/*
* Copyright (c) 2016 Vivid Solutions.
*
* All rights reserved. This program and the accompanying materials
* are made available under the terms of the Eclipse Public License v1.0
* and Eclipse Distribution License v. 1.0 which accompanies this distribution.
* The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
* and the Eclipse Distribution License is available at
*
* http://www.eclipse.org/org/documents/edl-v10.php.
*/
package org.locationtech.jtsexample.technique;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import org.locationtech.jts.geom.*;
import org.locationtech.jts.geom.prep.*;
import org.locationtech.jts.index.SpatialIndex;
import org.locationtech.jts.index.strtree.STRtree;
import org.locationtech.jts.util.Stopwatch;
/**
* Demonstrates use of {@link PreparedGeometry}s in a spatial index
* to optimize spatial search.
*
* The example creates a grid of circular polygons, packed into the 1 x 1 square.
* This set of polygons is spatially indexed as PreparedGeometrys in an STRtree index.
* A series of random points in the square is generated, and the index
* is used to determine whether each point intersects any circles.
* The fraction of points which intersect will approximate the
* fraction of area covered by the circles.
*
* @version 1.12
*/
public class SearchUsingPreparedGeometryIndex
{
static GeometryFactory geomFact = new GeometryFactory();
static final int MAX_ITER = 200000;
static final int GRID_SIZE = 10;
static final int POLYGON_SIZE = 100;
public static void main(String[] args)
throws Exception
{
List circleGrid = createCircleGrid(GRID_SIZE);
PreparedGeometryIndex pgIndex = new PreparedGeometryIndex();
pgIndex.insert(circleGrid);
Stopwatch sw = new Stopwatch();
int inCount = runIndexedQuery(pgIndex);
String indexTime = sw.getTimeString();
System.out.println("Number of iterations = " + MAX_ITER );
System.out.println("Number of circles in grid = " + circleGrid.size() );
System.out.println();
System.out.println("The fraction of intersecting points should approximate the total area of the circles:");
System.out.println();
System.out.println("Area of circles = " + area(circleGrid) );
System.out.println("Fraction of points in circles = " + inCount / (double) MAX_ITER );
System.out.println();
System.out.println("Indexed Execution time: " + indexTime );
/**
* For comparison purposes run the same query without using an index
*/
Stopwatch sw2 = new Stopwatch();
int inCount2 = runBruteForceQuery(circleGrid);
String bruteForceTime = sw2.getTimeString();
System.out.println();
System.out.println("Execution time: " + bruteForceTime );
}
static int runIndexedQuery(PreparedGeometryIndex pgIndex)
{
int inCount = 0;
for (int i = 0; i < MAX_ITER; i++)
{
Point randPt = createRandomPoint();
if (pgIndex.intersects(randPt).size() > 0) {
inCount++;
}
}
return inCount;
}
static int runBruteForceQuery(Collection geoms)
{
int inCount = 0;
for (int i = 0; i < MAX_ITER; i++)
{
Point randPt = createRandomPoint();
if (findIntersecting(geoms, randPt).size() > 0) {
inCount++;
}
}
return inCount;
}
static double area(Collection geoms)
{
double area = 0.0;
for (Iterator i = geoms.iterator(); i.hasNext(); ) {
Geometry geom = (Geometry) i.next();
area += geom.getArea();
}
return area;
}
static List createCircleGrid(int gridSize)
{
double diameter = 1.0 / gridSize;
double radius = diameter / 2;
List circles = new ArrayList();
for (int i = 0; i < gridSize; i++) {
for (int j = 0; j < gridSize; j++) {
Coordinate centre = new Coordinate(radius + i * diameter, radius + j * diameter);
Geometry circle = createCircle(centre, radius);
circles.add(circle);
}
}
return circles;
}
static Geometry createCircle(Coordinate centre, double radius)
{
Geometry centrePt = geomFact.createPoint(centre);
return centrePt.buffer(radius, POLYGON_SIZE);
}
static Point createRandomPoint()
{
return geomFact.createPoint(new Coordinate(Math.random(), Math.random()));
}
static List findIntersecting(Collection targetGeoms, Geometry queryGeom)
{
List result = new ArrayList();
for (Iterator it = targetGeoms.iterator(); it.hasNext(); ) {
Geometry test = (Geometry) it.next();
if (test.intersects(queryGeom)) {
result.add(test);
}
}
return result;
}
}
/**
* A spatial index which indexes {@link PreparedGeometry}s
* created from a set of {@link Geometry}s.
* This can be used for efficient testing
* for intersection with a series of target geomtries.
*
* @author Martin Davis
*
*/
class PreparedGeometryIndex
{
private SpatialIndex index = new STRtree();
/**
* Creates a new index
*
*/
public PreparedGeometryIndex()
{
}
/**
* Inserts a collection of Geometrys into the index.
*
* @param geoms a collection of Geometrys to insert
*/
public void insert(Collection geoms)
{
for (Iterator i = geoms.iterator(); i.hasNext(); ) {
Geometry geom = (Geometry) i.next();
index.insert(geom.getEnvelopeInternal(), PreparedGeometryFactory.prepare(geom));
}
}
/**
* Finds all {@link PreparedGeometry}s which might
* interact with a query {@link Geometry}.
*
* @param g the geometry to query by
* @return a list of candidate PreparedGeometrys
*/
public List query(Geometry g)
{
return index.query(g.getEnvelopeInternal());
}
/**
* Finds all {@link PreparedGeometry}s which intersect a given {@link Geometry}
*
* @param g the geometry to query by
* @return a list of intersecting PreparedGeometrys
*/
public List intersects(Geometry g)
{
List result = new ArrayList();
List candidates = query(g);
for (Iterator it = candidates.iterator(); it.hasNext(); ) {
PreparedGeometry prepGeom = (PreparedGeometry) it.next();
if (prepGeom.intersects(g)) {
result.add(prepGeom);
}
}
return result;
}
}