This is the driver for the original Sokkia Radian “real-time” GPS with centimeter accuracy.  Sokkia Radian GPS, like all real-time, high-accuracy GPS requires a base receiver sending corrections to a rover receiver.  Most commonly used GPS antenna types include the SK600 and SK502.  All Sokkia GPS receivers will accept and transmit RTCM, RTCA and CMR message strings.