intersectHeight: Calculates where the segments of a polygon intersect a...
In tunelipt/model3d: Funções para manipulação de modelos 3D.

Given a polygone, if one wants to chop it at a given height, it is important to figure out which segments of the polygon cross this height. This function identifies which segments cross the height. One point should be remembered: sometimes a vertex has height h. In this case it should be handled differently. Edges that cross the height h are identified by flag 1. If the first vertex of the edge intersects the height, the edge is identified by flag 2. Otherwise the edge is identifed by flag 0