/// <summary>
/// Returns the closest node between currentBest and CurrentNode to point
/// </summary>
private KDTreeNode <T> getClosestToPoint(IDistanceCalculator <T> distanceCalculator,
KDTreeNode <T> currentBest, KDTreeNode <T> currentNode, T[] point)
{
if (distanceCalculator.Compare(currentBest.Points,
currentNode.Points, point) < 0)
{
return(currentBest);
}
return(currentNode);
}
/// <summary>
/// Recursively find leaf node to insert
/// at each level comparing against the next dimension.
/// </summary>
private KDTreeNode <T> findNearestNeighbour(KDTreeNode <T> currentNode,
T[] searchPoint, int depth,
IDistanceCalculator <T> distanceCalculator)
{
var currentDimension = depth % dimensions;
KDTreeNode <T> currentBest = null;
var compareResult = searchPoint[currentDimension]
.CompareTo(currentNode.Points[currentDimension]);
//move toward search point until leaf is reached
if (compareResult < 0)
{
if (currentNode.Left != null)
{
currentBest = findNearestNeighbour(currentNode.Left,
searchPoint, depth + 1, distanceCalculator);
}
else
{
currentBest = currentNode;
}
//currentBest is greater than point to current node distance
//or if right node sits on split plane
//then also move left
if (currentNode.Right != null &&
(distanceCalculator.Compare(currentNode.Points[currentDimension], searchPoint[currentDimension], searchPoint, currentBest.Points) < 0 ||
currentNode.Right.Points[currentDimension]
.CompareTo(currentNode.Points[currentDimension]) == 0))
{
var rightBest = findNearestNeighbour(currentNode.Right,
searchPoint, depth + 1,
distanceCalculator);
currentBest = getClosestToPoint(distanceCalculator, currentBest, rightBest, searchPoint);
}
//now recurse up from leaf updating current Best
currentBest = getClosestToPoint(distanceCalculator, currentBest, currentNode, searchPoint);
}
else if (compareResult >= 0)
{
if (currentNode.Right != null)
{
currentBest = findNearestNeighbour(currentNode.Right,
searchPoint, depth + 1, distanceCalculator);
}
else
{
currentBest = currentNode;
}
//currentBest is greater than point to current node distance
//or if search point lies on split plane
//then also move left
if (currentNode.Left != null &&
(distanceCalculator.Compare(currentNode.Points[currentDimension], searchPoint[currentDimension], searchPoint, currentBest.Points) < 0 || compareResult == 0))
{
var leftBest = findNearestNeighbour(currentNode.Left,
searchPoint, depth + 1,
distanceCalculator);
currentBest = getClosestToPoint(distanceCalculator, currentBest, leftBest, searchPoint);
}
//now recurse up from leaf updating current Best
currentBest = getClosestToPoint(distanceCalculator, currentBest, currentNode, searchPoint);
}
return(currentBest);
}
