polygonalObstacles

Obstacles represented as ConvexPolygons, are assumed to be mutable but limited to the extension (i.e. they can only grow, not shrink). This is the behavior of seeds used by NaviGator.generateNavigationGraph, making this assumption allows to cache useful data such as whether an edge can still advance or an obstacle has already been encountered. This is a var but is assumed to be set only once before starting to extend this polygon.