/// <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="rectCoordinate">The <see cref="HyperRectCoordinate{TDimension}"/> containing the possible nearest neighbors.</param>
/// <param name="dimension">The current splitting dimension for this recursion branch.</param>
/// <param name="nearestNeighbors">The <see cref="BoundedPriorityListCoordinate{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,
HyperRectCoordinate <TDimension> rectCoordinate,
int dimension,
BoundedPriorityListCoordinate <int, double> nearestNeighbors,
double maxSearchRadiusSquared)
{
if (this.InternalTreeOfPoints.Length <= nodeIndex || nodeIndex < 0 || this.InternalTreeOfPoints[nodeIndex] == null)
{
return;
}
// Work out the current dimension
var dim = dimension % this.Dimensions;
var leftRect = rectCoordinate.Clone();
var rightRect = rectCoordinate.Clone();
if (dim == 0)
{
leftRect.MaxPoint.Latitude = this.InternalTreeOfPoints[nodeIndex].Latitude;
rightRect.MinPoint.Latitude = this.InternalTreeOfPoints[nodeIndex].Latitude;
}
if (dim == 1)
{
leftRect.MaxPoint.Longitude = this.InternalTreeOfPoints[nodeIndex].Longitude;
rightRect.MinPoint.Longitude = this.InternalTreeOfPoints[nodeIndex].Longitude;
}
// Determine which side the target resides in
var compare = dim == 0 ? target.Latitude.CompareTo(this.InternalTreeOfPoints[nodeIndex].Latitude)
: target.Longitude.CompareTo(this.InternalTreeOfPoints[nodeIndex].Longitude);
var nearerRect = compare <= 0 ? leftRect : rightRect;
var furtherRect = compare <= 0 ? rightRect : leftRect;
var nearerNode = compare <= 0 ? BinaryTreeNavigationCoordinate.LeftChildIndex(nodeIndex) : BinaryTreeNavigationCoordinate.RightChildIndex(nodeIndex);
var furtherNode = compare <= 0 ? BinaryTreeNavigationCoordinate.RightChildIndex(nodeIndex) : BinaryTreeNavigationCoordinate.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.InternalTreeOfPoints[nodeIndex], target);
if (distanceSquaredToTarget.CompareTo(maxSearchRadiusSquared) <= 0 && this.InternalTreeOfPoints[nodeIndex].Used == false)
{
nearestNeighbors.Add(nodeIndex, distanceSquaredToTarget);
}
}
