/*
* GeoTools - The Open Source Java GIS Toolkit
* http://geotools.org
*
* (C) 2011, Open Source Geospatial Foundation (OSGeo)
* (C) 2003-2005, Open Geospatial Consortium Inc.
*
* All Rights Reserved. http://www.opengis.org/legal/
*/
package org.opengis.referencing.datum;
import javax.measure.unit.Unit;
import javax.measure.quantity.Length;
import org.opengis.referencing.IdentifiedObject;
import org.opengis.annotation.UML;
import static org.opengis.annotation.Obligation.*;
import static org.opengis.annotation.Specification.*;
/**
* Geometric figure that can be used to describe the approximate shape of the earth.
* In mathematical terms, it is a surface formed by the rotation of an ellipse about
* its minor axis. An ellipsoid requires two defining parameters:
* <p>
* <ul>
* <li>{@linkplain #getSemiMajorAxis semi-major axis} and
* {@linkplain #getInverseFlattening inverse flattening}, or</li>
* <li>{@linkplain #getSemiMajorAxis semi-major axis} and
* {@linkplain #getSemiMinorAxis semi-minor axis}.</li>
* </ul>
* <p>
* There is not just one ellipsoid. An ellipsoid is a matter of choice, and therefore many
* choices are possible. The size and shape of an ellipsoid was traditionally chosen such
* that the surface of the geoid is matched as closely as possible locally, e.g. in a country.
* A number of global best-fit ellipsoids are now available. An association of an ellipsoid with
* the earth is made through the definition of the size and shape of the ellipsoid and the position
* and orientation of this ellipsoid with respect to the earth. Collectively this choice is captured
* by the concept of "{@linkplain GeodeticDatum geodetic datum}". A change of size, shape, position
* or orientation of an ellipsoid will result in a change of geographic coordinates of a point and
* be described as a different geodetic datum. Conversely geographic coordinates are unambiguous
* only when associated with a geodetic datum.
*
* @departure
* ISO 19111 defines {@link #getSemiMinorAxis semiMinorAxis}, {@link #getInverseFlattening
* inverseFlattening} and {@link #isIvfDefinitive isSphere} in a separated structure named
* {@code secondDefiningParameter} of type {@code union}. The C/C++ concept of {@code union}
* doesn't exist in Java, but implementors can achieve the same functionality by providing
* different {@code Ellipsoid} subclasses computing one parameter on-the-fly from the other
* one. The {@link #isIvfDefinitive isIvfDefinitive} attribute imported from OGC 01-004 can
* be used for distinguishing between the two cases.
*
*
* @source $URL: http://svn.osgeo.org/geotools/branches/2.7.x/modules/library/opengis/src/main/java/org/opengis/referencing/datum/Ellipsoid.java $
* @version <A HREF="http://portal.opengeospatial.org/files/?artifact_id=6716">Abstract specification 2.0</A>
* @author Martin Desruisseaux (IRD)
* @since GeoAPI 1.0
*/
@UML(identifier="CD_Ellipsoid", specification=ISO_19111)
public interface Ellipsoid extends IdentifiedObject {
/**
* Returns the linear unit of the {@linkplain #getSemiMajorAxis semi-major}
* and {@linkplain #getSemiMinorAxis semi-minor} axis values.
*
* @return The axis linear unit.
*/
@UML(identifier="getAxisUnit", specification=OGC_01009)
Unit<Length> getAxisUnit();
/**
* Length of the semi-major axis of the ellipsoid. This is the
* equatorial radius in {@linkplain #getAxisUnit axis linear unit}.
*
* @return Length of semi-major axis.
* @unitof Length
*/
@UML(identifier="semiMajorAxis", obligation=MANDATORY, specification=ISO_19111)
double getSemiMajorAxis();
/**
* Length of the semi-minor axis of the ellipsoid. This is the
* polar radius in {@linkplain #getAxisUnit axis linear unit}.
*
* @return Length of semi-minor axis.
* @unitof Length
*/
@UML(identifier="secondDefiningParameter.semiMinorAxis", obligation=CONDITIONAL, specification=ISO_19111)
double getSemiMinorAxis();
/**
* Returns the value of the inverse of the flattening constant. The inverse
* flattening is related to the equatorial/polar radius by the formula
*
* <var>ivf</var> = <var>r</var><sub>e</sub>/(<var>r</var><sub>e</sub>-<var>r</var><sub>p</sub>).
*
* For perfect spheres (i.e. if {@link #isSphere} returns {@code true}),
* the {@link Double#POSITIVE_INFINITY POSITIVE_INFINITY} value is used.
*
* @return The inverse flattening value.
* @unitof Scale
*/
@UML(identifier="secondDefiningParameter.inverseFlattening", obligation=CONDITIONAL, specification=ISO_19111)
double getInverseFlattening();
/**
* Indicates if the {@linkplain #getInverseFlattening inverse flattening} is definitive for
* this ellipsoid. Some ellipsoids use the IVF as the defining value, and calculate the polar
* radius whenever asked. Other ellipsoids use the polar radius to calculate the IVF whenever
* asked. This distinction can be important to avoid floating-point rounding errors.
*
* @return {@code true} if the {@linkplain #getInverseFlattening inverse flattening} is
* definitive, or {@code false} if the {@linkplain #getSemiMinorAxis polar radius}
* is definitive.
*/
@UML(identifier="CS_Ellipsoid.isIvfDefinitive", obligation=CONDITIONAL, specification=OGC_01009)
boolean isIvfDefinitive();
/**
* {@code true} if the ellipsoid is degenerate and is actually a sphere. The sphere is
* completely defined by the {@linkplain #getSemiMajorAxis semi-major axis}, which is the
* radius of the sphere.
*
* @return {@code true} if the ellipsoid is degenerate and is actually a sphere.
*/
@UML(identifier="secondDefiningParameter.isSphere", obligation=CONDITIONAL, specification=ISO_19111)
boolean isSphere();
}