Method visibleSources

modules/core/ImagerySystem.js:336–371

* visibleSources * Returns array of known imagery sources that are valid at the given extent and zoom * @return Array

()

   *  @return  Array
   */
  visibleSources() {
    if (!this._imageryIndex) return [];   // called before init()?

    const context = this.context;
    const viewport = context.viewport;
    const extent = viewport.visibleExtent();
    const zoom = viewport.transform.zoom;

    const visible = new Set();
    (this._imageryIndex.query.bbox(extent.rectangle(), true) || [])
      .forEach(d => visible.add(d.id));

    const currSource = this._baseLayer;
    const sources = [...this._imageryIndex.sources.values()];

    // Recheck blocked sources only if we detect new blocklists pulled from the OSM API.
    const osm = context.services.osm;
    const blocklists = osm?.imageryBlocklists ?? [];
    const blocklistChanged = (blocklists.length !== this._checkedBlocklists.length) ||
      blocklists.some((regex, index) => String(regex) !== this._checkedBlocklists[index]);

    if (blocklistChanged) {
      for (const source of sources) {
        source.isBlocked = blocklists.some(regex => regex.test(source.template));
      }
      this._checkedBlocklists = blocklists.map(regex => String(regex));
    }

    return sources.filter(source => {
      if (currSource === source) return true;  // always include the current imagery
      if (source.isBlocked) return false;      // even bundled sources may be blocked - iD#7905
      if (!source.polygon) return true;        // always include imagery with worldwide coverage
      if (zoom && zoom < 6) return false;      // optionally exclude local imagery at low zooms
      return visible.has(source.id);           // include imagery visible in given extent
    });
  }


  /**