BallTree WIP

Author: tzaeschke

src/main/java/org/tinspin/index/balltree/BTNode.java

@@ -0,0 +1,193 @@
+/*
+ * Copyright 2016-2017 Tilmann Zaeschke
+ *
+ * This file is part of TinSpin.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.tinspin.index.balltree;
+
+import org.tinspin.index.Index;
+import org.tinspin.index.PointDistance;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import static org.tinspin.index.Index.BoxEntry;
+
+class BTUtil {
+
+    static final double EPS_MUL = 1.000000001;
+
+    private BTUtil() {
+    }
+
+    public static boolean isPointEnclosed(double[] point, double[] min, double[] max) {
+        for (int d = 0; d < min.length; d++) {
+            if (point[d] < min[d] || point[d] > max[d]) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+
+    /**
+     * The tests for inclusion with UPPER BOUNDARY EXCLUSIVE!
+     * I.e. it firs only if point is SMALLER than (center + radius).
+     */
+    public static boolean fitsIntoNode(double[] point, double[] center, double radius) {
+        return PointDistance.l2(point, center) <= radius;
+    }
+
+    public static boolean isPointEqual(double[] p1, double[] p2) {
+        for (int d = 0; d < p1.length; d++) {
+            if (p1[d] != p2[d]) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+//    public static boolean isRectEqual(double[] p1L, double[] p1U, double[] p2L, double[] p2U) {
+//        return isPointEqual(p1L, p2L) && isPointEqual(p1U, p2U);
+//    }
+//
+//    public static <T> boolean isRectEqual(BoxEntry<T> e, double[] keyL, double[] keyU) {
+//        return isRectEqual(e.min(), e.max(), keyL, keyU);
+//    }
+//
+//    public static <T> boolean isRectEqual(BoxEntry<T> e, BoxEntry<T> e2) {
+//        return isRectEqual(e.min(), e.max(), e2.min(), e2.max());
+//    }
+//
+//    public static boolean overlap(double[] min, double[] max, double[] min2, double[] max2) {
+//        for (int d = 0; d < min.length; d++) {
+//            if (max[d] < min2[d] || min[d] > max2[d]) {
+//                return false;
+//            }
+//        }
+//        return true;
+//    }
+
+    public static boolean overlap(double[] min, double[] max, double[] center, double radius) {
+        for (int d = 0; d < min.length; d++) {
+            if (max[d] < center[d] - radius || min[d] > center[d] + radius) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+//    public static boolean isRectEnclosed(double[] minEnclosed, double[] maxEnclosed, double[] minOuter, double[] maxOuter) {
+//        for (int d = 0; d < minOuter.length; d++) {
+//            if (maxOuter[d] < maxEnclosed[d] || minOuter[d] > minEnclosed[d]) {
+//                return false;
+//            }
+//        }
+//        return true;
+//    }
+//
+//    /**
+//     * The tests for inclusion with UPPER BOUNDARY EXCLUSIVE!
+//     * I.e. it firs only if maxEnclosed is SMALLER than (center + radius).
+//     */
+//    public static boolean fitsIntoNode(double[] minEnclosed, double[] maxEnclosed, double[] centerNode, double radiusNode) {
+//        double r2 = 0;
+//        for (int d = 0; d < centerNode.length; d++) {
+//            double r = centerNode[d] -
+//            r2
+//            if ((centerNode[d] + radiusNode) <= maxEnclosed[d] || (centerNode[d] - radiusNode) > minEnclosed[d]) {
+//                return false;
+//            }
+//        }
+//        return true;
+//    }
+
+    public static boolean isNodeEnclosed(double[] centerEnclosed, double radiusEnclosed, double[] centerOuter, double radiusOuter) {
+        return PointDistance.l2(centerEnclosed, centerOuter) + radiusEnclosed <= radiusOuter;
+    }
+
+    public static <T> double[][] orderCoordinates(ArrayList<Index.PointEntry<T>> points) {
+        if (points.isEmpty()) {
+            return new double[0][0];
+        }
+        int dim = points.get(0).point().length;
+        double[][] sorted = new double[dim][points.size()];
+        for (int i = 0; i < points.size(); i++) {
+            double[] v = points.get(i).point();
+            for (int d = 0; d < dim; d++) {
+                sorted[d][i] = v[d];
+            }
+        }
+        for (int d = 0; d < dim; d++) {
+            Arrays.sort(sorted[d]);
+        }
+        return sorted;
+    }
+
+    public static <T> double calcBoundingSphere(ArrayList<Index.PointEntry<T>> points, double[] center) {
+		PointDistance dist = PointDistance.L2;
+        // TODO alternative approach:
+        //  - use orderCoordinates -> avg min/max -> center point.
+        //  - Increase radius until all points are included.
+        //  -> Traverses all points 2 times. -> 1 x min/max calculation + 1x distance calculation
+
+        // Default approach: Ritter's bounding sphere Algorithm
+		//  - random point, then find furthest, then find furthest again -> center is halfway distance
+        //  - Traverse all points again to ensure they are all included
+		//    Adjust radius and center. -> Center is moved by half of radius adjustment
+		//    -> This covers the worst case where another extreme point is exactly on the other side of the center
+        //  -> traverse all points 3 times. -> 3 x distance calculation
+        double maxDist = -1;
+        int posMaxDist = 0;
+        // initial random point -> find furthest neighbor
+        double[] p0 = points.get(0).point();
+        for (int i = 1; i < points.size(); i++) {
+            double d = dist.dist(p0, points.get(i));
+            if (d > maxDist) {
+                maxDist = d;
+                posMaxDist = i;
+            }
+        }
+        double[] pFurthest0 = points.get(posMaxDist).point();
+
+        maxDist = -1;
+        for (int i = 0; i < points.size(); i++) {
+            double d = dist.dist(pFurthest0, points.get(i));
+            if (d > maxDist) {
+                maxDist = d;
+                posMaxDist = i;
+            }
+        }
+        double[] pFurthest1 = points.get(posMaxDist).point();
+		double radius = maxDist / 2.0;
+
+		// center
+        int dim = pFurthest0.length;
+        for (int d = 0; d < dim; d++) {
+            center[d] = (pFurthest0[d] + pFurthest1[d]) / 2.;
+        }
+
+		for (int i = 0; i < points.size(); i++) {
+			double d = dist.dist(center, points.get(i));
+			if (d > radius) {
+				radius = d;
+				// TODO adjust center, see https://www.researchgate.net/profile/Jack-Ritter/publication/242453691_An_Efficient_Bounding_Sphere/links/56e9d24e08ae95bddc2a2358/An-Efficient-Bounding-Sphere
+				// double delta = (d - radius) / 2.;
+				// radius += delta;
+			}
+		}
+		return radius;
+    }
+}