Abstract
Computing the correct illumination of virtual scenes is a well-explored area today. Most commonly used 3D graphic libraries like OpenGL or DirectX/Direct3d contain functions for these tasks. The "Shadow Catcher" approach uses the shadows that a light source casts on a so-called "sensor geometry" to determine the position of the light source by analyzing the shape of those shadows. Position and shape of this geometry are known by the system. ARToolKit is currently used to track the position of the geometry, but the solution is independent of the underlying tracking system. The system uses computer vision methodologies to detect shadow silhouettes on the surface of this geometry. The knowledge about the geometry's shape, together with the information about the shadow silhouettes, is used to compute the position of the light source.