/// <summary>
/// "invalid" value will be returned by queries if no valid result is found (eg bounded-distance query)
/// </summary>
public PointHashGrid2d(double cellSize, T invalidValue)
{
Hash = new Dictionary <Vector2i, List <T> >();
Indexer = new ScaleGridIndexer2()
{
CellSize = cellSize
};
spinlock = new SpinLock();
this.invalidValue = invalidValue;
}