public static function Eform(iauRefEllips $n, &$a, &$f) {
    /* Look up a and f for the specified reference ellipsoid. */
    switch ($n->value) {

      case WGS84:
        $a = 6378137.0;
        $f = 1.0 / 298.257223563;
        break;

      case GRS80:
        $a = 6378137.0;
        $f = 1.0 / 298.257222101;
        break;

      case WGS72:
        $a = 6378135.0;
        $f = 1.0 / 298.26;
        break;

      default:

        /* Invalid identifier. */
        $a = 0.0;
        $f = 0.0;
        return -1;
    }

    /* OK status. */
    return 0;
  }