private void nearest(KDTreeNode <T> current, double[] position, KdTreeNodeCollection <T> list)
{
// Compute distance from this node to the point
double d = _distance(position, current.Position);
if (current.IsLeaf)
{
// Base: node is leaf
list.Add(current, d);
}
else
{
// Check for leafs on the opposite sides of
// the subtrees to nearest possible neighbors.
// Prepare for recursion. The following null checks
// will be used to avoid function calls if possible
double value = position[current.Axis];
double median = current.Position[current.Axis];
if (value < median)
{
if (current.Left != null)
{
nearest(current.Left, position, list);
}
list.Add(current, d);
if (current.Right != null)
{
if (Math.Abs(value - median) <= list.Distance.Max)
{
nearest(current.Right, position, list);
}
}
}
else
{
if (current.Right != null)
{
nearest(current.Right, position, list);
}
list.Add(current, d);
if (current.Left != null)
{
if (Math.Abs(value - median) <= list.Distance.Max)
{
nearest(current.Left, position, list);
}
}
}
}
}
/// <summary>
/// Retrieves a fixed point of nearest points to a given point.
/// </summary>
///
/// <param name="position">The queried point.</param>
/// <param name="neighbors">The number of neighbors to retrieve.</param>
///
/// <returns>A list of neighbor points, ordered by distance.</returns>
///
public KdTreeNodeCollection <T> Nearest(double[] position, int neighbors)
{
var list = new KdTreeNodeCollection <T>(size: neighbors);
if (root != null)
{
nearest(root, position, list);
}
return(list);
}
/// <summary>
/// Retrieves the nearest points to a given point within a given radius.
/// </summary>
///
/// <param name="position">The queried point.</param>
/// <param name="radius">The search radius.</param>
/// <param name="maximum">The maximum number of neighbors to retrieve.</param>
///
/// <returns>A list of neighbor points, ordered by distance.</returns>
///
public KdTreeNodeCollection <T> Nearest(double[] position, double radius, int maximum)
{
var list = new KdTreeNodeCollection <T>(maximum);
if (root != null)
{
nearest(root, position, radius, list);
}
return(list);
}
/// <summary>
/// Retrieves a fixed point of nearest points to a given point.
/// </summary>
///
/// <param name="position">The queried point.</param>
/// <param name="neighbors">The number of neighbors to retrieve.</param>
/// <param name="maxLeaves">The maximum number of leaf nodes that can
/// be visited before the search finishes with an approximate answer.</param>
///
/// <returns>A list of neighbor points, ordered by distance.</returns>
///
public KdTreeNodeCollection <T> ApproximateNearest(double[] position, int neighbors, int maxLeaves)
{
var list = new KdTreeNodeCollection <T>(size: neighbors);
if (root != null)
{
int visited = 0;
approximate(root, position, list, maxLeaves, ref visited);
}
return(list);
}
private bool approximate(KDTreeNode <T> current, double[] position,
KdTreeNodeCollection <T> list, int maxLeaves, ref int visited)
{
// Compute distance from this node to the point
double d = _distance(position, current.Position);
if (current.IsLeaf)
{
// Base: node is leaf
list.Add(current, d);
visited++;
if (visited > maxLeaves)
{
return(true);
}
}
else
{
// Check for leafs on the opposite sides of
// the subtrees to nearest possible neighbors.
// Prepare for recursion. The following null checks
// will be used to avoid function calls if possible
double value = position[current.Axis];
double median = current.Position[current.Axis];
if (value < median)
{
if (current.Left != null)
{
if (approximate(current.Left, position, list, maxLeaves, ref visited))
{
return(true);
}
}
list.Add(current, d);
if (current.Right != null)
{
if (Math.Abs(value - median) <= list.Distance.Max)
{
if (approximate(current.Right, position, list, maxLeaves, ref visited))
{
return(true);
}
}
}
}
else
{
if (current.Right != null)
{
approximate(current.Right, position, list, maxLeaves, ref visited);
}
list.Add(current, d);
if (current.Left != null)
{
if (Math.Abs(value - median) <= list.Distance.Max)
{
if (approximate(current.Left, position, list, maxLeaves, ref visited))
{
return(true);
}
}
}
}
}
return(false);
}
