Fast Photo-Realistic Rendering of Trees in Daylight

We propose a fast approach for photo-realistic rendering of trees under various kinds of daylight, which is particularly useful for the environmental assessment of landscapes. In our approach the 3D tree models are transformed to a quasi-3D tree database registering geometrical and shading information of tree surfaces, i.e. their normal vectors, relative depth, and shadowing of direct sunlight and skylight, by using a combination of 2D buffers. Thus the rendering speed of quasi-3D trees depends on their display sizes only, regardless of the complexity of their original 3D tree models. By utilizing a two-step shadowing algorithm, our proposed method can create high quality forest scenes illuminated by both sunlight and skylight at a low cost. It can generate both umbrae and penumbrae on a tree cast by other trees and any other objects such as buildings or clouds. Transparency, specular reflection and inter-reflection of leaves, which influence the delicate shading effects of trees, can also be simulated with verisimilitude.