public int countImagesInSector(Sector sector, int levelNumber) {
    if (sector == null) {
      String msg = Logging.getMessage("nullValue.SectorIsNull");
      Logging.logger().severe(msg);
      throw new IllegalArgumentException(msg);
    }

    Level targetLevel = this.levels.getLastLevel();
    if (levelNumber >= 0) {
      for (int i = levelNumber; i < this.getLevels().getLastLevel().getLevelNumber(); i++) {
        if (this.levels.isLevelEmpty(i)) continue;

        targetLevel = this.levels.getLevel(i);
        break;
      }
    }

    // Collect all the tiles intersecting the input sector.
    LatLon delta = targetLevel.getTileDelta();
    Angle latOrigin = this.levels.getTileOrigin().getLatitude();
    Angle lonOrigin = this.levels.getTileOrigin().getLongitude();
    final int nwRow = Tile.computeRow(delta.getLatitude(), sector.getMaxLatitude(), latOrigin);
    final int nwCol = Tile.computeColumn(delta.getLongitude(), sector.getMinLongitude(), lonOrigin);
    final int seRow = Tile.computeRow(delta.getLatitude(), sector.getMinLatitude(), latOrigin);
    final int seCol = Tile.computeColumn(delta.getLongitude(), sector.getMaxLongitude(), lonOrigin);

    int numRows = nwRow - seRow + 1;
    int numCols = seCol - nwCol + 1;

    return numRows * numCols;
  }
  private MercatorTextureTile[][] getTilesInSector(Sector sector, int levelNumber) {
    if (sector == null) {
      String msg = Logging.getMessage("nullValue.SectorIsNull");
      Logging.logger().severe(msg);
      throw new IllegalArgumentException(msg);
    }

    Level targetLevel = this.levels.getLastLevel();
    if (levelNumber >= 0) {
      for (int i = levelNumber; i < this.getLevels().getLastLevel().getLevelNumber(); i++) {
        if (this.levels.isLevelEmpty(i)) continue;

        targetLevel = this.levels.getLevel(i);
        break;
      }
    }

    // Collect all the tiles intersecting the input sector.
    LatLon delta = targetLevel.getTileDelta();
    Angle latOrigin = this.levels.getTileOrigin().getLatitude();
    Angle lonOrigin = this.levels.getTileOrigin().getLongitude();
    final int nwRow = Tile.computeRow(delta.getLatitude(), sector.getMaxLatitude(), latOrigin);
    final int nwCol = Tile.computeColumn(delta.getLongitude(), sector.getMinLongitude(), lonOrigin);
    final int seRow = Tile.computeRow(delta.getLatitude(), sector.getMinLatitude(), latOrigin);
    final int seCol = Tile.computeColumn(delta.getLongitude(), sector.getMaxLongitude(), lonOrigin);

    int numRows = nwRow - seRow + 1;
    int numCols = seCol - nwCol + 1;
    MercatorTextureTile[][] sectorTiles = new MercatorTextureTile[numRows][numCols];

    for (int row = nwRow; row >= seRow; row--) {
      for (int col = nwCol; col <= seCol; col++) {
        TileKey key =
            new TileKey(targetLevel.getLevelNumber(), row, col, targetLevel.getCacheName());
        Sector tileSector = this.levels.computeSectorForKey(key);
        MercatorSector mSector = MercatorSector.fromSector(tileSector); // TODO: check
        sectorTiles[nwRow - row][col - nwCol] =
            new MercatorTextureTile(mSector, targetLevel, row, col);
      }
    }

    return sectorTiles;
  }
  private void createTopLevelTiles() {
    MercatorSector sector = (MercatorSector) this.levels.getSector();

    Level level = levels.getFirstLevel();
    Angle dLat = level.getTileDelta().getLatitude();
    Angle dLon = level.getTileDelta().getLongitude();

    Angle latOrigin = this.levels.getTileOrigin().getLatitude();
    Angle lonOrigin = this.levels.getTileOrigin().getLongitude();

    // Determine the row and column offset from the common World Wind global tiling origin.
    int firstRow = Tile.computeRow(dLat, sector.getMinLatitude(), latOrigin);
    int firstCol = Tile.computeColumn(dLon, sector.getMinLongitude(), lonOrigin);
    int lastRow = Tile.computeRow(dLat, sector.getMaxLatitude(), latOrigin);
    int lastCol = Tile.computeColumn(dLon, sector.getMaxLongitude(), lonOrigin);

    int nLatTiles = lastRow - firstRow + 1;
    int nLonTiles = lastCol - firstCol + 1;

    this.topLevels = new ArrayList<MercatorTextureTile>(nLatTiles * nLonTiles);

    // Angle p1 = Tile.computeRowLatitude(firstRow, dLat);
    double deltaLat = dLat.degrees / 90;
    double d1 = -1.0 + deltaLat * firstRow;
    for (int row = firstRow; row <= lastRow; row++) {
      // Angle p2;
      // p2 = p1.add(dLat);
      double d2 = d1 + deltaLat;

      Angle t1 = Tile.computeColumnLongitude(firstCol, dLon, lonOrigin);
      for (int col = firstCol; col <= lastCol; col++) {
        Angle t2;
        t2 = t1.add(dLon);

        this.topLevels.add(
            new MercatorTextureTile(new MercatorSector(d1, d2, t1, t2), level, row, col));
        t1 = t2;
      }
      d1 = d2;
    }
  }