“…For indoor environments, however, these methods must be implemented in a three-dimensional code, for which the number of traced rays becomes critical, as it is directly related to required computation times [3]. Various techniques have been proposed to reduce the number of traced rays, like the use of a receiving sphere [4], or the big ray tracing technique [5][6][7]. For the same goal, this Letter proposes another technique, which allows sufficiently accurate, fast computation of fields in a multireflecting environment.…”