/**
* Return a polygon which is the union of the given polygons; combines
* vertices that form edges that are almost identical, as defined by
* vertexMergeRadius. Note: clears the List!
*/
public static S2Polygon DestructiveUnionSloppy(System.Collections.Generic.ICollection <S2Polygon> polygons, S1Angle vertexMergeRadius)
{
// Effectively create a priority queue of polygons in order of number of
// vertices. Repeatedly union the two smallest polygons and add the result
// to the queue until we have a single polygon to return.
// map: # of vertices -> polygon
//TreeMultimap<Integer, S2Polygon> queue = TreeMultimap.create();
var queue = new MultiMap <int, S2Polygon>();
foreach (var polygon in polygons)
{
queue.Add(polygon.NumVertices, polygon);
}
polygons.Clear();
// Java uses a live-view that maps to the underlying structure
//Set<Map.Entry<Integer, S2Polygon>> queueSet = queue.entries();
var enumer = queue.SortedValues;
while (queue.CountIsAtLeast(2))
{
// Pop two simplest polygons from queue.
// queueSet = queue.entries();
//Iterator<Map.Entry<Integer, S2Polygon>> smallestIter = queueSet.iterator();
var smallestTwo = enumer.Take(2).ToList();
//Map.Entry<Integer, S2Polygon> smallest = smallestIter.next();
//int aSize = smallest.getKey().intValue();
//S2Polygon aPolygon = smallest.getValue();
//smallestIter.remove();
//smallest = smallestIter.next();
//int bSize = smallest.getKey().intValue();
//S2Polygon bPolygon = smallest.getValue();
//smallestIter.remove();
foreach (var item in smallestTwo)
{
queue.Remove(item);
}
// Union and add result back to queue.
var unionPolygon = new S2Polygon();
unionPolygon.InitToUnionSloppy(smallestTwo[0].Value, smallestTwo[1].Value, vertexMergeRadius);
var unionSize = smallestTwo[0].Key + smallestTwo[1].Key;
queue.Add(unionSize, unionPolygon);
// We assume that the number of vertices in the union polygon is the
// sum of the number of vertices in the original polygons, which is not
// always true, but will almost always be a decent approximation, and
// faster than recomputing.
}
if (queue.Count == 0)
{
return(new S2Polygon());
}
else
{
//return queue.get(queue.asMap().firstKey()).first();
return(queue.SortedValues.First().Value);
}
}