code: function(rectangle, position, direction, up) {
    if (!defined(rectangle)) {
      throw new DeveloperError("rectangle is required.");
    }
    if (defined(position) || defined(direction) || defined(up)) {
      if (!defined(position) || !defined(direction) || !defined(up)) {
        throw new DeveloperError(
          "If any of position, direction, or up are specified, all must be specified."
        );
      }
    }
  
    this._rectangle = rectangle;
    this._position = position;
    this._direction = direction;
    this._up = up;
  }
docs: Holds a camera view parameters, expressed as a rectangular extent and/or as a camera position, direction,
  and up vector.
  
  @alias CameraView
  @constructor