Package com.luciad.models.features

Interface IFeatureModel

All Superinterfaces:
Model
public interface IFeatureModel extends Model
A feature model allows to uniformly access vector data.

See article for more details on how to use and how to implement this class.

Using a model

A user of a model:

  • Can use the query method on any thread
  • Can expect model change events on any thread. This means that the user of a model is responsible for creating a thread-safe observer implementation, and for possible rescheduling of the model events on a different thread if needed.

Implementing a model

The model implementation has multiple responsibilities.

  • Access the data uniformly. I.e. translate data storage entries into Feature instances.
  • Filter the data. When a user of the model queries the model, he can specify a filter. The model implementation must make sure that data is correctly filtered, as efficiently as possible.
  • All model implementations must be thread safe for reading, to allow multiples queries in parallel.
  • Make sure dynamic data (i.e. data that changes over time) is updated in a thread-safe way.
  • Make sure that notifications are sent when dynamic data changes.
  • Make sure that the data is presented in a consistent way. That is, after the model sends out a change event for a Feature, the query() method must also reflect that change. This can be guaranteed by making sure that model updates (internal updates + firing model change notifications) and calls to the query method are never executed simultaneously. Notifications must not be sent while the query() method is executing.

Persisting changes

Feature models can add support for persisting model changes. See this article for more information.

Performance considerations

In order to optimize feature loading, it is recommended to follow these rules when creating a model:

  • The model should have bounds.
  • The features should contain a property whose value is a geometry.
  • Feature data types should have a GeometryDataAnnotation.
  • The reference used should not be geocentric.

  • Method Details

    • query

      void query(@NotNull FeatureQuery query, @NotNull IFeatureQueryCallback callback)
      Queries the model, and passes the result to the given callback.

      The callback can return false to indicate that the query can stop. This method passes Feature instances to the given callback. These instances contain a copy of the original data (structured according to the DataModel of this model). The ownership of these features is passed to the caller of this method (through the callback). This means that the model is not allowed to modify/deleted these Feature instances, once they are passed to the callback function.

      This method is thread-safe, and can be called on any thread.

      This method is synchronous and blocking. In other words, as soon as this function returns

      • the given callback must have been called for each resulting feature
      • no more calls to the callback can be done anymore

      Implementations of this method have the responsibilities described in the class documentation.

      When implementing this method you may want to use the existing evaluation support which you can find in FeatureExpressionEvaluator and FeatureExpressionEvaluatorFactory.

      Example to query the model for a Feature with a specific id. 

          FeatureQuery query = FeatureQuery.newBuilder().featureIds(List.of(featureId)).build();
    model.query(query, feature -> {
      System.out.println(feature.getId());
      return false;
    });
      Parameters:
      query - the query
      callback - a callback which can handle the result of the query operation

    • addObserver

      void addObserver(@NotNull IFeatureModelObserver modelObserver) throws IllegalArgumentException
      Adds an observer that allows to receive change events from this feature model.

      Adding the same observer twice is forbidden, and will cause an exception to be thrown.

      Parameters:
      modelObserver - an observer
      Throws:
      IllegalArgumentException - when the observer was already added.

    • removeObserver

      void removeObserver(@NotNull IFeatureModelObserver modelObserver) throws IllegalArgumentException
      Removes the given observer.

      If the given observer was never added, an exception is thrown.

      Parameters:
      modelObserver - an observer
      Throws:
      IllegalArgumentException - when the observer is not known.

    • getFeatureModelMetadata

      @NotNull FeatureModelMetadata getFeatureModelMetadata()
      Returns the feature model meta data.

      It provides information about the types of features one can expect within the model.

      Returns:
      the feature model meta data.

    • getUpdater

      @Nullable IFeatureModelUpdater getUpdater()
      Returns the IFeatureModelUpdater that is used to make changes to the model.

      When a model can't be updated, null must be returned.

      Typically, IFeatureModel implementations implement these changes as in-memory changes. FeatureModelPersistenceManager can then be used to persist those changes (if persisting changes is supported). An IFeatureModel can however choose to immediately persist any of these changes immediately, if persisting changes doesn't imply a large performance overhead for example. In that case a FeatureModelPersistenceManager is not needed, and getPersistenceManager must return null.

      Returns:
      the updater that can be used for this model.

    • getPersistenceManager

      @Nullable FeatureModelPersistenceManager getPersistenceManager()
      Returns the FeatureModelPersistenceManager that is used to persist in-memory changes made through IFeatureModelUpdater.

      When a model doesn't support (or doesn't need) saving functionality, null must be returned.

      If persisting changes is not supported by the model, or if it is not needed because IFeatureModelUpdater already automatically persists its changes, this method must return null.

      Returns:
      the FeatureModelPersistenceManager that can be used for this model.
      Since:
      2023.1