Package org.geotools.api.referencing.datum

Interface Ellipsoid

  • All Superinterfaces:
    IdentifiedObject
    All Known Implementing Classes:
    DefaultEllipsoid
    public interface Ellipsoid
extends IdentifiedObject
    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:

    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 "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.

    Since:
    GeoAPI 1.0
    Author:
    Martin Desruisseaux (IRD)

    • Method Detail

      • getAxisUnit

        Unit<Length> getAxisUnit()
        Returns the linear unit of the semi-major and semi-minor axis values.
        Returns:
        The axis linear unit.

      • getSemiMajorAxis

        double getSemiMajorAxis()
        Length of the semi-major axis of the ellipsoid. This is the equatorial radius in axis linear unit.
        Returns:
        Length of semi-major axis.

      • getInverseFlattening

        @UML(identifier="secondDefiningParameter.inverseFlattening",
     obligation=CONDITIONAL,
     specification=ISO_19111)
double getInverseFlattening()
        Returns the value of the inverse of the flattening constant. The inverse flattening is related to the equatorial/polar radius by the formula

        ivf = re/(re-rp).

        For perfect spheres (i.e. if isSphere() returns true), the POSITIVE_INFINITY value is used.

        Returns:
        The inverse flattening value.

      • isIvfDefinitive

        @UML(identifier="CS_Ellipsoid.isIvfDefinitive",
     obligation=CONDITIONAL,
     specification=OGC_01009)
boolean isIvfDefinitive()
        Indicates if the 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.
        Returns:
        true if the inverse flattening is definitive, or false if the polar radius is definitive.