# Class TransformSeparator

Object
TransformSeparator

public class TransformSeparator extends Object
Extracts a sub-transform from a given `MathTransform` and source or target dimension indices. Given an arbitrary `MathTransform`, this class tries to return a new math transform that operates only on a given set of source or target dimensions.

## Example

If the supplied `transform` has (x,y,z) inputs and (λ,φ,h) outputs, then the following code:

    var s = new TransformSeparator(theTransform);
    s.addSourceDimensionRange(0, 2);
    MathTransform mt = s.separate();

will return a transform with (x,y) inputs and (probably) (λ,φ) outputs. The output dimensions can be verified with a call to `getTargetDimensions()`.

Since:
  0.7

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected int[]`
  `sourceDimensions`
  Indices of transform input dimensions to keep, or `null` if not yet defined.
  `protected int[]`
  `targetDimensions`
  Indices of transform output dimensions to keep, or `null` if not yet defined.
  `protected final MathTransform`
  `transform`
  The transform to separate.

- ## Constructor Summary

  Constructors
  Constructor
  Description
  `TransformSeparator(MathTransform transform)`
  Constructs a separator for the given transform.
  `TransformSeparator(MathTransform transform, MathTransformFactory factory)`
  Constructs a separator for the given transform and using the given factory.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `void`
  `addSourceDimensionRange(int lower, int upper)`
  Adds a range of input dimensions to keep in the separated transform.
  `void`
  `addSourceDimensions(int... dimensions)`
  Adds input dimensions to keep in the separated transform.
  `void`
  `addTargetDimensionRange(int lower, int upper)`
  Adds a range of output dimensions to keep in the separated transform.
  `void`
  `addTargetDimensions(int... dimensions)`
  Adds output dimensions to keep in the separated transform.
  `void`
  `clear()`
  Resets this transform separator in the same state as after construction.
  `protected MathTransform`
  `filterSourceDimensions(MathTransform step, int[] dimensions)`
  Creates a transform for the same mathematic as the given `step` but expecting only the given dimensions as inputs.
  `protected MathTransform`
  `filterTargetDimensions(MathTransform step, int[] dimensions)`
  Creates a transform for the same mathematic as the given `step` but producing only the given dimensions as outputs.
  `int[]`
  `getSourceDimensions()`
  Returns the input dimensions to keep or kept in the separated transform.
  `int[]`
  `getTargetDimensions()`
  Returns the output dimensions to keep or kept in the separated transform.
  `boolean`
  `isSourceExpandable()`
  Returns whether `separate()` is allowed to expand the list of source dimensions.
  `MathTransform`
  `replace(int lower, int upper, MathTransform replacement)`
  Replaces the transform in the given range of coordinate indexes.
  `MathTransform`
  `separate()`
  Separates the math transform specified at construction time for given dimension indices.
  `void`
  `setSourceExpandable(boolean enabled)`
  Sets whether `separate()` is allowed to expand the list of source dimensions.

  ### Methods inherited from class Object

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

- ## Field Details

  - ### transform

    protected final MathTransform transform
    The transform to separate.

  - ### sourceDimensions

    protected int[] sourceDimensions
    Indices of transform input dimensions to keep, or `null` if not yet defined. If non-null, the indices in the array must be sorted in strictly increasing order. This sequence can contain any integers in the range 0 inclusive to `MathTransform​.getSourceDimensions()` exclusive.

    Values in this array should never be modified. For adding, removing or editing indices, new arrays should be created and assigned to this field. This approach makes easier to keep snapshots of indices arrays at various stages during the process of separating a `MathTransform`.

    See Also:
      - `getSourceDimensions()`
      - `addSourceDimensions(int...)`
      - `addSourceDimensionRange(int, int)`

  - ### targetDimensions

    protected int[] targetDimensions
    Indices of transform output dimensions to keep, or `null` if not yet defined. If non-null, the indices in the array must be sorted in strictly increasing order. This sequence can contain any integers in the range 0 inclusive to `MathTransform​.getTargetDimensions()` exclusive.

    Values in this array should never be modified. For adding, removing or editing indices, new arrays should be created and assigned to this field. This approach makes easier to keep snapshots of indices arrays at various stages during the process of separating a `MathTransform`.

    See Also:
      - `getTargetDimensions()`
      - `addTargetDimensions(int...)`
      - `addTargetDimensionRange(int, int)`

- ## Constructor Details

  - ### TransformSeparator

    public TransformSeparator(MathTransform transform)
    Constructs a separator for the given transform.
    Parameters:
      `transform` - the transform to separate.

  - ### TransformSeparator

    public TransformSeparator(MathTransform transform, MathTransformFactory factory)
    Constructs a separator for the given transform and using the given factory.
    Parameters:
      `transform` - the transform to separate.
      `factory` - the factory to use for creating new math transforms, or `null` if none.

- ## Method Details

  - ### clear

    public void clear()
    Resets this transform separator in the same state as after construction. This method clears any source and target dimensions settings and disables source expansion. This method can be invoked when the same `MathTransform` needs to be separated in more than one part, for example an horizontal and a vertical component.

  - ### addSourceDimensions

    public void addSourceDimensions(int... dimensions) throws IllegalArgumentException
    Adds input dimensions to keep in the separated transform. The given values are source dimension indices of the transform given to the constructor.

    Constraints:

    - All numbers shall be in the range 0 inclusive to `MathTransform​.getSourceDimensions()` exclusive.
    - The `dimensions` values shall be in strictly increasing order.
    - The `dimensions` values shall be greater than all values specified by all previous calls of this method since construction or since the last call to `clear()`.
    Parameters:
      `dimensions` - a sequence of source dimensions to keep, in strictly increasing order.
    Throws:
      `IllegalArgumentException` - if `dimensions` contains negative values or if values are not in a strictly increasing order.

  - ### addSourceDimensionRange

    public void addSourceDimensionRange(int lower, int upper) throws IllegalArgumentException
    Adds a range of input dimensions to keep in the separated transform. The `lower` and `upper` values define a range of source dimension indices of the transform given to the constructor.
    Parameters:
      `lower` - the lower dimension, inclusive. Shall not be smaller than 0.
      `upper` - the upper dimension, exclusive. Shall be smaller than `MathTransform​.getSourceDimensions()`.
    Throws:
      `IllegalArgumentException` - if `lower` or `upper` are out of bounds.

  - ### getSourceDimensions

    public int[] getSourceDimensions() throws IllegalStateException
    Returns the input dimensions to keep or kept in the separated transform. This method performs the first applicable action in the following list:
    1. Source dimensions have been explicitly set by at least one call to `addSourceDimensions(int...)` or `addSourceDimensionRange(int, int)` since construction or since last call to `clear()`. In such case, this method returns all specified source dimensions.
    2. No source dimensions were set but `separate()` has been invoked. In such case, this method returns the sequence of source dimensions that `separate()` chooses to retain. It may be all source dimensions of the transform given at construction time, but not necessarily.
    3. Otherwise an exception is thrown.
    If source dimensions have not been set explicitly, `TransformSeparator` tries to reduce the set of source dimensions to the smallest set required for computing the target dimensions.
    Returns:
      the input dimension as a sequence of strictly increasing values.
    Throws:
      `IllegalStateException` - if input dimensions have not been set and `separate()` has not yet been invoked.

  - ### addTargetDimensions

    public void addTargetDimensions(int... dimensions) throws IllegalArgumentException
    Adds output dimensions to keep in the separated transform. The given values are target dimension indices of the transform given to the constructor.

    Constraints:

    - All numbers shall be in the range 0 inclusive to `MathTransform​.getTargetDimensions()` exclusive.
    - The `dimensions` values shall be in strictly increasing order.
    - The `dimensions` values shall be greater than all values specified by all previous calls of this method since construction or since the last call to `clear()`.
    Parameters:
      `dimensions` - a sequence of target dimensions to keep, in strictly increasing order.
    Throws:
      `IllegalArgumentException` - if `dimensions` contains negative values or if values are not in a strictly increasing order.

  - ### addTargetDimensionRange

    public void addTargetDimensionRange(int lower, int upper) throws IllegalArgumentException
    Adds a range of output dimensions to keep in the separated transform. The `lower` and `upper` values define a range of target dimension indices of the transform given to the constructor.
    Parameters:
      `lower` - the lower dimension, inclusive. Shall not be smaller than 0.
      `upper` - the upper dimension, exclusive. Shall be smaller than `MathTransform​.getTargetDimensions()`.
    Throws:
      `IllegalArgumentException` - if `lower` or `upper` are out of bounds.

  - ### getTargetDimensions

    public int[] getTargetDimensions() throws IllegalStateException
    Returns the output dimensions to keep or kept in the separated transform. This method performs the first applicable action in the following list:
    1. Target dimensions have been explicitly set by at least one call to `addTargetDimensions(int...)` or `addTargetDimensionRange(int, int)` since construction or since last call to `clear()`. In such case, this method returns all specified target dimensions.
    2. No target dimensions were set but `separate()` has been invoked. In such case, the target dimensions are inferred automatically from the source dimensions and the transform.
    3. Otherwise an exception is thrown.
    Returns:
      the output dimension as a sequence of strictly increasing values.
    Throws:
      `IllegalStateException` - if output dimensions have not been set and `separate()` has not yet been invoked.

  - ### isSourceExpandable

    public boolean isSourceExpandable()
    Returns whether `separate()` is allowed to expand the list of source dimensions. The default value is `false`, which means that `separate()` either returns a `MathTransform` having exactly the requested source dimensions, or throws a `FactoryException`.
    Returns:
      whether `separate()` is allowed to add new source dimensions instead of throwing a `FactoryException`.
    Since:
      1.1

  - ### setSourceExpandable

    public void setSourceExpandable(boolean enabled)
    Sets whether `separate()` is allowed to expand the list of source dimensions. The default value is `false`, which means that `separate()` will throw a `FactoryException` if some target dimensions cannot be computed without inputs that are not in the list of source dimensions. If this flag is set to `true`, then `separate()` will be allowed to augment the list of source dimensions with any inputs that are essential for producing all requested outputs.
    Parameters:
      `enabled` - whether to allow source dimensions expansion.
    Since:
      1.1

  - ### separate

    public MathTransform separate() throws FactoryException
    Separates the math transform specified at construction time for given dimension indices. This method creates a math transform that use only the specified source dimensions and return only the specified target dimensions. If the source or target dimensions were not specified, then they will be inferred as below:
    - If source dimensions were unspecified, then the returned transform will keep only the source dimensions needed for computing the specified target dimensions. If all source dimensions need to be kept, then they should be specified explicitly.
    - If target dimensions were unspecified, then the returned transform will expect only the specified source dimensions as inputs, and the target dimensions will be inferred automatically.
    - If neither source and target positions were specified, then the returned transform will have the same set of target dimensions, but only the set of source dimensions required for computing those targets. In other words, this method drops unused source dimensions.
    The source and target dimensions actually used can be queried by calls to `getSourceDimensions()` or `getTargetDimensions()` after this `separate()` method.
    Returns:
      the separated math transform.
    Throws:
      `FactoryException` - if the transform cannot be separated.

  - ### replace

    public MathTransform replace(int lower, int upper, MathTransform replacement) throws FactoryException
    Replaces the transform in the given range of coordinate indexes. The coordinates at indexes in the range from `lower` inclusive to `upper` exclusive will be computed by the given `replacement`. Coordinates at other indexes are computed by the transform given at construction time.
    Parameters:
      `lower` - index of the first coordinate to compute with the given replacement.
      `upper` - index after the last coordinate to compute with the given replacement.
      `replacement` - the transform to use for the given range of coordinate indexes.
    Returns:
      a transform with the replacement, or the transform specified at construction time if no change.
    Throws:
      `FactoryException` - if the transform cannot be separated.
    Since:
      1.6

  - ### filterSourceDimensions

    protected MathTransform filterSourceDimensions(MathTransform step, int[] dimensions) throws FactoryException
    Creates a transform for the same mathematic as the given `step` but expecting only the given dimensions as inputs. This method is invoked by `separate()` when user-specified source dimensions need to be taken in account. The given `step` and `dimensions` are typically the values of `transform` and `sourceDimensions` fields respectively, but not necessarily. In particular those arguments will differ when this method is invoked recursively for processing concatenated or sub-transforms.

    Subclasses can override this method if they need to handle some `MathTransform` implementations in a special way. However, all implementations of this method shall obey to the following contract:

    - `sourceDimensions` and `targetDimensions` should not be assumed accurate since they may be temporarily outdated or modified during recursive calls to this method.
    - `sourceDimensions` should not be modified by this method.
    - `targetDimensions` must be overwritten (not updated) by this method to the sequence of all target dimensions of `step` that are also target dimensions of the returned transform. The indices shall be in strictly increasing order from 0 inclusive to `step​.getTargetDimensions()` exclusive.
    Parameters:
      `step` - the transform for which to retain only a subset of the source dimensions.
      `dimensions` - indices of the source dimensions of `step` to retain.
    Returns:
      a transform expecting only the given source dimensions.
    Throws:
      `FactoryException` - if the given transform is not separable.

  - ### filterTargetDimensions

    protected MathTransform filterTargetDimensions(MathTransform step, int[] dimensions) throws FactoryException
    Creates a transform for the same mathematic as the given `step` but producing only the given dimensions as outputs. This method is invoked by `separate()` when user-specified target dimensions need to be taken in account. The given `step` and `dimensions` are typically the values of `transform` and `targetDimensions` fields respectively, but not necessarily.

    Subclasses can override this method if they need to handle some `MathTransform` implementations in a special way. However, all implementations of this method shall obey to the following contract:

    - `sourceDimensions` and `targetDimensions` should not be assumed accurate.
    - `sourceDimensions` should not be modified by this method.
    - `targetDimensions` should not be modified by this method.
    The number and nature of inputs stay unchanged. For example if the supplied `transform` has (longitude, latitude, height) outputs, then a filtered transform may keep only the (longitude, latitude) part for the same inputs. In most cases, the filtered transform is non-invertible since it looses information.
    Parameters:
      `step` - the transform for which to retain only a subset of the target dimensions.
      `dimensions` - indices of the target dimensions of `step` to retain.
    Returns:
      a transform producing only the given target dimensions.
    Throws:
      `FactoryException` - if the given transform is not separable.