Module org.apache.sis.storage
Package org.apache.sis.storage.aggregate

Class CoverageAggregator

Object
CoverageAggregator
public final class CoverageAggregator extends Object
Creates a grid coverage resource from an aggregation of an arbitrary number of other resources. This class accepts heterogeneous resources (a data lake), organizes them in a tree of resources as described in the next section, then performs different kinds of aggregation:
  • Creation of a data cube from a collection of slices: If a collection of Grid­Coverage­Resource instances represent the same phenomenon (for example Sea Surface Temperature) over the same geographic area but at different dates and times. Coverage­Aggregator can be used for building a single data cube with a time axis.
  • Aggregation of bands: Resources having different sample dimensions can be combined in a single resource.

Generated resource tree

All source coverages should share the same CRS and have the same ranges (sample dimensions). If this is not the case, then the source coverages will be grouped in different aggregates with an uniform CRS and set of ranges in each sub-aggregates. More specifically, Coverage­Aggregator organizes resources as below, except that parent nodes having only one child are omitted: 
     Root aggregate
     ├─ All coverages with same sample dimensions #1
     │  └─ ...
     └─ All coverages with same sample dimensions #2
        ├─ Coverages with equivalent reference systems #1
        │  └─ ...
        └─ Coverages with equivalent reference systems #2
           ├─ Slices with compatible "grid to CRS" #1
           ├─ Slices with compatible "grid to CRS" #2
           └─ ...
Where:
  • Equivalent reference systems means two Coordinate­Reference­System instances for which Utilities​.equals­Ignore­Metadata(Object, Object) returns true.
  • Compatible grid to CRS means two grid to CRS transforms which are identical (with small tolerance for rounding errors) except for the translation terms, with the additional condition that the translations, when expressed in units of grid cell indices, can differ only by integer amounts of cells.
  • Slices means source coverages declared to this aggregator by calls to add(…) methods, after they have been incorporated in a data cube by this aggregator. Above tree does not contain the individual slices, but data cubes containing all slices that can fit.

Multi-threading and concurrency

All add(…) methods can be invoked concurrently from arbitrary threads. It is okay to load Grid­Coverage­Resource instances in parallel threads and add those resources to Coverage­Aggregator without synchronization. However, the final build() method is not thread-safe; that method shall be invoked from a single thread after all sources have been added and no more addition are in progress.
Since:
1.3

  • Constructor Details

    • CoverageAggregator

      public CoverageAggregator()
      Creates an initially empty aggregator with no listeners.
      Since:
      1.4

    • CoverageAggregator

      public CoverageAggregator(StoreListeners listeners)
      Creates an initially empty aggregator with the given listeners.
      Parameters:
      listeners - listeners of the parent resource, or null if none. This is usually the listeners of the Data­Store.

  • Method Details

    • add

      public void add(GridCoverage coverage)
      Adds the given coverage. This method can be invoked from any thread.
      Parameters:
      coverage - coverage to add.
      Since:
      1.4

    • add

      public void add(GridCoverageResource resource) throws DataStoreException
      Adds the given resource. This method can be invoked from any thread. This method does not recursively decomposes an Aggregate into its component. If such decomposition is desired, see add­Components(Aggregate) instead.
      Parameters:
      resource - resource to add.
      Throws:
      Data­Store­Exception - if the resource cannot be used.

    • addComponents

      public void addComponents(Aggregate resource) throws DataStoreException
      Adds all components of the given aggregate. This method can be invoked from any thread. It delegates to add(Grid­Coverage­Resource) for each component in the aggregate which is an instance of Grid­Coverage­Resource. Components that are themselves instance of Aggregate are decomposed recursively.
      Parameters:
      resource - resource to add.
      Throws:
      Data­Store­Exception - if a component of the resource cannot be used.
      "TODO:"
      Instead of ignoring non-coverage instances, we should put them in a separated aggregate.

    • addAll

      public void addAll(Stream<? extends GridCoverageResource> resources) throws DataStoreException
      Adds all grid resources provided by the given stream. This method can be invoked from any thread. It delegates to add(Grid­Coverage­Resource) for each element in the stream. Aggregate instances are added as-is (not decomposed in their components).
      Parameters:
      resources - resources to add.
      Throws:
      Data­Store­Exception - if a resource cannot be used.
      See Also:

    • addRangeAggregate

      public void addRangeAggregate(GridCoverageResource... sources) throws DataStoreException
      Adds a resource whose range is the aggregation of the ranges of a sequence of resources. This method combines homogeneous grid coverage resources by "stacking" their sample dimensions (bands). The grid geometry is typically the same for all resources, but some variations described below are allowed. The number of sample dimensions in the aggregated coverage is the sum of the number of sample dimensions in each individual resource.

      This convenience method delegates to add­Range­Aggregate(Grid­Coverage­Resource[], int[][]). See that method for more information on restrictions.

      Parameters:
      sources - resources whose bands shall be aggregated, in order.
      Throws:
      Data­Store­Exception - if an error occurred while fetching the grid geometry or sample dimensions from a resource.
      Illegal­Grid­Geometry­Exception - if a grid geometry is not compatible with the others.
      Since:
      1.4
      See Also:

    • addRangeAggregate

      public void addRangeAggregate(GridCoverageResource[] sources, int[][] bandsPerSource) throws DataStoreException
      Adds a resource whose range is the aggregation of the specified bands of a sequence of resources. This method performs the same work than add­Range­Aggregate(Grid­Coverage­Resource...), but with the possibility to specify the sample dimensions to retain in each source coverage. The bands­Per­Source argument specifies the sample dimensions to keep, in order. That array can be null for selecting all sample dimensions in all source coverages, or may contain null elements for selecting all sample dimensions of the corresponding coverage. An empty array element (i.e. zero sample dimension to select) discards the corresponding source coverage.

      Restrictions

      • All resources shall use the same coordinate reference system (CRS).
      • All resources shall have the same domain, except for the grid extent and the translation terms which can vary by integer numbers of grid cells.
      • All grid extents shall intersect and the intersection area shall be non-empty.
      • If coverage data are stored in Rendered­Image instances, then all images shall use the same data type.
      Some of those restrictions may be relaxed in future Apache SIS versions.
      Parameters:
      sources - resources whose bands shall be aggregated, in order.
      bands­Per­Source - sample dimensions for each source. May be null or may contain null elements.
      Throws:
      Data­Store­Exception - if an error occurred while fetching the grid geometry or sample dimensions from a resource.
      Illegal­Grid­Geometry­Exception - if a grid geometry is not compatible with the others.
      Illegal­Argument­Exception - if some band indices are duplicated or outside their range of validity.
      Since:
      1.4
      See Also:

    • getColorizer

      public Colorizer getColorizer()
      Returns the colorization algorithm to apply on computed images. This algorithm is used for all resources added by add­Range­Aggregate(Grid­Coverage­Resource[], int[][]),
      Returns:
      colorization algorithm to apply on computed image, or null for default.
      Since:
      1.4

    • setColorizer

      public void setColorizer(Colorizer colorizer)
      Sets the colorization algorithm to apply on computed images. This algorithm applies to all resources added by add­Range­Aggregate(Grid­Coverage­Resource[], int[][]), including resources already added before this method is invoked. If this method is never invoked, the default value is null.
      Parameters:
      colorizer - colorization algorithm to apply on computed image, or null for default.
      Since:
      1.4

    • getMergeStrategy

      public MergeStrategy getMergeStrategy()
      Returns the algorithm to apply when more than one grid coverage can be found at the same grid index. This is the most recent value set by a call to set­Merge­Strategy(Merge­Strategy), or null if no strategy has been specified. In the latter case, a Subspace­Not­Specified­Exception will be thrown by Grid­Coverage​.render(Grid­Extent) if more than one source coverage (slice) is found for a specified grid index.
      Returns:
      algorithm to apply for merging source coverages at the same grid index, or null if none.

    • setMergeStrategy

      public void setMergeStrategy(MergeStrategy strategy)
      Sets the algorithm to apply when more than one grid coverage can be found at the same grid index. The new strategy applies to the next coverages to be added; previously added coverage may or may not be impacted by this change (see below). For avoiding hard-to-predict behavior, this method should be invoked before to add the first coverage.

      Effect on previously added coverages

      The merge strategy of previously added coverages is not modified by this method call, except for coverages (slices) that become part of the same aggregated Grid­Coverage­Resource (data cube) than a coverage added after this method call. In such case, the strategy set by this call to set­Merge­Strategy(…) prevails. Said otherwise, the merge strategy of a data cube is the strategy which was active at the time of the most recently added slice for that data cube.
      Parameters:
      strategy - new algorithm to apply for merging source coverages at the same grid index, or null if none.

    • build

      public Resource build(GenericName identifier)
      Builds a resource which is the aggregation or concatenation of all components added to this aggregator. The returned resource will be an instance of Grid­Coverage­Resource if possible, or an instance of Aggregate if some heterogeneity in grid geometries or sample dimensions prevents the concatenation of all coverages in a single resource.

      An identifier can optionally be specified for the resource. This identifier will be used if this method creates an aggregated or concatenated resource, but it will be ignored if this method returns directly one of the resource specified to the add(…) methods.

      Multi-threading

      If the add(…) and add­All(…) methods were invoked in background threads, then all additions must be finished before this method is invoked.
      Parameters:
      identifier - identifier to assign to the aggregated resource, or null if none.
      Returns:
      the aggregation or concatenation of all components added to this aggregator.
      Since:
      1.4

    • build

      @Deprecated public Resource build()
      Deprecated.
      Replaced by build(Generic­Name).

    • toString

      public String toString()
      Returns a string representation for debugging purposes.
      Overrides:
      to­String in class Object