private boolean atMaxLevel(DrawContext dc) {
    Position vpc = dc.getViewportCenterPosition();
    if (dc.getView() == null || this.getLevels() == null || vpc == null) return false;

    if (!this.getLevels().getSector().contains(vpc.getLatitude(), vpc.getLongitude())) return true;

    Level nextToLast = this.getLevels().getNextToLastLevel();
    if (nextToLast == null) return true;

    Sector centerSector =
        nextToLast.computeSectorForPosition(
            vpc.getLatitude(), vpc.getLongitude(), this.getLevels().getTileOrigin());
    return this.needToSplit(dc, centerSector);
  }
  protected static boolean isTileVisible(
      DrawContext dc, Tile tile, double minDistanceSquared, double maxDistanceSquared) {
    if (!tile.getSector().intersects(dc.getVisibleSector())) return false;

    View view = dc.getView();
    Position eyePos = view.getEyePosition();
    if (eyePos == null) return false;

    Angle lat =
        clampAngle(
            eyePos.getLatitude(),
            tile.getSector().getMinLatitude(),
            tile.getSector().getMaxLatitude());
    Angle lon =
        clampAngle(
            eyePos.getLongitude(),
            tile.getSector().getMinLongitude(),
            tile.getSector().getMaxLongitude());
    Vec4 p = dc.getGlobe().computePointFromPosition(lat, lon, 0d);
    double distSquared = dc.getView().getEyePoint().distanceToSquared3(p);
    //noinspection RedundantIfStatement
    if (minDistanceSquared > distSquared || maxDistanceSquared < distSquared) return false;

    return true;
  }
  protected static boolean isNameVisible(
      DrawContext dc, PlaceNameService service, Position namePosition) {
    double elevation = dc.getVerticalExaggeration() * namePosition.getElevation();
    Vec4 namePoint =
        dc.getGlobe()
            .computePointFromPosition(
                namePosition.getLatitude(), namePosition.getLongitude(), elevation);
    Vec4 eyeVec = dc.getView().getEyePoint();

    double dist = eyeVec.distanceTo3(namePoint);
    return dist >= service.getMinDisplayDistance() && dist <= service.getMaxDisplayDistance();
  }
  private Vec4 computeReferencePoint(DrawContext dc) {
    if (dc.getViewportCenterPosition() != null)
      return dc.getGlobe().computePointFromPosition(dc.getViewportCenterPosition());

    java.awt.geom.Rectangle2D viewport = dc.getView().getViewport();
    int x = (int) viewport.getWidth() / 2;
    for (int y = (int) (0.5 * viewport.getHeight()); y >= 0; y--) {
      Position pos = dc.getView().computePositionFromScreenPoint(x, y);
      if (pos == null) continue;

      return dc.getGlobe().computePointFromPosition(pos.getLatitude(), pos.getLongitude(), 0d);
    }

    return null;
  }
    protected boolean isNavSectorVisible(
        DrawContext dc, double minDistanceSquared, double maxDistanceSquared) {
      if (!navSector.intersects(dc.getVisibleSector())) return false;

      View view = dc.getView();
      Position eyePos = view.getEyePosition();
      if (eyePos == null) return false;

      // check for eyePos over globe
      if (Double.isNaN(eyePos.getLatitude().getDegrees())
          || Double.isNaN(eyePos.getLongitude().getDegrees())) return false;

      Angle lat =
          clampAngle(eyePos.getLatitude(), navSector.getMinLatitude(), navSector.getMaxLatitude());
      Angle lon =
          clampAngle(
              eyePos.getLongitude(), navSector.getMinLongitude(), navSector.getMaxLongitude());
      Vec4 p = dc.getGlobe().computePointFromPosition(lat, lon, 0d);
      double distSquared = dc.getView().getEyePoint().distanceToSquared3(p);
      //noinspection RedundantIfStatement
      if (minDistanceSquared > distSquared || maxDistanceSquared < distSquared) return false;

      return true;
    }