org.apache.sis.referencing.cs

## Class CoordinateSystems

- Object
- - Static
  - - CoordinateSystems

-     public final class CoordinateSystems
      extends Static

  Utility methods working on `CoordinateSystem` objects and their axes. Those methods allow for example to estimate an angle between two axes or determining the change of axis directions and units between two coordinate systems.
  Since:
    0.4

  Defined in the `sis-referencing` module

- - ### Method Summary

    All Methods Static Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `static Angle` | `angle(AxisDirection source, AxisDirection target)` Returns the arithmetic (counterclockwise) angle from the first axis direction to the second direction.
    `static AxisDirection` | `directionAlongMeridian(AxisDirection baseDirection, double meridian)` Returns an axis direction from a pole along a meridian.
    `static AxisDirection[]` | `getAxisDirections(CoordinateSystem cs)` Returns the axis directions for the specified coordinate system.
    `static Integer` | `getEpsgCode(Unit<?> unit, AxisDirection... directions)` Returns the EPSG code of a coordinate system using the given unit and axis directions.
    `static AxisDirection` | `parseAxisDirection(String name)` Returns an axis direction code from the given direction name.
    `static CoordinateSystem` | `replaceAngularUnit(CoordinateSystem cs, Unit<Angle> newUnit)` Returns a coordinate system derived from the given one but with all angular units replaced by the given unit.
    `static CoordinateSystem` | `replaceAxes(CoordinateSystem cs, AxisFilter filter)` Returns a coordinate system derived from the given one but with a modified list of axes.
    `static CoordinateSystem` | `replaceLinearUnit(CoordinateSystem cs, Unit<Length> newUnit)` Returns a coordinate system derived from the given one but with all linear units replaced by the given unit.
    `static Matrix` | `swapAndScaleAxes(CoordinateSystem sourceCS, CoordinateSystem targetCS)` Returns an affine transform between two coordinate systems.

    - ### Methods inherited from class Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Method Detail

    - #### parseAxisDirection

          public static AxisDirection parseAxisDirection(String name)
                                                  throws IllegalArgumentException

      Returns an axis direction code from the given direction name. Names are case-insensitive. They may be:
      - Cardinal directions like "north" and "east".
      - Inter-cardinal directions "north-east" and "south-south-east", using either `'-'`, `'_'` or spaces as separator between the cardinal points.
      - Directions from a pole like "South along 180 deg" and "South along 90° East", using either the `"deg"` or `"°"` symbol. Note that the meridian is not necessarily relative to Greenwich (see `directionAlongMeridian(…)` for more information).
      Parameters:
        `name` - the direction name (e.g. "north", "north-east", etc.).
      Returns:
        the axis direction for the given name.
      Throws:
        `IllegalArgumentException` - if the given name is not a known axis direction.

    - #### directionAlongMeridian

          public static AxisDirection directionAlongMeridian(AxisDirection baseDirection,
                                                             double meridian)

      Returns an axis direction from a pole along a meridian. The given meridian is usually, but not necessarily, relative to the Greenwich meridian.
      Example: `directionAlongMeridian(AxisDirection​.SOUTH, -90)` returns an axis direction for “South along 90°W”.
      Reference meridian
      The reference meridian depends on the context. It is usually the prime meridian of the geodetic datum of the geographic CRS instance that contains (through its coordinate system) the axes having those directions. This policy is consistent with WKT 2 specification §7.5.4(iv).
      Parameters:
        `baseDirection` - the base direction, which must be `AxisDirection​.NORTH` or `AxisDirection​.SOUTH`.
        `meridian` - the meridian in degrees, relative to a unspecified (usually Greenwich) prime meridian. Meridians in the East hemisphere are positive and meridians in the West hemisphere are negative.
      Returns:
        the axis direction along the given meridian.
      Since:
        0.6

    - #### angle

          public static Angle angle(AxisDirection source,
                                    AxisDirection target)

      Returns the arithmetic (counterclockwise) angle from the first axis direction to the second direction. This method returns a value between -180° and +180°, or `null` if no angle can be computed.
      Horizontal directions
      For any pair of compass directions which are not opposite directions, a positive angle denotes a right-handed system while a negative angle denotes a left-handed system. Examples:
      - The angle from `EAST` to `NORTH` is 90°
      - The angle from `SOUTH` to `WEST` is -90°
      - The angle from "North along 90° East" to "North along 0°" is 90°.
      Note: in the case of directions like “South along 90°W”, the caller is responsible to make sure that the meridians are relative to the same prime meridian. This is the case if the axes are part of the same `CoordinateSystem` instance.
      Horizontal and vertical directions
      By convention this method defines the angle from any compass direction to the `UP` vertical direction as 90°, and the angle of any compass direction to the `DOWN` vertical direction as -90°. The sign of those angles gives no indication about whether the coordinate system is right-handed or left-handed. Those angles are returned as instances of `ElevationAngle`.

      All angles are approximative since this method does not take the Earth ellipsoidal or geoidal shape in account.

      Invariants
      For any non-null return value:
      - `angle(A, A) = 0°`
      - `angle(A, opposite(A)) = ±180°`
      - `angle(A, B) = -angle(B, A)`
      Parameters:
        `source` - the source axis direction.
        `target` - the target axis direction.
      Returns:
        the arithmetic angle (in degrees) of the rotation to apply on a line pointing toward the source direction in order to make it point toward the target direction, or `null` if this value can not be computed.

    - #### swapAndScaleAxes

          public static Matrix swapAndScaleAxes(CoordinateSystem sourceCS,
                                                CoordinateSystem targetCS)
                                         throws IllegalArgumentException,
                                                IncommensurableException

      Returns an affine transform between two coordinate systems. Only units and axes order (e.g. transforming from (North, West) to (East, North) are taken in account by this method.
      Conditions
      The two coordinate systems must implement the same GeoAPI coordinate system interface. For example if `sourceCS` is a `CartesianCS`, then `targetCS` must be a `CartesianCS` too.
      Example: If coordinates in `sourceCS` are (x,y) tuples in metres and coordinates in `targetCS` are (-y,x) tuples in centimetres, then the transformation can be performed as below:

          ┌      ┐   ┌                ┐ ┌     ┐
          │-y(cm)│   │   0  -100    0 │ │ x(m)│
          │ x(cm)│ = │ 100     0    0 │ │ y(m)│
          │ 1    │   │   0     0    1 │ │ 1   │
          └      ┘   └                ┘ └     ┘

      Parameters:
        `sourceCS` - the source coordinate system.
        `targetCS` - the target coordinate system.
      Returns:
        the conversion from `sourceCS` to `targetCS` as an affine transform. Only axis direction and units are taken in account.
      Throws:
        `IllegalArgumentException` - if the CS are not of the same type, or axes do not match.
        `IncommensurableException` - if the units are not compatible, or the conversion is non-linear.
      See Also:
        `Matrices​.createTransform(AxisDirection[], AxisDirection[])`

    - #### replaceAxes

          public static CoordinateSystem replaceAxes(CoordinateSystem cs,
                                                     AxisFilter filter)

      Returns a coordinate system derived from the given one but with a modified list of axes. The axes may be filtered (excluding some axes), reordered or have their unit and direction modified.
      Example: for replacing all angular units of a coordinate system to degrees (regardless what the original angular units were) while leaving other kinds of units unchanged, one can write:

          CoordinateSystem cs = ...;
          cs = CoordinateSystems.replaceAxes(cs, new AxisFilter() {
              @Override
              public Unit<?> getUnitReplacement(CoordinateSystemAxis axis, Unit<?> unit) {
                  if (Units.isAngular(unit)) {
                      unit = Units.DEGREE;
                  }
                  return unit;
              }
          });

      Coordinate system normalization
      This method is often used together with `swapAndScaleAxes(…)` for normalizing the coordinate values given to a math transform.
      Example:

          CoordinateSystem sourceCS = ...;
          CoordinateSystem targetCS = ...;
          Matrix step1 = swapAndScaleAxes(sourceCS, replaceAxes(sourceCS, AxisConvention.NORMALIZED));
          Matrix step2 = ...; // some transform working on coordinates with standard axis order and unit.
          Matrix step3 = swapAndScaleAxes(replaceAxes(targetCS, AxisConvention.NORMALIZED), targetCS);

      A rational for normalized axis order and units is explained in the Axis units and direction section in the description of the map projection package.
      Parameters:
        `cs` - the coordinate system, or `null`.
        `filter` - the modifications to apply on coordinate system axes.
      Returns:
        the modified coordinate system as a new instance, or `cs` if the given coordinate system was null or does not need any change.
      Throws:
        `IllegalArgumentException` - if the specified coordinate system can not be normalized.
      Since:
        0.6
      See Also:
        `AxesConvention​.NORMALIZED`

    - #### replaceLinearUnit

          public static CoordinateSystem replaceLinearUnit(CoordinateSystem cs,
                                                           Unit<Length> newUnit)

      Returns a coordinate system derived from the given one but with all linear units replaced by the given unit. Non-linear units (e.g. angular or scale units) are left unchanged.

      This convenience method is equivalent to the following code:

          return CoordinateSystems.replaceAxes(cs, new AxisFilter() {
              @Override public Unit<?> getUnitReplacement(CoordinateSystemAxis axis, Unit<?> unit) {
                  return Units.isLinear(unit) ? newUnit : unit;
              }
          });

      Parameters:
        `cs` - the coordinate system in which to replace linear units, or `null`.
        `newUnit` - the new linear unit.
      Returns:
        the modified coordinate system as a new instance, or `null` if the given `cs` was null, or `cs` if all linear units were already equal to the given one.
      Since:
        0.7
      See Also:
        `Units​.isLinear(Unit)`

    - #### replaceAngularUnit

          public static CoordinateSystem replaceAngularUnit(CoordinateSystem cs,
                                                            Unit<Angle> newUnit)

      Returns a coordinate system derived from the given one but with all angular units replaced by the given unit. Non-angular units (e.g. linear or scale units) are left unchanged.

      This convenience method is equivalent to the following code:

          return CoordinateSystems.replaceAxes(cs, new AxisFilter() {
              @Override public Unit<?> getUnitReplacement(CoordinateSystemAxis axis, Unit<?> unit) {
                  return Units.isAngular(unit) ? newUnit : unit;
              }
          });

      Parameters:
        `cs` - the coordinate system in which to replace angular units, or `null`.
        `newUnit` - the new angular unit.
      Returns:
        the modified coordinate system as a new instance, or `null` if the given `cs` was null, or `cs` if all angular units were already equal to the given one.
      Since:
        0.7
      See Also:
        `Units​.isAngular(Unit)`

    - #### getAxisDirections

          public static AxisDirection[] getAxisDirections(CoordinateSystem cs)

      Returns the axis directions for the specified coordinate system. This method guarantees that the returned array is non-null and does not contain any null direction.
      Parameters:
        `cs` - the coordinate system.
      Returns:
        the axis directions for the specified coordinate system.
      Throws:
        `NullArgumentException` - if `cs` is null, or one of its axes is null, or a value returned by `CoordinateSystemAxis​.getDirection()` is null.
      Since:
        0.8

    - #### getEpsgCode

          public static Integer getEpsgCode(Unit<?> unit,
                                            AxisDirection... directions)

      Returns the EPSG code of a coordinate system using the given unit and axis directions. If no suitable coordinate system is known to Apache SIS, then this method returns `null`.

      Current implementation uses a hard-coded list of known coordinate systems; it does not yet scan the EPSG database (this may change in future Apache SIS version). The current list of known coordinate systems is given below.

      Known coordinate systems (CS)
      EPSG | CS type | Axis directions | Unit
      --- | --- | --- | ---
      6424 | Ellipsoidal | east | north | degree
      6422 | Ellipsoidal | north | east | degree
      6425 | Ellipsoidal | east | north | grads
      6403 | Ellipsoidal | north | east | grads
      6429 | Ellipsoidal | east | north | radian
      6428 | Ellipsoidal | north | east | radian
      4400 | Cartesian | east | north | metre
      4500 | Cartesian | north | east | metre
      4491 | Cartesian | west | north | metre
      4501 | Cartesian | north | west | metre
      6503 | Cartesian | west | south | metre
      6501 | Cartesian | south | west | metre
      1039 | Cartesian | east | north | foot
      1029 | Cartesian | north | east | foot
      4403 | Cartesian | east | north | Clarke’s foot
      4502 | Cartesian | north | east | Clarke’s foot
      4497 | Cartesian | east | north | US survey foot

      Parameters:
        `unit` - desired unit of measurement.
        `directions` - desired axis directions.
      Returns:
        EPSG codes for a coordinate system using the given axis directions and unit of measurement, or `null` if unknown to this method. Note that a null value does not mean that a more extensive search in the EPSG database would not find a matching coordinate system.
      Since:
        0.8
      See Also:
        `Units​.getEpsgCode(Unit, boolean)`, `GeodeticAuthorityFactory​.createCoordinateSystem(String)`

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