Power of 2

Author: tzaeschke

src/main/java/org/tinspin/index/qthypercube/QuadTreeKD.java

@@ -21,6 +21,7 @@
 import java.util.function.Predicate;
 
 import org.tinspin.index.*;
+import org.tinspin.index.util.MathTools;
 import org.tinspin.index.util.StringBuilderLn;
 
 /**
@@ -94,7 +95,9 @@ public void insert(double[] key, T value) {
 		PointEntry<T> e = new PointEntry<>(key, value);
 		if (root == null) {
 			// We calculate a better radius when adding a second point.
-			root = new QNode<>(key.clone(), INITIAL_RADIUS);
+			// We align the center to a power of two. That reduces precision problems when
+			// creating subnode centers.
+			root = new QNode<>(MathTools.floorPowerOfTwoCopy(key), INITIAL_RADIUS);
 		}
 		if (root.getRadius() == INITIAL_RADIUS) {
 			adjustRootSize(key);
@@ -113,10 +116,17 @@ private void adjustRootSize(double[] key) {
 			return;
 		}
 		if (root.getRadius() == INITIAL_RADIUS) {
-			// We just use Euclidean here, that should be good enough in all cases.
-			double dist = PointDistance.L2.dist(key, root.getCenter());
-			if (dist > 0) {
-				root.adjustRadius(2 * dist);
+			// Root size has not been initialized yet.
+			// We start by getting the maximum horizontal distance between the node center and any point in the node
+			double dMax = MathTools.maxDelta(key, root.getCenter());
+			for (int i = 0; i < root.getEntries().size(); i++) {
+				dMax = Math.max(dMax, MathTools.maxDelta(root.getEntries().get(i).point(), root.getCenter()));
+			}
+			// We calculate the minimum required radius that is also a power of two.
+			// This radius can be divided by 2 many times without precision problems.
+			double radius = MathTools.ceilPowerOfTwo(dMax + QUtil.EPS_MUL);
+			if (radius > 0) {
+				root.adjustRadius(radius);
 			} else if (root.getEntries().size() >= maxNodeSize - 1) {
 				// we just set an arbitrary radius here
 				root.adjustRadius(1000);

src/main/java/org/tinspin/index/qthypercube2/QuadTreeKD2.java

@@ -109,6 +109,8 @@ public void insert(double[] key, T value) {
 		PointEntry<T> e = new PointEntry<>(key, value);
 		if (root == null) {
 			// We calculate a better radius when adding a second point.
+			// We align the center to a power of two. That reduces precision problems when
+			// creating subnode centers.
 			root = new QNode<>(MathTools.floorPowerOfTwoCopy(key), INITIAL_RADIUS);
 		}
 		if (root.getRadius() == INITIAL_RADIUS) {
@@ -128,10 +130,14 @@ private void adjustRootSize(double[] key) {
 			return;
 		}
 		if (root.getRadius() == INITIAL_RADIUS) {
+			// Root size has not been initialized yet.
+			// We start by getting the maximum horizontal distance between the node center and any point in the node
 			double dMax = MathTools.maxDelta(key, root.getCenter());
 			for (int i = 0; i < root.getValueCount(); i++) {
 				dMax = Math.max(dMax, MathTools.maxDelta(root.getValues()[i].point(), root.getCenter()));
 			}
+			// We calculate the minimum required radius that is also a power of two.
+			// This radius can be divided by 2 many times without precision problems.
 			double radius = MathTools.ceilPowerOfTwo(dMax + QUtil.EPS_MUL);
 			if (radius > 0) {
 				root.adjustRadius(radius);