https://lucene.apache.org/lucene-parent/lucene-spatial-extras: Advanced Spatial Shape Strategies for Apache Lucene (The Apache Software Foundation) 
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 *     http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.lucene.spatial.vector;

import java.io.IOException;
import java.util.Objects;

import org.apache.lucene.document.DoubleDocValuesField;
import org.apache.lucene.document.DoublePoint;
import org.apache.lucene.document.Field;
import org.apache.lucene.document.FieldType;
import org.apache.lucene.document.StoredField;
import org.apache.lucene.index.DocValuesType;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.LeafReaderContext;
import org.apache.lucene.search.BooleanClause;
import org.apache.lucene.search.BooleanQuery;
import org.apache.lucene.search.ConstantScoreQuery;
import org.apache.lucene.search.ConstantScoreScorer;
import org.apache.lucene.search.ConstantScoreWeight;
import org.apache.lucene.search.DocIdSetIterator;
import org.apache.lucene.search.DoubleValues;
import org.apache.lucene.search.DoubleValuesSource;
import org.apache.lucene.search.IndexSearcher;
import org.apache.lucene.search.Query;
import org.apache.lucene.search.QueryVisitor;
import org.apache.lucene.search.ScoreMode;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.TwoPhaseIterator;
import org.apache.lucene.search.Weight;
import org.apache.lucene.spatial.SpatialStrategy;
import org.apache.lucene.spatial.query.SpatialArgs;
import org.apache.lucene.spatial.query.SpatialOperation;
import org.apache.lucene.spatial.query.UnsupportedSpatialOperation;
import org.locationtech.spatial4j.context.SpatialContext;
import org.locationtech.spatial4j.shape.Circle;
import org.locationtech.spatial4j.shape.Point;
import org.locationtech.spatial4j.shape.Rectangle;
import org.locationtech.spatial4j.shape.Shape;


Simple SpatialStrategy which represents Points in two numeric fields. The Strategy's best feature is decent distance sort. 

Characteristics:






Implementation:

 This is a simple Strategy. Search works with a pair of range queries on two DoublePoints representing x & y fields. A Circle query does the same bbox query but adds a ValueSource filter on SpatialStrategy.makeDistanceValueSource(Point). 

One performance shortcoming with this strategy is that a scenario involving
both a search using a Circle and sort will result in calculations for the
spatial distance being done twice -- once for the filter and second for the
sort.

@lucene.experimental
/**
 * Simple {@link SpatialStrategy} which represents Points in two numeric fields.
 * The Strategy's best feature is decent distance sort.
 *
 * <p>
 * <b>Characteristics:</b>
 * <br>
 * <ul>
 * <li>Only indexes points; just one per field value.</li>
 * <li>Can query by a rectangle or circle.</li>
 * <li>{@link
 * org.apache.lucene.spatial.query.SpatialOperation#Intersects} and {@link
 * SpatialOperation#IsWithin} is supported.</li>
 * <li>Requires DocValues for
 * {@link #makeDistanceValueSource(org.locationtech.spatial4j.shape.Point)} and for
 * searching with a Circle.</li>
 * </ul>
 *
 * <p>
 * <b>Implementation:</b>
 * <p>
 * This is a simple Strategy.  Search works with a pair of range queries on two {@link DoublePoint}s representing
 * x &amp; y fields.  A Circle query does the same bbox query but adds a
 * ValueSource filter on
 * {@link #makeDistanceValueSource(org.locationtech.spatial4j.shape.Point)}.
 * <p>
 * One performance shortcoming with this strategy is that a scenario involving
 * both a search using a Circle and sort will result in calculations for the
 * spatial distance being done twice -- once for the filter and second for the
 * sort.
 *
 * @lucene.experimental
 */
public class PointVectorStrategy extends SpatialStrategy {

  // note: we use a FieldType to articulate the options we want on the field.  We don't use it as-is with a Field, we
  //  create more than one Field.

  
pointValues, docValues, and nothing else.

/**
   * pointValues, docValues, and nothing else.
   */
  public static FieldType DEFAULT_FIELDTYPE;

  static {
    // Default: pointValues + docValues
    FieldType type = new FieldType();
    type.setDimensions(1, Double.BYTES);//pointValues (assume Double)
    type.setDocValuesType(DocValuesType.NUMERIC);//docValues
    type.setStored(false);
    type.freeze();
    DEFAULT_FIELDTYPE = type;
  }

  public static final String SUFFIX_X = "__x";
  public static final String SUFFIX_Y = "__y";

  private final String fieldNameX;
  private final String fieldNameY;

  private final int fieldsLen;
  private final boolean hasStored;
  private final boolean hasDocVals;
  private final boolean hasPointVals;

  
Create a new PointVectorStrategy instance that uses DoublePoint and DoublePoint.newRangeQuery 
/**
   * Create a new {@link PointVectorStrategy} instance that uses {@link DoublePoint} and {@link DoublePoint#newRangeQuery}
   */
  public static PointVectorStrategy newInstance(SpatialContext ctx, String fieldNamePrefix) {
    return new PointVectorStrategy(ctx, fieldNamePrefix, DEFAULT_FIELDTYPE);
  }

  
Create a new instance configured with the provided FieldType options. See DEFAULT_FIELDTYPE. a field type is used to articulate the desired options (namely pointValues, docValues, stored). Legacy numerics is configurable this way too. 
/**
   * Create a new instance configured with the provided FieldType options. See {@link #DEFAULT_FIELDTYPE}.
   * a field type is used to articulate the desired options (namely pointValues, docValues, stored).  Legacy numerics
   * is configurable this way too.
   */
  public PointVectorStrategy(SpatialContext ctx, String fieldNamePrefix, FieldType fieldType) {
    super(ctx, fieldNamePrefix);
    this.fieldNameX = fieldNamePrefix+SUFFIX_X;
    this.fieldNameY = fieldNamePrefix+SUFFIX_Y;

    int numPairs = 0;
    if ((this.hasStored = fieldType.stored())) {
      numPairs++;
    }
    if ((this.hasDocVals = fieldType.docValuesType() != DocValuesType.NONE)) {
      numPairs++;
    }
    if ((this.hasPointVals = fieldType.pointDimensionCount() > 0)) {
      numPairs++;
    }
    this.fieldsLen = numPairs * 2;
  }


  String getFieldNameX() {
    return fieldNameX;
  }

  String getFieldNameY() {
    return fieldNameY;
  }

  @Override
  public Field[] createIndexableFields(Shape shape) {
    if (shape instanceof Point)
      return createIndexableFields((Point) shape);
    throw new UnsupportedOperationException("Can only index Point, not " + shape);
  }

  
See Also:
/** @see #createIndexableFields(org.locationtech.spatial4j.shape.Shape) */
  public Field[] createIndexableFields(Point point) {
    Field[] fields = new Field[fieldsLen];
    int idx = -1;
    if (hasStored) {
      fields[++idx] = new StoredField(fieldNameX, point.getX());
      fields[++idx] = new StoredField(fieldNameY, point.getY());
    }
    if (hasDocVals) {
      fields[++idx] = new DoubleDocValuesField(fieldNameX, point.getX());
      fields[++idx] = new DoubleDocValuesField(fieldNameY, point.getY());
    }
    if (hasPointVals) {
      fields[++idx] = new DoublePoint(fieldNameX, point.getX());
      fields[++idx] = new DoublePoint(fieldNameY, point.getY());
    }
    assert idx == fields.length - 1;
    return fields;
  }

  @Override
  public DoubleValuesSource makeDistanceValueSource(Point queryPoint, double multiplier) {
    return new DistanceValueSource(this, queryPoint, multiplier);
  }

  @Override
  public Query makeQuery(SpatialArgs args) {
    if(! SpatialOperation.is( args.getOperation(),
        SpatialOperation.Intersects,
        SpatialOperation.IsWithin ))
      throw new UnsupportedSpatialOperation(args.getOperation());
    Shape shape = args.getShape();
    if (shape instanceof Rectangle) {
      Rectangle bbox = (Rectangle) shape;
      return new ConstantScoreQuery(makeWithin(bbox));
    } else if (shape instanceof Circle) {
      Circle circle = (Circle)shape;
      Rectangle bbox = circle.getBoundingBox();
      return new DistanceRangeQuery(makeWithin(bbox), makeDistanceValueSource(circle.getCenter()), circle.getRadius());
    } else {
      throw new UnsupportedOperationException("Only Rectangles and Circles are currently supported, " +
          "found [" + shape.getClass() + "]");//TODO
    }
  }

  
Constructs a query to retrieve documents that fully contain the input envelope.

/**
   * Constructs a query to retrieve documents that fully contain the input envelope.
   */
  private Query makeWithin(Rectangle bbox) {
    BooleanQuery.Builder bq = new BooleanQuery.Builder();
    BooleanClause.Occur MUST = BooleanClause.Occur.MUST;
    if (bbox.getCrossesDateLine()) {
      //use null as performance trick since no data will be beyond the world bounds
      bq.add(rangeQuery(fieldNameX, null/*-180*/, bbox.getMaxX()), BooleanClause.Occur.SHOULD );
      bq.add(rangeQuery(fieldNameX, bbox.getMinX(), null/*+180*/), BooleanClause.Occur.SHOULD );
      bq.setMinimumNumberShouldMatch(1);//must match at least one of the SHOULD
    } else {
      bq.add(rangeQuery(fieldNameX, bbox.getMinX(), bbox.getMaxX()), MUST);
    }
    bq.add(rangeQuery(fieldNameY, bbox.getMinY(), bbox.getMaxY()), MUST);
    return bq.build();
  }

  
Returns a numeric range query based on FieldType DoublePoint.newRangeQuery is used for indexes created using DoublePoint fields 
/**
   * Returns a numeric range query based on FieldType
   * {@link DoublePoint#newRangeQuery} is used for indexes created using {@link DoublePoint} fields
   */
  private Query rangeQuery(String fieldName, Double min, Double max) {
    if (hasPointVals) {
      if (min == null) {
        min = Double.NEGATIVE_INFINITY;
      }

      if (max == null) {
        max = Double.POSITIVE_INFINITY;
      }

      return DoublePoint.newRangeQuery(fieldName, min, max);

    }
    //TODO try doc-value range query?
    throw new UnsupportedOperationException("An index is required for this operation.");
  }

  private static class DistanceRangeQuery extends Query {

    final Query inner;
    final DoubleValuesSource distanceSource;
    final double limit;

    private DistanceRangeQuery(Query inner, DoubleValuesSource distanceSource, double limit) {
      this.inner = inner;
      this.distanceSource = distanceSource;
      this.limit = limit;
    }

    @Override
    public Query rewrite(IndexReader reader) throws IOException {
      Query rewritten = inner.rewrite(reader);
      if (rewritten == inner)
        return this;
      return new DistanceRangeQuery(rewritten, distanceSource, limit);
    }

    @Override
    public void visit(QueryVisitor visitor) {
      visitor.visitLeaf(this);
    }

    @Override
    public Weight createWeight(IndexSearcher searcher, ScoreMode scoreMode, float boost) throws IOException {
      Weight w = inner.createWeight(searcher, scoreMode, 1f);
      return new ConstantScoreWeight(this, boost) {
        @Override
        public Scorer scorer(LeafReaderContext context) throws IOException {
          Scorer in = w.scorer(context);
          if (in == null)
            return null;
          DoubleValues v = distanceSource.getValues(context, DoubleValuesSource.fromScorer(in));
          DocIdSetIterator approximation = in.iterator();
          TwoPhaseIterator twoPhase = new TwoPhaseIterator(approximation) {
            @Override
            public boolean matches() throws IOException {
              return v.advanceExact(approximation.docID()) && v.doubleValue() <= limit;
            }

            @Override
            public float matchCost() {
              return 100;   // distance calculation can be heavy!
            }
          };
          return new ConstantScoreScorer(this, score(), scoreMode, twoPhase);
        }

        @Override
        public boolean isCacheable(LeafReaderContext ctx) {
          return distanceSource.isCacheable(ctx);
        }

      };
    }

    @Override
    public String toString(String field) {
      return "DistanceRangeQuery(" + inner.toString(field) + "; " + distanceSource.toString() + " < " + limit + ")";
    }

    @Override
    public boolean equals(Object o) {
      if (this == o) return true;
      if (o == null || getClass() != o.getClass()) return false;
      DistanceRangeQuery that = (DistanceRangeQuery) o;
      return Objects.equals(inner, that.inner) &&
          Objects.equals(distanceSource, that.distanceSource) && limit == that.limit;
    }

    @Override
    public int hashCode() {
      return Objects.hash(inner, distanceSource, limit);
    }
  }
}