rtrace_dc is a modified version of the RADIANCE program rtrace. It has equivalent functionality on that it can calculate several daylight coefficients at the same time. It has two additional modes:
-N <int> -Dm with int<=148: These options allow the calculation of 145 diffuse daylight using a Tregenza sky distribution and 3 ground daylight coefficients.
-N <int> -Dc with int<=148: These options allow the calculation of around 65 direct daylight coefficients for direct sun positions that are located along typical solar paths throughout the year.