An algorithm focusing on the occlusions between rays and NURBS surfaces is presented in this paper,where simple geometrical principle which makes the algorithm adequate in possible cases is used. When the ray starts from or ends on the surface,the self-shadowing is also taken into account. The algorithm given can be applied to optical methods like PO GTD or UTD in electromagnetic calculation where shadowing is of key problem and especially when the NURBS modeling is introduced.
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