/// <summary>
/// Searches for the closest points in a hyper-sphere around the given center.
/// </summary>
/// <param name="center">The center of the hyper-sphere</param>
/// <param name="radius">The radius of the hyper-sphere</param>
/// <param name="neighboors">The number of neighbors to return.</param>
/// <returns>The specified number of closest points in the hyper-sphere</returns>
public List <TNode> NearestNeighborsRadial(TDimension[] center, double radius, int neighboors = -1)
{
var nearestNeighbors = new BoundedPriorityList <int, double>(neighboors == -1 ? this.Count : neighboors, false);
var rect = HyperRect <TDimension> .Infinite(this.Dimensions, this.MaxValue, this.MinValue);
this.SearchForNearestNeighbors(0, center, rect, 0, nearestNeighbors, radius);
return(nearestNeighbors.ToResultSetRadial(this, neighboors));
}
/// <summary>
/// Finds the nearest neighbors in the <see cref="KDTree{TDimension,TNode}"/> of the given <paramref name="point"/>.
/// </summary>
/// <param name="point">The point whose neighbors we search for.</param>
/// <param name="neighbors">The number of neighbors to look for.</param>
/// <returns>The</returns>
public List <TNode> NearestNeighborsLinear(TDimension[] point, int neighbors)
{
var nearestNeighbors = new BoundedPriorityList <int, double>(neighbors, true);
var rect = HyperRect <TDimension> .Infinite(this.Dimensions, this.MaxValue, this.MinValue);
this.SearchForNearestNeighbors(0, point, rect, 0, nearestNeighbors, double.MaxValue);
return(nearestNeighbors.ToResultSet(this));
}
/// <summary>
/// A top-down recursive method to find the nearest neighbors of a given point.
/// </summary>
/// <param name="nodeIndex">The index of the node for the current recursion branch.</param>
/// <param name="target">The point whose neighbors we are trying to find.</param>
/// <param name="rect">The <see cref="HyperRect{T}"/> containing the possible nearest neighbors.</param>
/// <param name="dimension">The current splitting dimension for this recursion branch.</param>
/// <param name="nearestNeighbors">The <see cref="BoundedPriorityList{TElement,TPriority}"/> containing the nearest neighbors already discovered.</param>
/// <param name="maxSearchRadiusSquared">The squared radius of the current largest distance to search from the <paramref name="target"/></param>
private void SearchForNearestNeighbors(
int nodeIndex,
TDimension[] target,
HyperRect <TDimension> rect,
int dimension,
BoundedPriorityList <int, double> nearestNeighbors,
double maxSearchRadiusSquared)
{
if (this.InternalPointArray.Length <= nodeIndex || nodeIndex < 0 ||
this.InternalPointArray[nodeIndex] == null)
{
return;
}
// Work out the current dimension
var dim = dimension % this.Dimensions;
var leftRect = rect.Clone();
leftRect.MaxPoint[dim] = this.InternalPointArray[nodeIndex][dim];
var rightRect = rect.Clone();
rightRect.MinPoint[dim] = this.InternalPointArray[nodeIndex][dim];
// Determine which side the target resides in
var compare = target[dim].CompareTo(this.InternalPointArray[nodeIndex][dim]);
var nearerRect = compare <= 0 ? leftRect : rightRect;
var furtherRect = compare <= 0 ? rightRect : leftRect;
var nearerNode = compare <= 0 ? BinaryTreeNavigation.LeftChildIndex(nodeIndex) : BinaryTreeNavigation.RightChildIndex(nodeIndex);
var furtherNode = compare <= 0 ? BinaryTreeNavigation.RightChildIndex(nodeIndex) : BinaryTreeNavigation.LeftChildIndex(nodeIndex);
// Move down into the nearer branch
this.SearchForNearestNeighbors(
nearerNode,
target,
nearerRect,
dimension + 1,
nearestNeighbors,
maxSearchRadiusSquared);
// Walk down into the further branch but only if our capacity hasn't been reached
// OR if there's a region in the further rectangle that's closer to the target than our
// current furtherest nearest neighbor
var closestPointInFurtherRect = furtherRect.GetClosestPoint(target);
var distanceSquaredToTarget = this.Metric(closestPointInFurtherRect, target);
if (distanceSquaredToTarget.CompareTo(maxSearchRadiusSquared) <= 0)
{
if (nearestNeighbors.IsFull)
{
if (distanceSquaredToTarget.CompareTo(nearestNeighbors.MaxPriority) < 0)
{
this.SearchForNearestNeighbors(
furtherNode,
target,
furtherRect,
dimension + 1,
nearestNeighbors,
maxSearchRadiusSquared);
}
}
else
{
this.SearchForNearestNeighbors(
furtherNode,
target,
furtherRect,
dimension + 1,
nearestNeighbors,
maxSearchRadiusSquared);
}
}
// Try to add the current node to our nearest neighbors list
distanceSquaredToTarget = this.Metric(this.InternalPointArray[nodeIndex], target);
if (distanceSquaredToTarget.CompareTo(maxSearchRadiusSquared) <= 0 && this.InternalNodeArray[nodeIndex].Used == false)
{
nearestNeighbors.Add(nodeIndex, distanceSquaredToTarget);
}
}