public KdTreeNode <TKey, TValue>[] RadialSearch(TKey[] center, TKey radius, int count)
{
var nearestNeighbours = new NearestNeighbourList <KdTreeNode <TKey, TValue>, TKey>(count);
this.AddNearestNeighbours(this.root,
center,
HyperRect <TKey> .Infinite(this.dimensions),
0,
nearestNeighbours,
(Number <TKey>)radius * radius);
count = nearestNeighbours.Count;
var neighbourArray = new KdTreeNode <TKey, TValue> [count];
for (var index = 0; index < count; index++)
{
neighbourArray[count - index - 1] = nearestNeighbours.RemoveFurtherest();
}
return(neighbourArray);
}
public KdTreeNode <TKey, TValue>[] GetNearestNeighbours(TKey[] point, int count)
{
if (count > Count)
{
count = Count;
}
if (count < 0)
{
throw new ArgumentException("Number of neighbors cannot be negative");
}
if (count == 0)
{
return(new KdTreeNode <TKey, TValue> [0]);
}
var neighbours = new KdTreeNode <TKey, TValue> [count];
var nearestNeighbours = new NearestNeighbourList <KdTreeNode <TKey, TValue>, TKey>(count);
var rect = HyperRect <TKey> .Infinite(dimensions);
AddNearestNeighbours(root, point, rect, 0, nearestNeighbours, Number <TKey> .MaxValue);
count = nearestNeighbours.Count;
var neighbourArray = new KdTreeNode <TKey, TValue> [count];
for (var index = 0; index < count; index++)
{
neighbourArray[count - index - 1] = nearestNeighbours.RemoveFurtherest();
}
return(neighbourArray);
}
/*
* 1. Search for the target
*
* 1.1 Start by splitting the specified hyper rect
* on the specified node's point along the current
* dimension so that we end up with 2 sub hyper rects
* (current dimension = depth % dimensions)
*
* 1.2 Check what sub rectangle the the target point resides in
* under the current dimension
*
* 1.3 Set that rect to the nearer rect and also the corresponding
* child node to the nearest rect and node and the other rect
* and child node to the further rect and child node (for use later)
*
* 1.4 Travel into the nearer rect and node by calling function
* recursively with nearer rect and node and incrementing
* the depth
*
* 2. Add leaf to list of nearest neighbours
*
* 3. Walk back up tree and at each level:
*
* 3.1 Add node to nearest neighbours if
* we haven't filled our nearest neighbour
* list yet or if it has a distance to target less
* than any of the distances in our current nearest
* neighbours.
*
* 3.2 If there is any point in the further rectangle that is closer to
* the target than our furtherest nearest neighbour then travel into
* that rect and node
*
* That's it, when it finally finishes traversing the branches
* it needs to we'll have our list!
*/
private void AddNearestNeighbours(
KdTreeNode <TKey, TValue> node,
TKey[] target,
HyperRect <TKey> rect,
int depth,
NearestNeighbourList <KdTreeNode <TKey, TValue>, TKey> nearestNeighbours,
TKey maxSearchRadiusSquared)
{
if (node == null)
{
return;
}
// Work out the current dimension
int dimension = depth % dimensions;
// Split our hyper-rect into 2 sub rects along the current
// node's point on the current dimension
var leftRect = rect.Clone();
leftRect.MaxPoint[dimension] = node.Point[dimension];
var rightRect = rect.Clone();
rightRect.MinPoint[dimension] = node.Point[dimension];
// Which side does the target reside in?
int compare = target[dimension].CompareTo(node.Point[dimension]);
var nearerRect = compare <= 0 ? leftRect : rightRect;
var furtherRect = compare <= 0 ? rightRect : leftRect;
var nearerNode = compare <= 0 ? node.LeftChild : node.RightChild;
var furtherNode = compare <= 0 ? node.RightChild : node.LeftChild;
// Let's walk down into the nearer branch
if (nearerNode != null)
{
AddNearestNeighbours(
nearerNode,
target,
nearerRect,
depth + 1,
nearestNeighbours,
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 rect that's closer to the target than our
// current furtherest nearest neighbour
TKey[] closestPointInFurtherRect = furtherRect.GetClosestPoint(target);
TKey distanceSquaredToTarget =
closestPointInFurtherRect.Select(
(t, i) => (Number <TKey>)t - target[i]).
Aggregate(default(TKey),
(current, val) => (Number <TKey>)current + (Number <TKey>)val * val);
if (distanceSquaredToTarget.CompareTo(maxSearchRadiusSquared) <= 0)
{
if (nearestNeighbours.IsCapacityReached)
{
if (distanceSquaredToTarget.CompareTo(nearestNeighbours.GetFurtherestDistance()) < 0)
{
this.AddNearestNeighbours(
furtherNode,
target,
furtherRect,
depth + 1,
nearestNeighbours,
maxSearchRadiusSquared);
}
}
else
{
this.AddNearestNeighbours(
furtherNode,
target,
furtherRect,
depth + 1,
nearestNeighbours,
maxSearchRadiusSquared);
}
}
// Try to add the current node to our nearest neighbours list
distanceSquaredToTarget =
node.Point.Select((t, i) => (Number <TKey>)t - target[i]).
Aggregate(default(TKey),
(current, val) => (Number <TKey>)current + (Number <TKey>)val * val);
if (distanceSquaredToTarget.CompareTo(maxSearchRadiusSquared) <= 0)
{
nearestNeighbours.Add(node, distanceSquaredToTarget);
}
}
