Cell.java

package au.gov.amsa.geo.model;

import java.io.Serializable;

import au.gov.amsa.risky.format.HasPosition;

import com.google.common.base.Optional;

/**
 * A latitude longitude rectangle bordered by rhumb lines east-west and
 * north-south. The rectangle is equal in degrees in width and height (but in
 * terms of distance this can of course vary depending on the location of the
 * cell on the earth).
 */
public class Cell implements Serializable {

    private static final long serialVersionUID = 5489135874617545438L;
    private static final double radiusEarthKm = 6371.01;
    private static final double KM_PER_NM = 1.852;

    private final long latIndex;
    private final long lonIndex;
    private final int hashCode;

    /**
     * Constructor.
     * 
     * @param latIndex
     * @param lonIndex
     */
    Cell(long latIndex, long lonIndex) {
        this.latIndex = latIndex;
        this.lonIndex = lonIndex;
        hashCode = calculateHashCode();
    }

    public static Optional<Cell> cellAt(HasPosition p, Options options) {
        return cellAt(p.lat(), p.lon(), options);
    }

    public static Optional<Cell> cellAt(double lat, double lon, Options options) {
        return options.getGrid().cellAt(lat, lon);
    }

    public double leftEdgeLongitude(Options options) {
        return options.getGrid().leftEdgeLongitude(this);
    }

    public double rightEdgeLongitude(Options options) {
        return options.getGrid().rightEdgeLongitude(this);
    }

    public double topEdgeLatitude(Options options) {
        return options.getGrid().topEdgeLatitude(this);
    }

    public double bottomEdgeLatitude(Options options) {
        return options.getGrid().bottomEdgeLatitude(this);
    }

    public long getLatIndex() {
        return latIndex;
    }

    public long getLonIndex() {
        return lonIndex;
    }

    public double getCentreLon(Options options) {
        return options.getGrid().centreLon(lonIndex);
    }

    public double getCentreLat(Options options) {
        return options.getGrid().centreLat(latIndex);
    }

    /**
     * From http://mathforum.org/library/drmath/view/63767.html
     * 
     * @param options
     * @return
     */
    public double areaNauticalMiles(Options options) {
        double topLatRads = Math.toRadians(topEdgeLatitude(options));
        double bottomLatRads = Math.toRadians(bottomEdgeLatitude(options));

        return Math.PI / 180 * radiusEarthKm * radiusEarthKm
                * Math.abs(Math.sin(topLatRads) - Math.sin(bottomLatRads))
                * options.getCellSizeDegreesAsDouble() / (KM_PER_NM * KM_PER_NM);
    }

    @Override
    public int hashCode() {
        return hashCode;
    }

    private int calculateHashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + (int) (latIndex ^ (latIndex >>> 32));
        result = prime * result + (int) (lonIndex ^ (lonIndex >>> 32));
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Cell other = (Cell) obj;
        if (latIndex != other.latIndex)
            return false;
        if (lonIndex != other.lonIndex)
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "Cell [latIndex=" + latIndex + ", lonIndex=" + lonIndex + "]";
    }

}