model for 3‐<scp>D</scp> City Models

Abstract Estimates of solar radiation distribution in urban areas are often limited by the complexity of urban environments. These limitations arise from spatial structures such as buildings and trees that affect spatial and temporal distributions of solar fluxes over urban surfaces. The traditional solar radiation models implemented in GIS can address this problem only partially. They can be adequately used only for 2‐ D surfaces such as terrain and rooftops. However, vertical surfaces, such as facades, require a 3‐ D approach. This study presents a new 3‐ D solar radiation model for urban areas represented by 3‐ D city models. The v.sun module implemented in GRASS GIS is based on the existing solar radiation methodology used in the topographic r.sun model with a new capability to process 3‐ D vector data representing complex urban environments. The calculation procedure is based on the combined vector‐voxel approach segmenting the 3‐ D vector objects to smaller polygon elements according to a voxel data structure of the volume region. The shadowing effects of surrounding objects are considered using a unique shadowing algorithm. The proposed model has been applied to the sample urban area with results showing strong spatial and temporal variations of solar radiation flows over complex urban surfaces.