/// <summary>
/// Returns the {@link Node} at the given location,
/// or null if no {@link Node} was there.
/// </summary>
/// <param name="pt">the location to query
/// </param>
/// <returns> the node found
/// </returns>
/// <returns>
/// <c>null</c> if this graph contains no node at the location
/// </returns>
public Node FindNode(Coordinate pt)
{
return((Node)nodeMap.Find(pt));
}