This assigns x,y,z earth-fixed Geocentric coordinates. In order to render other spatial reference frames they will normally be converted into this form.
(<x>, <y>, <z>). These values are all given in units of metres. The coordinate represents an offset from the center of the planet, based upon the WGS84 ellipsoid. The z-axis passes through the poles while the x-axis cuts through the latitude/longitude coordinate (0,0) degrees. For example,
(-2700301, -4290762, 3857213) is the geocentric coordinate for Menlo Park, California, USA.
No additional arguments are supported. An example spatial reference frame definition of this format is [ "GC" ].