Presentation of the hemisphere method
Pierre Vueghs, Pierre Beckers · WIT transactions on engineering sciences · 2006
In the field of image synthesis or thermal radiation, the challenge is to calculate the radiative exchanges between the surfaces of the model.To quantify the interactions between the surfaces, we define a number called view factor, noted F ij .The view factor represents the fraction of the diffusely emitted power from a surface A i which reaches a surface A j .The calculation of the view factors is a very difficult problem.A method has been designed in image synthesis and also applied to thermal problems.This method, called hemi cube, uses a cube as a screen onto which all the scene is projected.Here, we present another method that we have named hemisphere, where the surface of projection is the unit sphere surrounded by the hemi cube.This projection, based on the Nusselt's Analogy, is simpler and more natural than the hemi cube's projection.We show in this paper that the hemisphere method is faster and more efficient than the hemi cube.In this paper, we present a tessellation of the hemisphere into cells characterized by an equal elementary view factor.This allows us to avoid over sampling and to save computation time.We show that this method is faster and more efficient than the classic hemi cube.We present also some results that illustrate the efficiency of the hemisphere method.