=== Wedge Diffraction From Edges ===
[[File:diffract.png|thumb|350px|The Incident Ray and Diffract Ray Cone at the Edge of a Building]]
For the purpose of calculation of diffraction from building edges, we define a "Wedge" as having two faces, the 0-face and the ''n''-face. The wedge angle is a = (2-''n'')p, where the parameter ''n'' is required for the calculation of diffraction coefficients. All the diffracted rays lie on a cone with its vertex at the diffraction point and a wedge angle equal to the angle of incidence in the opposite direction. A diffracted ray is assumed to originate from a virtual image source point. Three triplets of unit vectors are defined as follows:
where the resolution of the angle θ<sub>w</sub> is chosen to be the same as the resolution of the incident ray.
[[File:diffract.png]]
Figure: The Incident Ray and Diffract Ray Cone at the Edge of a Building
The other unit vectors for the incident and diffracted rays are found as: