/*******************************************************************************
 * Copyright (c) 2013 The University of Reading
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University of Reading, nor the names of the
 *    authors or contributors may be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 ******************************************************************************/

package uk.ac.rdg.resc.edal.position;

import java.io.Serializable;

/**
 * <p>
 * A vertical coordinate reference system.
 * </p>
 * <p>
 * We don't use GeoAPI's VerticalCRS class here as we need to incorporate
 * pressure and dimensionless coordinates.
 * </p>
 * 
 * @author Guy Griffiths
 * @author Jon Blower
 */
public interface VerticalCrs extends Serializable {
    /**
     * Returns the units for the values in this {@link VerticalCrs}
     * <p>
     * TODO This may need replacing with a stronger type
     */
    public String getUnits();

    /**
     * Return true if this axis has units of pressure. If this is true then the
     * positive direction must be DOWN.
     */
    public boolean isPressure();

    /**
     * <p>
     * Return true if this is a dimensionless (e.g. sigma or terrain-following)
     * coordinate system. If this is true then the units are irrelevant, and
     * isPressure() will return false.
     * </p>
     * <p>
     * Future APIs will need to allow conversions between dimensionless and
     * dimensional coordinates, which will require more information. (The
     * conversion can be performed using existing routines, e.g. in
     * Java-NetCDF.) However, the current purpose of EDAL is not to perform the
     * conversion but to provide client code with enough information to decide
     * what to do.
     * </p>
     * 
     * @see <a
     *      href="http://cf-pcmdi.llnl.gov/documents/cf-conventions/1.5/cf-conventions.html#dimensionless-v-coord">CF
     *      conventions</a>
     */
    public boolean isDimensionless();

    /**
     * Indicates whether coordinate values increase upward or downward.
     */
    public boolean isPositiveUpwards();

    @Override
    public int hashCode();

    @Override
    public boolean equals(Object obj);
}
