Validation of the Cycles Engine for Creation of Physically Correct Lighting Models 2019-01-1004

Vision is the primary sense used to navigate through this world when driving, walking, biking, or performing most tasks. and thus visibility is a critical concern in the design of roadways, pathways, vehicles, buildings, etc. and the investigation of accidents. In order to assess visibility, the accident scene can be documented under similar conditions. Geometric and photometric measurements can be taken for later analysis. Calibrated photographs or video of a recreated scene can be captured to illustrate the visibility at a later time. This process can often require significant coordination of the physical features at the scene. It can be difficult to precisely control the motion and timing of moving features such as pedestrians and vehicles. The result is fixed in that you capture specific scenarios with specific conditions with the selected field of view and perspective of the cameras used. Alternatively, three-dimensional computer modeling and physically-based rendering (PBR) can be used to recreate an accident scene geometry and lighting conditions. PBR is a rendering method to create synthetic images and video by accurately simulating how light interacts in the three-dimensional environment. Specifically, the process presented in this paper utilizes the Cycles render engine within Blender. This allows for the accident scene to be recreated in a three-dimensional environment including the natural and artificial light sources. As we are concerned with accurately representing the light in the scene, it is necessary to create light sources within Cycles that represent the real-world light sources. The light sources in Cycles are quantified by several variables, including strength, color, and size. The strength and size variables determine the self-emitted radiance of the light source and requires further explanation to determine the relationship between these variables in Cycles and real-world lighting quantities. The color variable describes the light color as either an RGB value or as a color temperature value. In this paper, we define and validate the relationship between strength units in Cycles and photometric quantities and illustrate that the lighting produced is based on the physics of light.