The CAT I is a stand-alone high accuracy GPS receiver with the capability of GPS/GLONASS and available SBAS systems such as EGNOS, WAAS, MSAS, and GAGAN  

CAT I is an add-on option to CAT ROT for use in operations that demand more accurate positioning than what is provided by the ship’s own positioning through the AIS pilot plug. The use of CAT I further improves the accuracy of the speed measurements of own vessel.

The CAT ROT / CAT I solution is thus independent of the ship’s positioning and speed sources. The only data still provided by the vessel’s pilot plug is heading data and AIS targets, which is less sensitive data as the pilot can easily validate the quality.