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);
list.Add(current, d);
if (++visited > maxLeaves)
{
return(true);
}
// 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];
double u = value - median;
if (u <= 0)
{
if (current.Left != null)
{
if (approximate(current.Left, position, list, maxLeaves, ref visited))
{
return(true);
}
}
if (current.Right != null && Math.Abs(u) <= list.Maximum)
{
if (approximate(current.Right, position, list, maxLeaves, ref visited))
{
return(true);
}
}
}
else
{
if (current.Right != null)
{
approximate(current.Right, position, list, maxLeaves, ref visited);
}
if (current.Left != null && Math.Abs(u) <= list.Maximum)
{
if (approximate(current.Left, position, list, maxLeaves, ref visited))
{
return(true);
}
}
}
return(false);
}
/// <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);
}
/// <summary>
/// k-nearest neighbors search.
/// </summary>
///
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);
list.Add(current, d);
// 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];
double u = value - median;
if (u <= 0)
{
if (current.Left != null)
{
nearest(current.Left, position, list);
}
if (current.Right != null && Math.Abs(u) <= list.Maximum)
{
nearest(current.Right, position, list);
}
}
else
{
if (current.Right != null)
{
nearest(current.Right, position, list);
}
if (current.Left != null && Math.Abs(u) <= list.Maximum)
{
nearest(current.Left, position, list);
}
}
}
