Regarding the following PGNs that NovAtel receivers output:
PGN 129029 GNSSPositionData,
PGN 129025 GNSSPositionRapidUpdate,
PGN 129026 COGandSOGRapidUpdate.
The message formats for the CAN PGNs are part of NMEA 2000 Standard. NMEA does not give this information for free. You need to purchase decoding information NMEA 2000® Appendix B NAVIGATION SUBSET PGN from NMEA: http://www.nmea.org/store/index.asp?show=cprd&cid=7
Although NovAtel strives to openly provide as much information as possible from our receivers, we are bound by NMEA 2000s copyright on this standard.
You can contact NMEA for more information http://www.nmea.org/content/contactus/contactus.asp