long time fan / first time poster here!
My question: is there an efficient algorithm for isolating just the downward-facing faces of a 3D convex hull?
In two dimensions, if one draws a line from the rightmost point on the hull to the leftmost point on the hull, that line will definitionally serve to part the upward-facing lines on the hull from the downward-facing lines, i.e. separate the lower hull from the upper hull.
Does anyone know an analogue in 3D? I know people do this all the time, because the lower hull is used in Delaunay triangulation, and the lower hull is used in thermodynamics, but I haven't been able to track down a description of how to do it in 3D.
Any help or references would be sincerely appreciated!