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.
Example: a collection of Grid­Coverage instances may 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.
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

Defined in the sis-storage module

  • Constructor Details

    • CoverageAggregator

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

  • Method Details

    • 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.
      Parameters:
      resources - resources to add.
      Throws:
      Data­Store­Exception - if a resource cannot be used.

    • 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.
      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.

    • 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). Consequently, this method should usually 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.
      Parameters:
      strategy - new algorithm to apply for merging source coverages at the same grid index, or null if none.

    • build

      public Resource build()
      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 prevent the concatenation of all coverages in a single resource.

      This method is not thread safe. If the add(…) and add­All(…) methods were invoked in background threads, then all additions must be finished before this method is invoked.

      Returns:
      the aggregation or concatenation of all components added to this aggregator.

    • toString

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