ST_CompactnessRatio.java

/**
 * H2GIS is a library that brings spatial support to the H2 Database Engine
 * <http://www.h2database.com>. H2GIS is developed by CNRS
 * <http://www.cnrs.fr/>.
 *
 * This code is part of the H2GIS project. H2GIS is free software; 
 * you can redistribute it and/or modify it under the terms of the GNU
 * Lesser General Public License as published by the Free Software Foundation;
 * version 3.0 of the License.
 *
 * H2GIS 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 Lesser General Public License
 * for more details <http://www.gnu.org/licenses/>.
 *
 *
 * For more information, please consult: <http://www.h2gis.org/>
 * or contact directly: info_at_h2gis.org
 */

package org.h2gis.functions.spatial.properties;

import com.vividsolutions.jts.geom.Geometry;
import com.vividsolutions.jts.geom.Polygon;
import org.h2gis.api.DeterministicScalarFunction;

/**
 * ST_CompactnessRatio computes the perimeter of a circle whose area is equal to the
 * given polygon's area, and returns the ratio of this computed perimeter to the given
 * polygon's perimeter.
 * <p/>
 * Equivalent definition: ST_CompactnessRatio returns the square root of the
 * polygon's area divided by the area of the circle with circumference equal to
 * the polygon's perimeter.
 * <p/>
 * Note: This uses the 2D perimeter/area of the polygon.
 *
 * @author Adam Gouge
 */
public class ST_CompactnessRatio extends DeterministicScalarFunction {

    public ST_CompactnessRatio() {
        addProperty(PROP_REMARKS, "Returns the compactness ratio of the " +
                "given polygon, defined to be the the perimeter of a circle " +
                "whose area is equal to the given geometry's area divided by " +
                "the given polygon's perimeter.");
    }

    @Override
    public String getJavaStaticMethod() {
        return "computeCompacity";
    }

    /**
     * Returns the compactness ratio of the given polygon
     *
     * @param geom Geometry
     * @return The compactness ratio of the given polygon
     */
    public static Double computeCompacity(Geometry geom) {
        if(geom == null){
            return null;
        }
        if (geom instanceof Polygon) {
            final double circleRadius = Math.sqrt(geom.getArea() / Math.PI);
            final double circleCurcumference = 2 * Math.PI * circleRadius;
            return circleCurcumference / geom.getLength();
        }
        return null;
    }
}