Class LoadSpatially

This strategy ensures that only the data within the visible extent of the Map is retrieved from the model. It can only be used on FeatureLayers whose model supports spatial queries. See Store.spatialQuery for more information about this capability. If you attempt to use this strategy with a model that does not support spatial queries, an error will be thrown.

Additionally, you can configure a QueryProvider on this loading strategy to further refine the amount of data to load from the FeatureModel.

Note: QueryProvider can define a WFS query object using the WFSQueryOptions.maxFeatures property. For a given visible extent of the Map, this property limits the maximum number of features to load. When this happens, the LoadSpatially strategy will re-query when zooming in or out, so that a new set of data is retrieved for the new view extent.

In a 3D scene, the visible extent of the Map may cover multiple areas at different scales. For example, when the camera is tilted, data near the horizon is visualized at a lower scale than data closer to the camera. To handle this, LuciadRIA divides the map into multiple zones that correspond with scale levels that are defined by the QueryProvider. The loading strategy queries the model by passing the bounds and the query object for each visible scale level zone, and combines the data across zones for consistent visualization. This approach enables visualization of large datasets in 3D, while still allowing you to apply data-specific business rules when loading and rendering. Please note that you can suppress this behavior by setting LoadSpatiallyStrategyConstructorOptions.singleQueryLevel to true.

To fully benefit from this loading capability, the QueryProvider should define scale levels and associated query objects, allowing you to limit the number of features at smaller scales, or to prevent loading data entirely at the least detailed level (level 0) using QueryProvider.QUERY_NONE. You can also define the layer’s minimum and maximum scale at which features should be rendered. LuciadRIA will query the model using bounds computed for the area within these scale limits.

Note: Selected features are preserved between queries and are not removed from the model when new data is returned, provided that the features returned by the query have stable, fixed IDs. If feature IDs change between queries, selections may be lost.

  const townQueryFilter = {
    filter: eq(property("class"), literal("town"))
  };

  class CityQueryProvider extends QueryProvider {
    getQueryForLevel(level: number) {
      // no data requested for least detailed level
      if (level === 0) {
        return QueryProvider.QUERY_NONE;
      }
      // data matching the specific filter is only loaded
      if (level === 1) {
        return townQueryFilter;
      }
      // everything is loaded otherwise
      return null;
    }

    // The query provider defines 3 scale levels:
    // The scale level 0 denotes an area with scales smaller than 1 / 50000,
    // The scale level 1 that represents area with scales between than 1 / 50000 and 1 / 1000,
    // The scale level 2 that represents area with scales greater than 1 / 1000 (closer to the observer).
    getQueryLevelScales(layer?: FeatureLayer, map?: RIAMap) {
      return [ 1/50000, 1/1000 ];
    }
  }

  // the cityModel must support spatial queries
  const cityLayer = new FeatureLayer(cityModel, {
    loadingStrategy: new LoadSpatially({queryProvider: new CityQueryProvider()})
  });
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