# Class DefaultPrimeMeridian

Object
FormattableObject
AbstractIdentifiedObject
DefaultPrimeMeridian

All Implemented Interfaces:
  `Serializable`, `Formattable`, `Deprecable`, `LenientComparable`, `Printable`, `PrimeMeridian`, `IdentifiedObject`

public class DefaultPrimeMeridian extends AbstractIdentifiedObject implements PrimeMeridian
Defines the origin from which longitude values are determined.

## Creating new prime meridian 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 prime meridians, 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 a prime meridian. 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 a `PrimeMeridian` from one of the static convenience shortcuts listed in `CommonCRS​.primeMeridian()`.
2. Create a `PrimeMeridian` from an identifier in a database by invoking `DatumAuthorityFactory​.createPrimeMeridian(String)`.
3. Create a `PrimeMeridian` by invoking the `DatumFactory​.createPrimeMeridian(…)` method (implemented for example by `GeodeticObjectFactory`).
4. Create a `DefaultPrimeMeridian` by invoking the constructor.

Example: the following code gets the Greenwich prime meridian:

    PrimeMeridian pm = CommonCRS.WGS84.primeMeridian();

## Immutability and thread safety

This class is immutable and thus thread-safe if the property values (not necessarily the map itself) 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:
  - `CommonCRS​.primeMeridian()`
  - `GeodeticAuthorityFactory​.createPrimeMeridian(String)`
  - Serialized Form

- ## Field Summary

  ### Fields inherited from class AbstractIdentifiedObject

  `DEPRECATED_KEY, DOMAINS_KEY, LOCALE_KEY`

  ### Fields inherited from interface IdentifiedObject

  `ALIAS_KEY, IDENTIFIERS_KEY, NAME_KEY, REMARKS_KEY`

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  ``
  `DefaultPrimeMeridian(Map<String,?> properties, double greenwichLongitude, Unit<Angle> angularUnit)`
  Creates a prime meridian from the given properties.
  `protected`
  `DefaultPrimeMeridian(PrimeMeridian meridian)`
  Creates a new prime meridian with the same values as the specified one.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `static DefaultPrimeMeridian`
  `castOrCopy(PrimeMeridian object)`
  Returns a SIS prime meridian implementation with the same values as the given arbitrary implementation.
  `protected String`
  `formatTo(Formatter formatter)`
  Formats this prime meridian as a Well Known Text `PrimeMeridian[…]` element.
  `Unit<Angle>`
  `getAngularUnit()`
  Returns the angular unit of the Greenwich longitude.
  `double`
  `getGreenwichLongitude()`
  Longitude of the prime meridian measured from the Greenwich meridian, positive eastward.
  `double`
  `getGreenwichLongitude(Unit<Angle> unit)`
  Returns the longitude value relative to the Greenwich Meridian, expressed in the specified units.
  `Class<? extends PrimeMeridian>`
  `getInterface()`
  Returns the GeoAPI interface implemented by this class.

  ### Methods inherited from class AbstractIdentifiedObject

  `castOrCopy, equals, formatTo, getAlias, getDescription, getDomains, getIdentifiers, getName, getRemarks, hashCode, isDeprecated, isHeuristicMatchForName`

  ### Methods inherited from class FormattableObject

  `print, toString, toString, toWKT`

  ### Methods inherited from class Object

  `clone, finalize, getClass, notify, notifyAll, wait, wait, wait`

  ### Methods inherited from interface IdentifiedObject

  `getAlias, getIdentifiers, getName, getRemarks, toWKT`

- ## Constructor Details

  - ### DefaultPrimeMeridian

    public DefaultPrimeMeridian(Map<String,?> properties, double greenwichLongitude, Unit<Angle> angularUnit)
    Creates a prime meridian from the given properties. 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.
      `greenwichLongitude` - the longitude value relative to the Greenwich Meridian.
      `angularUnit` - the angular unit of the longitude.
    See Also:
      - `GeodeticObjectFactory​.createPrimeMeridian(Map, double, Unit)`

  - ### DefaultPrimeMeridian

    protected DefaultPrimeMeridian(PrimeMeridian meridian)
    Creates a new prime meridian with the same values as 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:
      `meridian` - the prime meridian to copy.
    See Also:
      - `castOrCopy(PrimeMeridian)`

- ## Method Details

  - ### castOrCopy

    public static DefaultPrimeMeridian castOrCopy(PrimeMeridian object)
    Returns a SIS prime meridian implementation with the same values as 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 PrimeMeridian> getInterface()
    Returns the GeoAPI interface implemented by this class. The SIS implementation returns `PrimeMeridian​.class`.

    #### Note for implementers

    Subclasses usually do not need to override this method since GeoAPI does not define `PrimeMeridian` 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:
      `PrimeMeridian​.class` or a user-defined sub-interface.

  - ### getGreenwichLongitude

    public double getGreenwichLongitude()
    Longitude of the prime meridian measured from the Greenwich meridian, positive eastward.
    Specified by:
      `getGreenwichLongitude` in interface `PrimeMeridian`
    Returns:
      the prime meridian Greenwich longitude, in angular unit.

  - ### getGreenwichLongitude

    public double getGreenwichLongitude(Unit<Angle> unit)
    Returns the longitude value relative to the Greenwich Meridian, expressed in the specified units. This convenience method makes it easier to obtain longitude in decimal degrees using the following code, regardless of the underlying angular units of this prime meridian:

        double longitudeInDegrees = primeMeridian.getGreenwichLongitude(Units.DEGREE);

    Parameters:
      `unit` - the unit in which to express longitude.
    Returns:
      the Greenwich longitude in the given units.

  - ### getAngularUnit

    public Unit<Angle> getAngularUnit()
    Returns the angular unit of the Greenwich longitude.
    Specified by:
      `getAngularUnit` in interface `PrimeMeridian`
    Returns:
      the angular unit of the Greenwich longitude.

  - ### formatTo

    protected String formatTo(Formatter formatter)
    Formats this prime meridian as a Well Known Text `PrimeMeridian[…]` element.
    Overrides:
      `formatTo` in class `AbstractIdentifiedObject`
    Parameters:
      `formatter` - the formatter where to format the inner content of this WKT element.
    Returns:
      `"PrimeMeridian"` (WKT 2) or `"PrimeM"` (WKT 1).
    See Also:
      - `FormattableObject​.toWKT()`
      - `FormattableObject​.toString()`