Package org.apache.sis.referencing.datum

Class DefaultEllipsoid

java.lang.Object
org.apache.sis.io.wkt.FormattableObject
org.apache.sis.referencing.AbstractIdentifiedObject
org.apache.sis.referencing.datum.DefaultEllipsoid
All Implemented Interfaces:
Serializable, Formattable, Deprecable, LenientComparable, org.opengis.referencing.datum.Ellipsoid, org.opengis.referencing.IdentifiedObject
Direct Known Subclasses:
Molodensky.Ellipsoid, Sphere
public class DefaultEllipsoid extends AbstractIdentifiedObject implements org.opengis.referencing.datum.Ellipsoid
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: Some numerical values derived from the above properties are:

Creating new ellipsoid instances

New instances can be created either directly by specifying all information to a factory method (choices 3 and 4 below), or indirectly by specifying the identifier of an entry in a database (choices 1 and 2 below). In particular, the EPSG repository provides definitions for many ellipsoids, and Apache SIS provides convenience shortcuts for some of them.

Choice 1 in the following list is the easiest but most restrictive way to get an ellipsoid. The other choices provide more freedom. Each choice delegates its work to the subsequent items (in the default configuration), so this list can be seen as top to bottom API.

  1. Create an Ellipsoid from one of the static convenience shortcuts listed in CommonCRS.ellipsoid().
  2. Create an Ellipsoid from an identifier in a database by invoking DatumAuthorityFactory.createEllipsoid(String).
  3. Create an Ellipsoid by invoking the DatumFactory.createEllipsoid(…) or createFlattenedSphere(…) method (implemented for example by GeodeticObjectFactory).
  4. Create a DefaultEllipsoid by invoking the createEllipsoid(…) or createFlattenedSphere(…) static methods defined in this class.
Example: the following code gets the WGS84 ellipsoid:

Immutability and thread safety

This class is immutable and thus thread-safe if the property values (not necessarily the map itself) given to the constructors are also immutable. Unless otherwise noted in the javadoc, this condition holds if all components were created using only SIS factories and static constants.
Since:
0.4
Version:
1.3
See Also:

  • Field Details

    • serialVersionUID

      private static final long serialVersionUID
      Serial number for inter-operability with different versions.
      See Also:

    • semiMajorAxis

      private double semiMajorAxis
      The equatorial radius. This field should be considered as final. It is modified only by JAXB at unmarshalling time.
      See Also:

    • semiMinorAxis

      private double semiMinorAxis
      The polar radius. This field should be considered as final. It is modified only by JAXB at unmarshalling time.
      See Also:

    • inverseFlattening

      private double inverseFlattening
      The inverse of the flattening value, or Double.POSITIVE_INFINITY if the ellipsoid is a sphere. This field shall be considered as final. It is modified only by JAXB at unmarshalling time.
      See Also:

    • ivfDefinitive

      private boolean ivfDefinitive
      Tells if the Inverse Flattening is definitive for this ellipsoid. This field shall be considered as final. It is modified only by JAXB at unmarshalling time.
      See Also:

    • unit

      private javax.measure.Unit<javax.measure.quantity.Length> unit
      The units of the semi-major and semi-minor axis values.

  • Constructor Details

    • DefaultEllipsoid

      protected DefaultEllipsoid(Map<String,?> properties, double semiMajorAxis, double semiMinorAxis, double inverseFlattening, boolean ivfDefinitive, javax.measure.Unit<javax.measure.quantity.Length> unit)
      Creates a new ellipsoid using the specified axis length. The properties map is given unchanged to the super-class constructor. The following table is a reminder of main (not all) properties:
      Recognized properties (non exhaustive list)
      Property name Value type Returned by
      "name" ReferenceIdentifier or String AbstractIdentifiedObject.getName()
      "alias" GenericName or CharSequence (optionally as array) AbstractIdentifiedObject.getAlias()
      "identifiers" ReferenceIdentifier (optionally as array) AbstractIdentifiedObject.getIdentifiers()
      "remarks" InternationalString or String AbstractIdentifiedObject.getRemarks()
      Parameters:
      properties - the properties to be given to the identified object.
      semiMajorAxis - the equatorial radius.
      semiMinorAxis - the polar radius.
      inverseFlattening - the inverse of the flattening value.
      ivfDefinitive - true if the inverse flattening is definitive.
      unit - the units of the semi-major and semi-minor axis values.
      See Also:

    • DefaultEllipsoid

      protected DefaultEllipsoid(org.opengis.referencing.datum.Ellipsoid ellipsoid)
      Creates a new ellipsoid with the same values than the specified one. This copy constructor provides a way to convert an arbitrary implementation into a SIS one or a user-defined one (as a subclass), usually in order to leverage some implementation-specific API.

      This constructor performs a shallow copy, i.e. the properties are not cloned.

      Parameters:
      ellipsoid - the ellipsoid to copy.
      See Also:

    • DefaultEllipsoid

      private DefaultEllipsoid()
      Constructs a new object in which every attributes are set to a null value. This is not a valid object. This constructor is strictly reserved to JAXB, which will assign values to the fields using reflection.

  • Method Details

    • createEllipsoid

      public static DefaultEllipsoid createEllipsoid(Map<String,?> properties, double semiMajorAxis, double semiMinorAxis, javax.measure.Unit<javax.measure.quantity.Length> unit)
      Creates a new ellipsoid using the specified properties and axis length. The properties map is given unchanged to the super-class constructor.
      Parameters:
      properties - the properties to be given to the identified object.
      semiMajorAxis - the equatorial radius in the given unit.
      semiMinorAxis - the polar radius in the given unit.
      unit - the units of the semi-major and semi-minor axis values.
      Returns:
      an ellipsoid with the given axis length.
      See Also:

    • createFlattenedSphere

      public static DefaultEllipsoid createFlattenedSphere(Map<String,?> properties, double semiMajorAxis, double inverseFlattening, javax.measure.Unit<javax.measure.quantity.Length> unit)
      Creates a new ellipsoid using the specified properties, axis length and inverse flattening value. The properties map is given unchanged to the super-class constructor.
      Parameters:
      properties - the properties to be given to the identified object.
      semiMajorAxis - the equatorial radius in the given unit.
      inverseFlattening - the inverse flattening value.
      unit - the units of the semi-major and semi-minor axis values.
      Returns:
      an ellipsoid with the given axis length.
      See Also:

    • castOrCopy

      public static DefaultEllipsoid castOrCopy(org.opengis.referencing.datum.Ellipsoid object)
      Returns a SIS ellipsoid implementation with the same values than the given arbitrary implementation. If the given object is null, then this method returns null. Otherwise if the given object is already a SIS implementation, then the given object is returned unchanged. Otherwise a new SIS implementation is created and initialized to the attribute values of the given object.
      Parameters:
      object - the object to get as a SIS implementation, or null if none.
      Returns:
      a SIS implementation containing the values of the given object (may be the given object itself), or null if the argument was null.

    • getInterface

      public Class<? extends org.opengis.referencing.datum.Ellipsoid> getInterface()
      Returns the GeoAPI interface implemented by this class. The SIS implementation returns Ellipsoid.class.
      Note for implementers: Subclasses usually do not need to override this method since GeoAPI does not define Ellipsoid sub-interface. Overriding possibility is left mostly for implementers who wish to extend GeoAPI with their own set of interfaces.
      Overrides:
      getInterface in class AbstractIdentifiedObject
      Returns:
      Ellipsoid.class or a user-defined sub-interface.

    • getAxisUnit

      public javax.measure.Unit<javax.measure.quantity.Length> getAxisUnit()
      Returns the linear unit of the semi-major and semi-minor axis values.
      Specified by:
      getAxisUnit in interface org.opengis.referencing.datum.Ellipsoid
      Returns:
      the axis linear unit.

    • getSemiMajorAxis

      public double getSemiMajorAxis()
      Length of the semi-major axis of the ellipsoid. This is the equatorial radius in axis linear unit.
      Specified by:
      getSemiMajorAxis in interface org.opengis.referencing.datum.Ellipsoid
      Returns:
      length of semi-major axis.

    • getSemiMinorAxis

      public double getSemiMinorAxis()
      Length of the semi-minor axis of the ellipsoid. This is the polar radius in axis linear unit.
      Specified by:
      getSemiMinorAxis in interface org.opengis.referencing.datum.Ellipsoid
      Returns:
      length of semi-minor axis.

    • getAuthalicRadius

      public double getAuthalicRadius()
      Returns the radius of a hypothetical sphere having the same surface than this ellipsoid. The radius is expressed in axis linear unit.
      Returns:
      the radius of a sphere having the same surface than this ellipsoid.
      See Also:

    • getRadius

      public double getRadius(double φ)
      Returns the radius at the given latitude. Special cases:
      Parameters:
      \u03c6 - latitude in degrees, from -90° to +90° inclusive.
      Returns:
      radius at the given latitude.
      Since:
      1.3

    • getEccentricity

      public double getEccentricity()
      The ratio of the distance between the center and a focus of the ellipse to the length of its semi-major axis. The eccentricity can alternately be computed from the equation: ℯ = √(2f - f²) where f is the flattening factor (not inverse).
      Returns:
      ℯ, the eccentricity of this ellipsoid.

    • getEccentricitySquared

      public double getEccentricitySquared()
      Returns the square of the eccentricity value.
      Purpose: this convenience method is provided because ℯ² is frequently used in coordinate operations, actually more often than ℯ. This convenience method avoids the cost of computing the square root when not needed.
      Returns:
      ℯ², the square of the eccentricity value.
      Since:
      0.7

    • eccentricitySquared

      private DoubleDouble eccentricitySquared()
      Computes the square of the eccentricity value with ℯ² = 2f - f².
      Implementation note: we use the flattening factor for this computation because the inverse flattening factor is usually the second defining parameter. But even if the second defining parameter of this ellipsoid was rather the semi-minor axis, the fact that we use double-double arithmetic should give the same result anyway.

    • flattening

      private static DoubleDouble flattening(org.opengis.referencing.datum.Ellipsoid e)
      Computes the flattening factor (not inverse) of the given ellipsoid. This method chooses the formula depending on whether the defining parameter is the inverse flattening factor or the semi-minor axis length. The defining parameters are presumed fully accurate in base 10 (even if this is of course not possible in the reality), because those parameters are definitions given by authorities.
      Analogy: the conversion factor from inches to centimetres is 2.54 by definition. Even if we could find a more accurate value matching historical measurements, the 2.54 value is the internationally agreed value for all conversions. This value is (by convention) defined in base 10 and has no exact double representation.

    • getInverseFlattening

      public double getInverseFlattening()
      Returns the value of the inverse of the flattening constant. Flattening is a value used to indicate how closely an ellipsoid approaches a spherical shape. 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 Double.POSITIVE_INFINITY value is used.
      Specified by:
      getInverseFlattening in interface org.opengis.referencing.datum.Ellipsoid
      Returns:
      the inverse flattening value.

    • isIvfDefinitive

      public 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.
      Specified by:
      isIvfDefinitive in interface org.opengis.referencing.datum.Ellipsoid
      Returns:
      true if the inverse flattening is definitive, or false if the polar radius is definitive.

    • isSphere

      public boolean isSphere()
      true if the ellipsoid is degenerate and is actually a sphere. The sphere is completely defined by the semi-major axis, which is the radius of the sphere.
      Specified by:
      isSphere in interface org.opengis.referencing.datum.Ellipsoid
      Returns:
      true if the ellipsoid is degenerate and is actually a sphere.

    • semiMajorAxisDifference

      public double semiMajorAxisDifference(org.opengis.referencing.datum.Ellipsoid other)
      Returns the difference between the semi-major axis length of two ellipsoids. If the two ellipsoid does not use the same unit of measurement, than the axis length of the other ellipsoid is converted into the units of this ellipsoid axis.
      Example: WGS84.semiMajorAxisDifference(ED50) returns 251 metres. This information is a parameter of Molodensky transformations.
      Parameters:
      other - the other ellipsoid from which to get semi-major axis length difference.
      Returns:
      (other ellipsoid semi-major axis) - (this ellipsoid semi-major axis).
      Since:
      0.7

    • flatteningDifference

      public double flatteningDifference(org.opengis.referencing.datum.Ellipsoid other)
      Returns the difference between the flattening factor of two ellipsoids. This method returns 0 if the two ellipsoids are equal.
      Example: WGS84.flatteningDifference(ED50) returns approximately 1.41927E-05. This information is a parameter of Molodensky transformations.
      Parameters:
      other - the other ellipsoid from which to get flattening difference.
      Returns:
      (other ellipsoid flattening) - (this ellipsoid flattening).
      Since:
      0.7

    • equals

      public boolean equals(Object object, ComparisonMode mode)
      Compares this ellipsoid with the specified object for equality.
      Specified by:
      equals in interface LenientComparable
      Overrides:
      equals in class AbstractIdentifiedObject
      Parameters:
      object - the object to compare to this.
      mode - STRICT for performing a strict comparison, or IGNORE_METADATA for comparing only properties relevant to coordinate transformations.
      Returns:
      true if both objects are equal.
      See Also:

    • computeHashCode

      protected long computeHashCode()
      Invoked by hashCode() for computing the hash code when first needed. See AbstractIdentifiedObject.computeHashCode() for more information.
      Overrides:
      computeHashCode in class AbstractIdentifiedObject
      Returns:
      the hash code value. This value may change in any future Apache SIS version.

    • formatTo

      protected String formatTo(Formatter formatter)
      Formats this ellipsoid as a Well Known Text Ellipsoid[…] element.
      Overrides:
      formatTo in class AbstractIdentifiedObject
      Parameters:
      formatter - the formatter where to format the inner content of this WKT element.
      Returns:
      "Ellipsoid" (WKT 2) or "Spheroid" (WKT 1).
      See Also:

    • afterUnmarshal

      private void afterUnmarshal(Unmarshaller unmarshaller, Object parent)
      After the unmarshalling process, only one value between semiMinorAxis and inverseFlattening has been defined. Since the semiMajorAxis has been defined, it is now possible to calculate the value of the missing parameter using the values of those that are set.
      See Also:

    • getSemiMajorAxisMeasure

      private Measure getSemiMajorAxisMeasure()
      Returns the semi-major axis value as a measurement. This method is invoked by JAXB for XML marshalling.

    • setSemiMajorAxisMeasure

      private void setSemiMajorAxisMeasure(Measure measure)
      Sets the semi-major axis value. This method is invoked by JAXB at unmarshalling time only.
      See Also:

    • getSecondDefiningParameter

      private SecondDefiningParameter getSecondDefiningParameter()
      Returns the object to be marshalled as the SecondDefiningParameter XML element. The returned object contains the values for semiMinorAxis or inverseFlattening, according to the isIvfDefinitive() value. This method is for JAXB marshalling only.

    • setSecondDefiningParameter

      private void setSecondDefiningParameter(SecondDefiningParameter second)
      Sets the second defining parameter value, either the inverse of the flattening value or the semi minor axis value, according to what have been defined in the second defining parameter given. This is for JAXB unmarshalling process only.
      See Also:

    • harmonizeAxisUnits

      private void harmonizeAxisUnits(javax.measure.Unit<javax.measure.quantity.Length> uom)
      Ensures that the semi-minor axis uses the same unit than the semi-major one. The unit field shall be set to the semi-major axis unit before this method call.
      Parameters:
      uom - the semi-minor axis unit.