# Class GridCoverage

Object
BandedCoverage
GridCoverage

Direct Known Subclasses:
  `BufferedGridCoverage`, `GridCoverage2D`

public abstract class GridCoverage extends BandedCoverage
Base class of coverages with domains defined as a set of grid points. The essential property of coverage is to be able to generate a value for any point within its domain. Since a grid coverage is represented by a grid of values, the value returned by the coverage for a point is that of the grid value whose location is nearest the point.

Since:
  1.0

- ## Nested Class Summary

  Nested Classes
  Modifier and Type
  Class
  Description
  `static interface`
  `GridCoverage​.Evaluator`
  Interpolates values of sample dimensions at given positions.

- ## Field Summary

  Fields
  Modifier and Type
  Field
  Description
  `protected final GridGeometry`
  `gridGeometry`
  The grid extent, coordinate reference system (CRS) and conversion from cell indices to CRS.

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `GridCoverage(GridGeometry domain, List<? extends SampleDimension> ranges)`
  Constructs a grid coverage using the specified grid geometry and sample dimensions.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `protected GridCoverage`
  `createConvertedValues(boolean converted)`
  Creates the grid coverage instance for the converted or packed values.
  `GridCoverage​.Evaluator`
  `evaluator()`
  Creates a new function for computing or interpolating sample values at given locations.
  `GridCoverage`
  `forConvertedValues(boolean converted)`
  Returns a grid coverage that contains real values or sample values, depending if `converted` is `true` or `false` respectively.
  `CoordinateReferenceSystem`
  `getCoordinateReferenceSystem()`
  Returns the coordinate reference system to which the values in grid domain are referenced.
  `Optional<Envelope>`
  `getEnvelope()`
  Returns the bounding box for the coverage domain in CRS coordinates.
  `GridGeometry`
  `getGridGeometry()`
  Returns information about the domain of this grid coverage.
  `List<SampleDimension>`
  `getSampleDimensions()`
  Returns information about the range of this grid coverage.
  `abstract RenderedImage`
  `render(GridExtent sliceExtent)`
  Returns a two-dimensional slice of grid data as a rendered image.
  `String`
  `toString()`
  Returns a string representation of this grid coverage for debugging purpose.
  `TreeTable`
  `toTree(Locale locale, int bitmask)`
  Returns a tree representation of some elements of this grid coverage.

  ### Methods inherited from class Object

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

- ## Field Details

  - ### gridGeometry

    protected final GridGeometry gridGeometry
    The grid extent, coordinate reference system (CRS) and conversion from cell indices to CRS.
    See Also:
      - `getGridGeometry()`

- ## Constructor Details

  - ### GridCoverage

    protected GridCoverage(GridGeometry domain, List<? extends SampleDimension> ranges)
    Constructs a grid coverage using the specified grid geometry and sample dimensions. The grid geometry defines the "domain" (inputs) of the coverage function, and the sample dimensions define the "range" (output) of that function.
    Parameters:
      `domain` - the grid extent, CRS and conversion from cell indices to CRS.
      `ranges` - sample dimensions for each image band.
    Throws:
      `NullPointerException` - if an argument is `null` or if the list contains a null element.
      `IllegalArgumentException` - if the `range` list is empty.

- ## Method Details

  - ### getCoordinateReferenceSystem

    public CoordinateReferenceSystem getCoordinateReferenceSystem()
    Returns the coordinate reference system to which the values in grid domain are referenced. This is the target coordinate reference system of the `gridToCRS` math transform.

    The default implementation delegates to `GridGeometry​.getCoordinateReferenceSystem()`.

    Specified by:
      `getCoordinateReferenceSystem` in class `BandedCoverage`
    Returns:
      the "real world" CRS of this coverage.
    Throws:
      `IncompleteGridGeometryException` - if the grid geometry has no CRS.

  - ### getEnvelope

    public Optional<Envelope> getEnvelope()
    Returns the bounding box for the coverage domain in CRS coordinates. The envelope encompasses all cell surfaces, from the left border of leftmost cell to the right border of the rightmost cell and similarly along other axes.

    The default implementation delegates to `GridGeometry​.getEnvelope()`.

    Specified by:
      `getEnvelope` in class `BandedCoverage`
    Returns:
      the bounding box for the coverage domain in CRS coordinates.
    Since:
      1.2

  - ### getGridGeometry

    public GridGeometry getGridGeometry()
    Returns information about the domain of this grid coverage. Information includes the grid extent, CRS and conversion from cell indices to CRS. `GridGeometry` can also provide derived information like bounding box and resolution.
    Returns:
      grid extent, CRS and conversion from cell indices to CRS.
    See Also:
      - `GridCoverageResource​.getGridGeometry()`

  - ### getSampleDimensions

    public List<SampleDimension> getSampleDimensions()
    Returns information about the range of this grid coverage. Information include names, sample value ranges, fill values and transfer functions for all bands in this grid coverage. The length of the returned list should be equal to the number of bands in the rendered image.
    Specified by:
      `getSampleDimensions` in class `BandedCoverage`
    Returns:
      names, value ranges, fill values and transfer functions for all bands in this grid coverage.
    See Also:
      - `GridCoverageResource​.getSampleDimensions()`

  - ### forConvertedValues

    public GridCoverage forConvertedValues(boolean converted)
    Returns a grid coverage that contains real values or sample values, depending if `converted` is `true` or `false` respectively. If there is no transfer function defined by the sample dimensions, then this method returns `this`. In all cases, the returned grid coverage r has the following properties:
    - The list returned by `r​.getSampleDimensions()` is equal to the list returned by `this.getSampleDimensions()` with each element e replaced by `e.forConvertedValues(converted)`.
    - The `RenderedImage` produced by `r​.render(extent)` is equivalent to the image returned by `this.render(extent)` with all sample values converted using the transfer function if `converted` is `true`, or the inverse of transfer function if `converted` is `false`.
    The default implementation delegates to `createConvertedValues(boolean)` when first needed, then caches the result for future invocations.
    Parameters:
      `converted` - `true` for a coverage containing converted values, or `false` for a coverage containing packed values.
    Returns:
      a coverage containing converted or packed values, depending on `converted` argument value. May be `this` but never `null`.
    Throws:
      `CannotEvaluateException` - if an error occurred while conversion the values.
    See Also:
      - `SampleDimension​.forConvertedValues(boolean)`

  - ### createConvertedValues

    protected GridCoverage createConvertedValues(boolean converted)
    Creates the grid coverage instance for the converted or packed values. This method is invoked by `forConvertedValues(boolean)` when first needed. Then the result returned by this method is cached for future invocations of `forConvertedValues(converted)`.

    Subclasses can override this method for customizing the converted coverages while leverage the caching done by `forConvertedValues(boolean)`.

    Parameters:
      `converted` - `true` for a coverage containing converted values, or `false` for a coverage containing packed values.
    Returns:
      a new coverage containing converted or packed values, depending on `converted` argument value. May be `this` but never `null`.
    Throws:
      `CannotEvaluateException` - if an error occurred while conversion the values.
    Since:
      1.3

  - ### evaluator

    public GridCoverage.Evaluator evaluator()
    Creates a new function for computing or interpolating sample values at given locations. That function accepts `DirectPosition` in arbitrary Coordinate Reference System; conversions to grid indices are applied as needed.

    #### Multi-threading

    `Evaluator`s are not thread-safe. For computing sample values concurrently, a new `Evaluator` instance should be created for each thread by invoking this method multiple times.
    Specified by:
      `evaluator` in class `BandedCoverage`
    Returns:
      a new function for computing or interpolating sample values.
    Since:
      1.1

  - ### render

    public abstract RenderedImage render(GridExtent sliceExtent)
    Returns a two-dimensional slice of grid data as a rendered image. The given `sliceExtent` argument specifies the coordinates of the slice in all dimensions that are not in the two-dimensional image. For example if this grid coverage has (x,y,z,t) dimensions and we want to render an image of data in the (x,y) dimensions, then the given `sliceExtent` shall contain the (z,t) coordinates of the desired slice. Those coordinates are specified in a grid extent where low coordinate = high coordinate in the z and t dimensions. The two dimensions of the data to be shown (x and y in our example) shall be the only dimensions having a size greater than 1 cell.

    If the `sliceExtent` argument is `null`, then the default value is `getGridGeometry().getExtent()`. This means that `gridExtent` is optional for two-dimensional grid coverages or grid coverages where all dimensions except two have a size of 1 cell. If the grid extent contains more than 2 dimensions with a size greater than one cell, then a `SubspaceNotSpecifiedException` is thrown.

    #### How to compute a slice extent from a slice point in "real world" coordinates

    The `sliceExtent` is specified to this method as grid indices. If the z and t values are not grid indices but are relative to some Coordinate Reference System (CRS) instead, then the slice extent can be computed as below. First, a slice point containing the z and t coordinates should be constructed as a `DirectPosition` in one of the following ways:
    - The `slicePoint` has a CRS with two dimensions less than this grid coverage CRS.
    - The `slicePoint` has the same CRS as this grid coverage, but the two coordinates to exclude are set to `Double​.NaN`.
    Then:

        sliceExtent = getGridGeometry().derive().slice(slicePoint).getIntersection();

    If the `slicePoint` CRS is different than this grid coverage CRS (except for the number of dimensions), a coordinate transformation will be applied as needed.

    #### Characteristics of the returned image

    Image dimensions x and y map to the first and second dimension respectively of the two-dimensional `sliceExtent` subspace. The coordinates given by `RenderedImage​.getMinX()` and `getMinY()` will be the image location relative to the location specified in `sliceExtent` low coordinates. For example, in the case of image minimum X coordinate:
    - A value of 0 means that the image left border is exactly where requested by `sliceExtent​.getLow(xDimension)`.
    - A positive value means that the returned image is shifted to the right compared to specified extent. This implies that the image has less data than requested on left side. It may happen if the specified extent is partially outside grid coverage extent.
    - A negative value means that the returned image is shifted to the left compared to specified extent. This implies that the image has more data than requested on left side. It may happen if the image is tiled, the specified `sliceExtent` covers many tiles, and expanding the specified extent is necessary for returning an integer number of tiles.
    Similar discussion applies to the minimum Y coordinate. The image width and height will be the `sliceExtent` sizes if this method can honor exactly the request, or otherwise may be adjusted for the same reasons as x and y location discussed above.

    Implementations should return a view as much as possible, without copying sample values. `GridCoverage` subclasses can use the `ImageRenderer` class as a helper tool for that purpose. This method does not mandate any behavior regarding tiling (size of tiles, their numbering system, etc.). Some implementations may defer data loading until a tile is requested.

    Parameters:
      `sliceExtent` - a subspace of this grid coverage where all dimensions except two have a size of 1 cell. May be `null` if this grid coverage has only two dimensions with a size greater than 1 cell.
    Returns:
      the grid slice as a rendered image. Image location is relative to `sliceExtent`.
    Throws:
      `MismatchedDimensionException` - if the given extent does not have the same number of dimensions as this coverage.
      `SubspaceNotSpecifiedException` - if the given argument is not sufficient for reducing the grid to a two-dimensional slice.
      `DisjointExtentException` - if the given extent does not intersect this grid coverage.
      `CannotEvaluateException` - if this method cannot produce the rendered image for another reason.

  - ### toString

    public String toString()
    Returns a string representation of this grid coverage for debugging purpose. The returned string is implementation dependent and may change in any future version. Current implementation is equivalent to the following, where `<default flags>` is the same set of flags than `GridGeometry​.toString()`.

        return toTree(Locale.getDefault(), <default flags>).toString();

    Overrides:
      `toString` in class `Object`
    Returns:
      a string representation of this grid coverage for debugging purpose.

  - ### toTree

    @Debug public TreeTable toTree(Locale locale, int bitmask)
    Returns a tree representation of some elements of this grid coverage. The tree representation is for debugging purpose only and may change in any future SIS version.
    Parameters:
      `locale` - the locale to use for textual labels.
      `bitmask` - combination of `GridGeometry` flags.
    Returns:
      a tree representation of the specified elements.
    See Also:
      - `GridGeometry​.toTree(Locale, int)`