/**
   * {@inheritDoc}
   *
   * @param positions Control points. This graphic uses only two control point, which determine the
   *     midpoints of two opposite sides of the quad. See Fire Support Area (2.X.4.3.2.1.2) on pg.
   *     652 of MIL-STD-2525C for an example of how these points are interpreted.
   */
  public void setPositions(Iterable<? extends Position> positions) {
    if (positions == null) {
      String message = Logging.getMessage("nullValue.PositionsListIsNull");
      Logging.logger().severe(message);
      throw new IllegalArgumentException(message);
    }

    Iterator<? extends Position> iterator = positions.iterator();
    try {
      Position pos1 = iterator.next();
      Position pos2 = iterator.next();

      LatLon center = LatLon.interpolateGreatCircle(0.5, pos1, pos2);
      this.quad.setCenter(center);

      Angle heading = LatLon.greatCircleAzimuth(pos2, pos1);
      this.quad.setHeading(heading.subtract(Angle.POS90));

      this.positions = positions;
      this.shapeInvalid = true; // Need to recompute quad size
    } catch (NoSuchElementException e) {
      String message = Logging.getMessage("generic.InsufficientPositions");
      Logging.logger().severe(message);
      throw new IllegalArgumentException(message);
    }
  }