EPSG:2451

平面直角座標系 IX 系の EPSG コード。
GeoTools の出力によると、この座標系の定義は以下の通り:

PROJCS["JGD2000 / Japan Plane Rectangular CS IX", 
  GEOGCS["JGD2000", 
    DATUM["Japanese_Geodetic_Datum_2000", 
      SPHEROID["GRS 1980", 6378137.0, 298.257222101, AUTHORITY["EPSG","7019"]], 
      TOWGS84[0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0], 
      AUTHORITY["EPSG","6612"]], 
    PRIMEM["Greenwich", 0.0, AUTHORITY["EPSG","8901"]], 
    UNIT["degree", 0.017453292519943295], 
    AXIS["Longitude", EAST], 
    AXIS["Latitude", NORTH], 
    AUTHORITY["EPSG","4612"]], 
  PROJECTION["Transverse_Mercator"], 
  PARAMETER["central_meridian", 139.83333333333334], 
  PARAMETER["latitude_of_origin", 36.0], 
  PARAMETER["scale_factor", 0.9999], 
  PARAMETER["false_easting", 0.0], 
  PARAMETER["false_northing", 0.0], 
  UNIT["m", 1.0], 
  AXIS["x", EAST], 
  AXIS["y", NORTH], 
  AUTHORITY["EPSG","2451"]]