Module org.apache.sis.referencing
Package org.apache.sis.referencing.datum

Class DefaultGeodeticDatum

Object
FormattableObject
AbstractIdentifiedObject
AbstractDatum
DefaultGeodeticDatum
All Implemented Interfaces:
Serializable, Formattable, Deprecable, Lenient­Comparable, Datum, Geodetic­Datum, Identified­Object
public class DefaultGeodeticDatum extends AbstractDatum implements GeodeticDatum
Defines the location and orientation of an ellipsoid that approximates the shape of the earth. Geodetic datum are used together with ellipsoidal coordinate system, and also with Cartesian coordinate system centered in the ellipsoid (or sphere).

Bursa-Wolf parameters

One or many Bursa­Wolf­Parameters can optionally be associated to each Default­Geodetic­Datum instance. This association is not part of the ISO 19111 model, but still a common practice (especially in older standards). Associating Bursa-Wolf parameters to geodetic datum is known as the early-binding approach. A recommended alternative, discussed below, is the late-binding approach.

The Bursa-Wolf parameters serve two purposes:

  1. Fallback for datum shifts
    There is different methods for transforming coordinates from one geodetic datum to another datum, and Bursa-Wolf parameters are used with some of them. However, different set of parameters may exist for the same pair of (source, target) datum, so it is often not sufficient to know those datum. The (source, target) pair of CRS are often necessary, sometimes together with the geographic extent of the coordinates to transform.

    Apache SIS searches for datum shift methods (including Bursa-Wolf parameters) in the EPSG database when a Coordinate­Operation or a Math­Transform is requested for a pair of CRS. This is known as the late-binding approach. If a datum shift method is found in the database, it will have precedence over any Bursa­Wolf­Parameters instance associated to this Default­Geodetic­Datum. Only if no datum shift method is found in the database, then the Bursa­Wolf­Parameters associated to the datum may be used as a fallback.

  2. WKT version 1 formatting
    The Bursa-Wolf parameters association serves another purpose: when a CRS is formatted in the older Well Known Text (WKT 1) format, the formatted string may contain a TOWGS84[…] element with the parameter values of the transformation to the WGS 84 datum. This element is provided as a help for other Geographic Information Systems that support only the early-binding approach. Apache SIS usually does not need the TOWGS84 element, except as a fallback for datum that do not exist in the EPSG database.

Creating new geodetic datum 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). Choice 1 in the following list is the easiest but most restrictive way to get a geodetic datum. The other choices provide more freedom.
  1. Create a Geodetic­Datum from one of the static convenience shortcuts listed in Common­CRS​.datum().
  2. Create a Geodetic­Datum from an identifier in a database by invoking Datum­Authority­Factory​.create­Geodetic­Datum(String).
  3. Create a Geodetic­Datum by invoking the Datum­Factory​.create­Geodetic­Datum(…) method (implemented for example by Geodetic­Object­Factory).
  4. Create a Default­Geodetic­Datum by invoking the constructor.
Example: the following code gets a World Geodetic System 1984 datum: 
GeodeticDatum datum = CommonCRS.WGS84.datum();

Immutability and thread safety

This class is immutable and thus thread-safe if the property values (not necessarily the map itself), the Ellipsoid and the Prime­Meridian given to the constructor 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
See Also:

  • Field Details

  • Constructor Details

  • Method Details

    • castOrCopy

      public static DefaultGeodeticDatum castOrCopy(GeodeticDatum object)
      Returns a SIS datum 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 GeodeticDatum> getInterface()
      Returns the GeoAPI interface implemented by this class. The SIS implementation returns Geodetic­Datum​.class.

      Note for implementers

      Subclasses usually do not need to override this method since GeoAPI does not define Geodetic­Datum sub-interface. Overriding possibility is left mostly for implementers who wish to extend GeoAPI with their own set of interfaces.
      Overrides:
      get­Interface in class Abstract­Datum
      Returns:
      Geodetic­Datum​.class or a user-defined sub-interface.

    • getEllipsoid

      public Ellipsoid getEllipsoid()
      Returns the ellipsoid given at construction time.
      Specified by:
      get­Ellipsoid in interface Geodetic­Datum
      Returns:
      the ellipsoid.

    • getPrimeMeridian

      public PrimeMeridian getPrimeMeridian()
      Returns the prime meridian given at construction time.
      Specified by:
      get­Prime­Meridian in interface Geodetic­Datum
      Returns:
      the prime meridian.

    • getBursaWolfParameters

      public BursaWolfParameters[] getBursaWolfParameters()
      Returns all Bursa-Wolf parameters specified in the properties map at construction time. See class javadoc for a discussion about Bursa-Wolf parameters.
      Returns:
      the Bursa-Wolf parameters, or an empty array if none.

    • getPositionVectorTransformation

      public Matrix getPositionVectorTransformation(GeodeticDatum targetDatum, Extent areaOfInterest)
      Returns the position vector transformation (geocentric domain) to the specified datum. If the returned matrix is non-null, then the transformation is represented by an affine transform which can be applied on geocentric coordinates. This is identified in the EPSG database as operation method 1033 – Position Vector transformation (geocentric domain), or 1053 – Time-dependent Position Vector transformation.

      If this datum and the given target­Datum do not use the same prime meridian, then it is caller's responsibility to apply longitude rotation before to use the matrix returned by this method. The target prime meridian should be Greenwich (see constructor javadoc), in which case the datum shift should be applied in a geocentric coordinate system having Greenwich as the prime meridian.

      Note: in EPSG dataset version 8.9, all datum shifts that can be represented by this method use Greenwich as the prime meridian, both in source and target datum.

      Search criteria

      If the given area­Of­Interest is non-null and contains at least one geographic bounding box, then this method ignores any Bursa-Wolf parameters having a domain of validity that does not intersect the given geographic extent. This method performs the search among the remaining parameters in the following order:
      1. If this Geodetic­Datum contains Bursa­Wolf­Parameters having the given target datum (ignoring metadata), then the matrix will be built from those parameters.
      2. Otherwise if the other datum contains Bursa­Wolf­Parameters having this datum as their target (ignoring metadata), then the matrix will be built from those parameters and inverted.

      Multi-occurrences resolution

      If more than one Bursa­Wolf­Parameters instance is found in any of the above steps, then the one having the largest intersection between its domain of validity and the given extent will be selected. If more than one instance have the same intersection, then the first occurrence is selected.

      Time-dependent parameters

      If the given extent contains a temporal extent, then the instant located midway between start and end time will be taken as the date where to evaluate the Bursa-Wolf parameters. This is relevant only to time-dependent parameters.
      Parameters:
      target­Datum - the target datum.
      area­Of­Interest - the geographic and temporal extent where the transformation should be valid, or null.
      Returns:
      an affine transform from this to target in geocentric space, or null if none.
      See Also:

    • isHeuristicMatchForName

      public boolean isHeuristicMatchForName(String name)
      Returns true if either the primary name or at least one alias matches the given string according heuristic rules. This method implements the flexibility documented in the super-class. In particular, this method ignores the prime meridian name if that name is found between parenthesis in the datum name. The meridian can be safely ignored in the datum name because the Prime­Meridian object is already compared by the Abstract­Identified­Object​.equals(Object) method.

      Example

      If the datum name is "Nouvelle Triangulation Française (Paris)" and the prime meridian name is "Paris", then this method compares only the "Nouvelle Triangulation Française" part.

      Future evolutions

      This method implements heuristic rules learned from experience while trying to provide inter-operability with different data producers. Those rules may be adjusted in any future SIS version according experience gained while working with more data producers.
      Overrides:
      is­Heuristic­Match­For­Name in class Abstract­Datum
      Parameters:
      name - the name to compare.
      Returns:
      true if the primary name or at least one alias matches the specified name.
      Since:
      0.7
      See Also:

    • equals

      public boolean equals(Object object, ComparisonMode mode)
      Compares this datum with the specified object for equality.
      Specified by:
      equals in interface Lenient­Comparable
      Overrides:
      equals in class Abstract­Datum
      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 datum as a Well Known Text Datum[…] element.

      Example

      Well-Known Text of a WGS 84 datum. 
      Datum["World Geodetic System 1984",
  Ellipsoid["WGS84", 6378137.0, 298.257223563, LengthUnit["metre", 1]],
Id["EPSG", 6326, Citation["IOGP"], URI["urn:ogc:def:datum:EPSG::6326"]]]

      Same datum using WKT 1.

      DATUM["World Geodetic System 1984"
  SPHEROID["WGS84", 6378137.0, 298.257223563],
AUTHORITY["EPSG", "6326"]]
      Note that the prime meridian shall be formatted by the caller as a separated element after the geodetic datum (for compatibility with WKT 1).
      Overrides:
      format­To in class Abstract­Datum
      Parameters:
      formatter - the formatter where to format the inner content of this WKT element.
      Returns:
      "Datum" or "Geodetic­Datum".
      See Also: