When users want to plan the reconstructed virtual scenes

if we obtained the information of the lighting at the time when the images were taken

we can use the rendering technologies from computer graphics to obtain new synthesized photorealistic imageries. This paper presents techniques for recovering the tilt angle of solar illuminant from a single outdoor building image

which can be integrated to most current image-base architectural rebuilding systems. Solar illumination can be treated as parallel light. Its direction can be measured by tilt and slant angle in architectural coordinate system. To calculate the tilt angle

we utilize the changes of intensities from different wall surfaces. This idea comes from SFS (Shape from Shading) technique. On the basis of the calculated tilt angle

we can easily calculate the slant angle from images by using the bulges of the wall surface and their shadows.