WITSML - Well Coordinate Reference System Component Schema. Note that this is intended for use with two dimensional coordinates. That does not prevent the use of a three dimensional CRS. It just means that only two coordinates will be specified in that 3D system. The veritcal coordinates are specified separately and, for 3D systems, one of the linked wellDatums should represent the vertical datum of that 3D system so that the height in the 3d system can be determined. Human recognizable context for the system. For a geographic system this is commonly the name of the datum. Each well CRS can only represent only one type of system. Note that these structures do not truly define a CRS but rather specify information that could be used to describe a CRS. Map projection system. Geographic system. Local (engineering) system. A textual description of the system. The unique identifier of the system.