This document explains how the delivered Ditch_Cut_Tight and Ditch_Fill_Tight templates are built.
Cut or fill ditches can be defined by a template seeking the existing ground twice, once for the cut or fill slope and again for the outside ditch slope. These dual-seek templates only provide an optimum solution if the existing ground is level across the ditch. If the ground is not level, the ditch backslope is either too high, which consumes unnecessary width, or is too low, which fails to provide enough depth.
Targeting the surface for the inside wall of the ditch is actually unnecessary: generally there is no need in the final solution to tie the inside ditch wall to where the existing surface used to be. The true requirement is to provide the required ditch in the narrowest footprint.
Exterior ditch solutions generally have one variable: the length of the cut or fill slope; the rest of the geometry is fixed. The trick to building a single-seek template is to position the origin of the seeking segment at a horizontal and vertical offset equivalent to the fixed geometry, which in simple cases is the ditch. From this offset origin the seek point finds the Daylight point.
Once the Daylight point is found, enough information exists to build the exterior ditch components to its inside.