ADD: node to node distance

src/mhtree/BuildTree.java

@@ -6,6 +6,7 @@ import messif.buckets.BucketStorageException;
 import messif.objects.LocalAbstractObject;
 
 import java.util.*;
+import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 import java.util.stream.IntStream;
@@ -24,16 +25,21 @@ class BuildTree {
     private final InsertType insertType;
     private final ObjectToNodeDistance objectToNodeDistance;
     private final BucketDispatcher bucketDispatcher;
+    private final BiFunction<Float, Float, Float> distanceSelector;
 
     private Node root;
 
-    BuildTree(List<LocalAbstractObject> objects, int leafCapacity, int arity, InsertType insertType, ObjectToNodeDistance objectToNodeDistance, BucketDispatcher bucketDispatcher) throws BucketStorageException {
+    BuildTree(List<LocalAbstractObject> objects, int leafCapacity, int arity, InsertType insertType, ObjectToNodeDistance objectToNodeDistance, NodeToNodeDistance nodeToNodeDistance, BucketDispatcher bucketDispatcher) throws BucketStorageException {
         this.arity = arity;
         this.leafCapacity = leafCapacity;
         this.insertType = insertType;
         this.objectToNodeDistance = objectToNodeDistance;
         this.bucketDispatcher = bucketDispatcher;
 
+        // Set distance selector function for two hull objects
+        boolean selectNearest = nodeToNodeDistance == NodeToNodeDistance.NEAREST_HULL_OBJECTS;
+        distanceSelector = selectNearest ? Math::min : Math::max;
+
         nodes = new Node[objects.size() / leafCapacity];
 
         validNodeIndices = new BitSet(nodes.length);
@@ -50,7 +56,7 @@ class BuildTree {
 
         createLeafNodes();
 
-        precomputeNodeDistances();
+        precomputeLeafNodeDistances();
 
         buildTree();
     }
@@ -175,20 +181,20 @@ class BuildTree {
         }).collect(Collectors.toSet());
     }
 
-    private void precomputeNodeDistances() {
+    private void precomputeLeafNodeDistances() {
         for (int i = 0; i < nodes.length; i++) {
             for (int j = i + 1; j < nodes.length; j++) {
-                float minDistance = Float.MAX_VALUE;
+                float distance = Float.MAX_VALUE;
 
-                for (LocalAbstractObject firstPoint : nodes[i].getObjects())
-                    for (LocalAbstractObject secondPoint : nodes[j].getObjects())
-                        minDistance = Math.min(minDistance, objectDistances.getDistance(firstPoint, secondPoint));
+                for (LocalAbstractObject firstHullObject : nodes[i].getHullObjects())
+                    for (LocalAbstractObject secondHullObject : nodes[j].getHullObjects())
+                        distance = distanceSelector.apply(distance, objectDistances.getDistance(firstHullObject, secondHullObject));
 
-                if (minDistance == 0f)
+                if (distance == 0f)
                     throw new RuntimeException("Zero distance between " + nodes[i].toString() + " and " + nodes[j].toString());
 
-                nodeDistances[i][j] = minDistance;
-                nodeDistances[j][i] = minDistance;
+                nodeDistances[i][j] = distance;
+                nodeDistances[j][i] = distance;
             }
         }
     }
@@ -219,13 +225,13 @@ class BuildTree {
         if (nodeIndices.size() == 0) return;
 
         validNodeIndices.stream().forEach(i -> {
-            float minDistance = nodeDistances[baseNodeIndex][i];
+            float distance = nodeDistances[baseNodeIndex][i];
 
             for (int index : nodeIndices)
-                minDistance = Math.min(minDistance, nodeDistances[index][i]);
+                distance = distanceSelector.apply(distance, nodeDistances[index][i]);
 
-            nodeDistances[baseNodeIndex][i] = minDistance;
-            nodeDistances[i][baseNodeIndex] = minDistance;
+            nodeDistances[baseNodeIndex][i] = distance;
+            nodeDistances[i][baseNodeIndex] = distance;
         });
     }
 }

src/mhtree/MHTree.java

@@ -29,6 +29,7 @@ public class MHTree extends Algorithm implements Serializable {
     private final BucketDispatcher bucketDispatcher;
     private final InsertType insertType;
     private final ObjectToNodeDistance objectToNodeDistance;
+    private final NodeToNodeDistance nodeToNodeDistance;
 
     private final StatisticCounter statVisitedLeaves = StatisticCounter.getStatistics("Node.Leaf.Visited");
 
@@ -42,17 +43,18 @@ public class MHTree extends Algorithm implements Serializable {
             "storage class for buckets",
             "storage class parameters"
     })
-    public MHTree(List<LocalAbstractObject> objects, int leafCapacity, int arity, InsertType insertType, ObjectToNodeDistance objectToNodeDistance, Class<? extends LocalBucket> defaultBucketClass, Map<String, Object> bucketClassParams) throws BucketStorageException {
+    public MHTree(List<LocalAbstractObject> objects, int leafCapacity, int arity, InsertType insertType, ObjectToNodeDistance objectToNodeDistance, NodeToNodeDistance nodeToNodeDistance, Class<? extends LocalBucket> defaultBucketClass, Map<String, Object> bucketClassParams) throws BucketStorageException {
         super("MH-Tree");
 
         this.leafCapacity = leafCapacity;
         this.arity = arity;
         this.insertType = insertType;
         this.objectToNodeDistance = objectToNodeDistance;
+        this.nodeToNodeDistance = nodeToNodeDistance;
 
         bucketDispatcher = new BucketDispatcher(Integer.MAX_VALUE, Long.MAX_VALUE, leafCapacity, 0, false, defaultBucketClass, bucketClassParams);
 
-        root = new BuildTree(objects, leafCapacity, arity, insertType, objectToNodeDistance, bucketDispatcher).getRoot();
+        root = new BuildTree(objects, leafCapacity, arity, insertType, objectToNodeDistance, nodeToNodeDistance, bucketDispatcher).getRoot();
     }
 
     public void approxKNN(ApproxKNNQueryOperation operation, double coefficient) {
@@ -175,6 +177,7 @@ public class MHTree extends Algorithm implements Serializable {
                 ", root=" + root +
                 ", insertType" + insertType +
                 ", objectToNodeDistance" + objectToNodeDistance +
+                ", nodeToNodeDistance" + nodeToNodeDistance +
                 '}';
     }
 }

src/mhtree/NodeToNodeDistance.java

+package mhtree;
+
+public enum NodeToNodeDistance {
+    NEAREST_HULL_OBJECTS,
+    FURTHEST_HULL_OBJECTS,
+}