Validating the Sun System in Blender for Recreating Shadows

Shadow positions can be useful in determining the time of day that a photograph was taken and determining the position, size, and orientation of an object casting a shadow in a scene. Astronomical equations can predict the location of the sun relative to the earth, and therefore the position of shadows cast by objects, based on the location’s latitude and longitude as well as the date and time. 3D computer software have begun to include these calculations as a part of their built-in sun systems. In this paper, the authors examine the sun system in the 3D modeling software Blender to determine its accuracy for use in accident reconstruction. A parking lot was scanned using Faro LiDAR scanner to create a point cloud of the environment. A camera was then set up on a tripod at the environment and photographs were taken at various times throughout the day from the same location in the environment. This environment was then 3D modeled in Blender based on the point cloud, and the sun system in Blender was set up using the date and time of the photographs. The photographs from the environment were then undistorted and aligned to the 3D environment using photogrammetry techniques, and images were rendered in the same positions to compare the shadows in Blender’s Cycles render engine to the photographs. Through this process, the authors determined that Blender’s sun system recreates the sun position adequately, and can be used to accurately determine the location and dimensions of shadows cast by objects of known dimensions and location.