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https://issues.apache.org/jira/browse/LUCENE-8126?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16320917#comment-16320917
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ASF GitHub Bot commented on LUCENE-8126:
----------------------------------------
Github user dsmiley commented on a diff in the pull request:
https://github.com/apache/lucene-solr/pull/302#discussion_r160773587
--- Diff:
lucene/spatial-extras/src/java/org/apache/lucene/spatial/prefix/tree/S2PrefixTree.java
---
@@ -0,0 +1,111 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.apache.lucene.spatial.prefix.tree;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.google.common.geometry.S2CellId;
+import com.google.common.geometry.S2LatLng;
+import com.google.common.geometry.S2Projections;
+import org.apache.lucene.util.BytesRef;
+import org.locationtech.spatial4j.context.SpatialContext;
+import org.locationtech.spatial4j.distance.DistanceUtils;
+import org.locationtech.spatial4j.shape.Point;
+import org.locationtech.spatial4j.shape.Shape;
+
+/**
+ * Spatial prefix tree for S2 Geometry. Shape factories for the given
{@link SpatialContext} must
+ * implement the interface {@link S2ShapeFactory}.
+ *
+ * @lucene.experimental
+ */
+public class S2PrefixTree extends SpatialPrefixTree {
+
+ /**
+ * Factory for creating {@link S2PrefixTree} instances with useful
defaults
+ */
+ public static class Factory extends SpatialPrefixTreeFactory {
+
+ @Override
+ protected int getLevelForDistance(double degrees) {
+ S2PrefixTree grid = new S2PrefixTree(ctx,
S2PrefixTree.MAX_LEVELS);
+ return grid.getLevelForDistance(degrees);
+ }
+
+ @Override
+ protected SpatialPrefixTree newSPT() {
+ return new S2PrefixTree(ctx,
+ maxLevels != null ? maxLevels : S2PrefixTree.MAX_LEVELS);
+ }
+ }
+
+ //factory to generate S2 cell shapes
+ protected final S2ShapeFactory s2ShapeFactory;
+ public static final int MAX_LEVELS = S2CellId.MAX_LEVEL + 1;
+
+ public S2PrefixTree(SpatialContext ctx, int maxLevels) {
+ super(ctx, maxLevels);
+ if (!(ctx.getShapeFactory() instanceof S2ShapeFactory)) {
+ throw new IllegalArgumentException("Spatial context does not
support S2 spatial index.");
+ }
+ this.s2ShapeFactory = (S2ShapeFactory) ctx.getShapeFactory();
+ }
+
+ @Override
+ public int getLevelForDistance(double dist) {
+ if (dist ==0){
+ return maxLevels;
+ }
+ return Math.min(maxLevels,
S2Projections.MAX_WIDTH.getClosestLevel(dist *
DistanceUtils.DEGREES_TO_RADIANS) +1);
+ }
+
+ @Override
+ public double getDistanceForLevel(int level) {
+ return S2Projections.MAX_WIDTH.getValue(level -1) *
DistanceUtils.RADIANS_TO_DEGREES;
+ }
+
+ @Override
+ public Cell getWorldCell() {
+ return new S2PrefixTreeCell(this, null);
+ }
+
+ @Override
+ public Cell readCell(BytesRef term, Cell scratch) {
+ S2PrefixTreeCell cell = (S2PrefixTreeCell) scratch;
+ if (cell == null)
+ cell = (S2PrefixTreeCell) getWorldCell();
+ cell.readCell(this, term);
+ return cell;
+ }
+
+ @Override
+ public CellIterator getTreeCellIterator(Shape shape, int detailLevel) {
+ if (!(shape instanceof Point)) {
+ return super.getTreeCellIterator(shape, detailLevel);
+ }
+ Point p = (Point) shape;
+ S2CellId id = S2CellId.fromLatLng(S2LatLng.fromDegrees(p.getY(),
p.getX())).parent(detailLevel-1);
+ List<Cell> cells = new ArrayList<>(detailLevel);
+ for (int i=0; i < detailLevel -1; i++) {
--- End diff --
nitpick: put a space after that minus operator
> Spatial prefix tree based on S2 geometry
> ----------------------------------------
>
> Key: LUCENE-8126
> URL: https://issues.apache.org/jira/browse/LUCENE-8126
> Project: Lucene - Core
> Issue Type: New Feature
> Components: modules/spatial-extras
> Reporter: Ignacio Vera
>
> Hi [~dsmiley],
> I have been working on a prefix tree based on goggle S2 geometry
> (https://s2geometry.io/) to be used mainly with Geo3d shapes with very
> promising results, in particular for complex shapes (e.g polygons). Using
> this pixelization scheme reduces the size of the index, improves the
> performance of the queries and reduces the loading time for non-point shapes.
> If you are ok with this contribution and before providing any code I would
> like to understand what is the correct/prefered approach:
> 1) Add new depency to the S2 library
> (https://mvnrepository.com/artifact/io.sgr/s2-geometry-library-java). It has
> Apache 2.0 license so it should be ok.
> 2) Create a utility class with all methods necessary to navigate the S2 tree
> and create shapes from S2 cells (basically port what we need from the library
> into Lucene).
> What do you think?
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