# Interface PrimeMeridian

All Superinterfaces:
  `IdentifiedObject`

All Known Implementing Classes:
  `DefaultPrimeMeridian`

@UML(identifier="CD_PrimeMeridian", specification=ISO_19111) public interface PrimeMeridian extends IdentifiedObject
A prime meridian defines the origin from which longitude values are determined. The default name is "Greenwich", and that value shall be used when the greenwich longitude value is zero.

Since:
  1.0

- ## Field Summary

  ### Fields inherited from interface IdentifiedObject

  `ALIAS_KEY, IDENTIFIERS_KEY, NAME_KEY, REMARKS_KEY`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `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.

  ### Methods inherited from interface IdentifiedObject

  `getAlias, getIdentifiers, getName, getRemarks, toWKT`

- ## Method Details

  - ### getGreenwichLongitude

    @UML(identifier="greenwichLongitude", obligation=CONDITIONAL, specification=ISO_19111) double getGreenwichLongitude()
    Longitude of the prime meridian measured from the Greenwich meridian, positive eastward. The `greenwichLongitude` initial value is zero, and that value shall be used when the meridian name value is "Greenwich".
    Returns:
      The prime meridian Greenwich longitude, in angular unit.

  - ### getAngularUnit

    @UML(identifier="getAngularUnit", specification=OGC_01009) Unit<Angle> getAngularUnit()
    Returns the angular unit of the Greenwich longitude.
    Returns:
      The angular unit of greenwich longitude.