@davecrawly Thank you for reviewing and summarizing the threads. I am against using GPSFix as base since it contains some data that is not well understood (like dip angle) but I may be mistaken. Thus, I would prefer NavSatFix as starting point adding the following:
- Velocity (in ENU frame) and attitude(*) (incl. covariances).
- Datum (datum in frame_id, antenna frame in child_frame_id).
- RTK status(**) and age
- GNSS time stamp (maybe incl. covariance wrt. position, ie., a 4x4 covariance matrix)
- Constellations (bitfield?)
(*) Attitude: dual antenna receivers: tilt angle might not correspond to roll or pitch. Antenna alignment wrt. base_link could be deduced from tf to child_frame_id.
(**) RTK: datum jumps possible + base stations do not transmit their datum, see here.