getDepth method
Implementation
int getDepth(Coordinate p) {
List stabbedSegments = findStabbedSegments(p);
// if no segments on stabbing line subgraph must be outside all others.
if (stabbedSegments.isEmpty) return 0;
var sorted = List.from(stabbedSegments);
sorted.sort((o1, o2) => o1.compareTo(o2));
DepthSegment ds = sorted.first; // min is requested
return ds.leftDepth;
}