package com.vividsolutions.jts.operation.distance;
import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.Lineal;
import com.vividsolutions.jts.geom.Polygonal;
import com.vividsolutions.jts.geom.Puntal;
import com.vividsolutions.jts.index.strtree.ItemBoundable;
import com.vividsolutions.jts.index.strtree.ItemDistance;
import com.vividsolutions.jts.index.strtree.STRtree;
/**
* Computes the distance between the facets (segments and vertices)
* of two {@link Geometry}s
* using a Branch-and-Bound algorithm.
* The Branch-and-Bound algorithm operates over a
* traversal of R-trees built
* on the target and possibly also the query geometries.
* <p>
* This approach provides the following benefits:
* <ul>
* <li>Performance is improved due to the effects of the
* R-tree index
* and the pruning due to the Branch-and-Bound approach
* <li>The spatial index on the target geometry can be cached
* to allow reuse in an incremental query situation.
* </ul>
* Using this technique can be much more performant
* than using {@link #getDistance(Geometry)}
* when one or both
* input geometries are large,
* or when evaluating many distance computations against
* a single geometry.
* <p>
* This class is not thread-safe.
*
* @author Martin Davis
*
*/
public class IndexedFacetDistance
{
/**
* Computes the distance between two geometries using
* the indexed approach.
* <p>
* For geometries with many segments or points,
* this can be faster than using a simple distance
* algorithm.
*
* @param g1 a geometry
* @param g2 a geometry
* @return the distance between the two geometries
*/
public static double distance(Geometry g1, Geometry g2)
{
IndexedFacetDistance dist = new IndexedFacetDistance(g1);
return dist.getDistance(g2);
}
private STRtree cachedTree;
/**
* Creates a new distance-finding instance for a given target {@link Geometry}.
* <p>
* Distances will be computed to all facets of the input geometry.
* The facets of the geometry are the discrete segments and points
* contained in its components.
* In the case of {@link Lineal} and {@link Puntal} inputs,
* this is equivalent to computing the conventional distance.
* In the case of {@link Polygonal} inputs, this is equivalent
* to computing the distance to the polygons boundaries.
*
* @param g1 a Geometry, which may be of any type.
*/
public IndexedFacetDistance(Geometry g1) {
cachedTree = FacetSequenceTreeBuilder.build(g1);
}
/**
* Computes the distance from the base geometry to
* the given geometry.
*
* @param g the geometry to compute the distance to
*
* @return the computed distance
*/
public double getDistance(Geometry g)
{
STRtree tree2 = FacetSequenceTreeBuilder.build(g);
Object[] obj = cachedTree.nearestNeighbour(tree2,
new FacetSequenceDistance());
return facetDistance(obj);
}
private static double facetDistance(Object[] obj)
{
Object o1 = obj[0];
Object o2 = obj[1];
return ((FacetSequence) o1).distance((FacetSequence) o2);
}
/**
* Computes the distance from the base geometry to
* the given geometry, up to and including a given
* maximum distance.
*
* @param g the geometry to compute the distance to
* @param maximumDistance the maximum distance to compute.
*
* @return the computed distance,
* or <tt>maximumDistance</tt> if the true distance is determined to be greater
*/
// TODO: implement this
/*
public double getDistanceWithin(Geometry g, double maximumDistance)
{
STRtree tree2 = FacetSequenceTreeBuilder.build(g);
Object[] obj = cachedTree.nearestNeighbours(tree2,
new FacetSequenceDistance());
return facetDistance(obj);
}
*/
/**
* Tests whether the base geometry lies within
* a specified distance of the given geometry.
*
* @param g the geomtry to test
* @param maximumDistance the maximum distance to test
* @return true if the geometry lies with the specified distance
*/
// TODO: implement this
/*
public boolean isWithinDistance(Geometry g, double maximumDistance)
{
STRtree tree2 = FacetSequenceTreeBuilder.build(g);
double dist = findMinDistance(cachedTree.getRoot(), tree2.getRoot(), maximumDistance);
if (dist <= maximumDistance)
return false;
return true;
}
*/
private static class FacetSequenceDistance
implements ItemDistance
{
public double distance(ItemBoundable item1, ItemBoundable item2) {
FacetSequence fs1 = (FacetSequence) item1.getItem();
FacetSequence fs2 = (FacetSequence) item2.getItem();
return fs1.distance(fs2);
}
}
}