3.1. Beam number determination

As shown in Figure 4, the incident light starting point was selected at point A, and then each light beam increased a distance of <sup>2</sup><sup>H</sup> <sup>n</sup> tan <sup>α</sup> at x-axis direction, and ended at point C. Different weighted reflectance γ according to the flow chart were carried out when n was set to different values. γ can achieve exact value when n is larger than a certain value. The calculation results under the model with no fillet (<sup>θ</sup> <sup>¼</sup> <sup>55</sup><sup>∘</sup> , r ¼ 0) on the included angle and the model with a fillet (<sup>θ</sup> <sup>¼</sup> <sup>55</sup><sup>∘</sup> , r ¼ H=10) on the included angle were shown in Table 1 and Table 2 respectively.

A satisfactory result was obtained at n ¼ 200, following works were carried out at the condition of n ¼ 200. At n ¼ 200, the relative errors between the adjacent dates were 0.148% and �0.491% respectively which can meet the needs of engineering completely.
