By Justin Doughty
Grading requires geometry to grade from. Surfaces have too many points for it to know where to stop or start automatically, so some form of horizontal “line” geometry is needed.
To grade from the boundary of one surface down or up to another, select the surface with the required boundary and use Extract from Surface>Extract Objects, and select the border:
This will create a 3D polyline that can then be converted to a Featureline for grading.
Alternatively a Featureline can be drawn, using the levels from a surface (SU), or snapping to the triangulation of the surface can be used.