To get the heading line you need some compass
data into OCPN like the NMEA0183 sentences HDT, HDM etc. The GPS
course gives a course over ground, COG, and that's not all time the same as the ship's heading and consequently not used for the heading line.
Rate of turn, ROT
First is this data mostly calculated by a gyro or a satellite
Seconds is, what I'm aware of, the ROT data for own ship not used by OCPN anywhere. It's though reported by the AIS
type A target's detailed information. (AIS type B does not report ROT)