uDig中增加Goolge 900913 坐标系的方法

uDig在图层属性里面设定属性如下：

PROJCS["Google_Mercator",
  GEOGCS["GCS_WGS_1984",
    DATUM["D_WGS_1984",
    SPHEROID["WGS_1984",6378137,0]
    ],
    PRIMEM["Greenwich",0],
    UNIT["Degree",0.017453292519943295]
  ],
  PROJECTION["Mercator"],
  PARAMETER["False_Easting",0],
  PARAMETER["False_Northing",0],
  PARAMETER["Central_Meridian",0],
  PARAMETER["Standard_Parallel_1",0],
  UNIT["Meter",1]
]