EnvelopeUtil.java

/*
 * The Unified Mapping Platform (JUMP) is an extensible, interactive GUI 
 * for visualizing and manipulating spatial features with geometry and attributes.
 *
 * Copyright (C) 2003 Vivid Solutions
 * 
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
 * 
 * For more information, contact:
 *
 * Vivid Solutions
 * Suite #1A
 * 2328 Government Street
 * Victoria BC  V8T 5G5
 * Canada
 *
 * (250)385-6040
 * www.vividsolutions.com
 */

package com.vividsolutions.jump.geom;

import com.vividsolutions.jts.geom.*;
import com.vividsolutions.jump.util.MathUtil;


/**
 * Utility functions for {@link Envelope}s.
 */
public class EnvelopeUtil {
    private static GeometryFactory factory = new GeometryFactory();

    /**
     *  Expands an Envelope by a given distance.
     * Both positive and negative distances are handled.
     */
    public static Envelope expand(Envelope env, double distance) {
        /**
         *  If creating a negative buffer, check if Envelope becomes null (0-size)
         */
        if (distance < 0) {
            double minSize = 2.0 * -distance;

            if (env.getWidth() < minSize) {
                return new Envelope();
            }

            if (env.getHeight() < minSize) {
                return new Envelope();
            }
        }

        return new Envelope(env.getMinX() - distance, env.getMaxX() + distance,
            env.getMinY() - distance, env.getMaxY() + distance);
    }

    public static void translate(Envelope e, Coordinate displacement) {
        if (e.isNull()) {
            return;
        }

        e.init(e.getMinX() + displacement.x, e.getMaxX() + displacement.x,
            e.getMinY() + displacement.y, e.getMaxY() + displacement.y);
    }

    /**
     * @param originalEnvelope the original envelope
     * @param extentFraction the buffer distance expressed as a fraction of the
     * average envelope extent
     */
    public static Envelope bufferByFraction(Envelope originalEnvelope,
        double extentFraction) {
        Envelope bufferedEnvelope = new Envelope(originalEnvelope);
        double averageExtent = (bufferedEnvelope.getWidth() +
            bufferedEnvelope.getHeight()) / 2d;
        double buffer = averageExtent * extentFraction;

        if (averageExtent == 0) {
            //Point feature. Set the buffer to something reasonable. [Jon Aquino]
            buffer = 10;
        }

        bufferedEnvelope.expandToInclude(bufferedEnvelope.getMaxX() + buffer,
            bufferedEnvelope.getMaxY() + buffer);
        bufferedEnvelope.expandToInclude(bufferedEnvelope.getMinX() - buffer,
            bufferedEnvelope.getMinY() - buffer);

        return bufferedEnvelope;
    }

    public static Coordinate centre(Envelope e) {
        return new Coordinate(MathUtil.avg(e.getMinX(), e.getMaxX()),
            MathUtil.avg(e.getMinY(), e.getMaxY()));
    }

    public static Geometry toGeometry(Envelope envelope) {
        if ((envelope.getWidth() == 0) && (envelope.getHeight() == 0)) {
            return factory.createPoint(new Coordinate(envelope.getMinX(),
                    envelope.getMinY()));
        }

        if ((envelope.getWidth() == 0) || (envelope.getHeight() == 0)) {
            return factory.createLineString(new Coordinate[] {
                    new Coordinate(envelope.getMinX(), envelope.getMinY()),
                    new Coordinate(envelope.getMaxX(), envelope.getMaxY())
                });
        }

        return factory.createPolygon(factory.createLinearRing(
                new Coordinate[] {
                    new Coordinate(envelope.getMinX(), envelope.getMinY()),
                    new Coordinate(envelope.getMinX(), envelope.getMaxY()),
                    new Coordinate(envelope.getMaxX(), envelope.getMaxY()),
                    new Coordinate(envelope.getMaxX(), envelope.getMinY()),
                    new Coordinate(envelope.getMinX(), envelope.getMinY())
                }), null);
    }
}