You would need to get a facing direction. Most robots are doing that with a magnetometer, gyros and an extended Kalman filter. This has quite a few disadvantages though. First and foremost the magnetometer which is really your source of truth is unreliable. It wanders constantly and frequently your Kalman filter will start up in a bad state.
With 3 or 4 channels you could use the GPS almanac to get satellite direction and your heading. Though you could do it with two if you could get two antennas a couple of feet apart. But smaller robots don't have that kind of room.
Right now I think the biggest pain point with GPS is that if I want single redundancy GPS with 2 CM precision and true heading I need a whole bunch of stuff. 2x 200$ GPS receivers (ublox f9p) on my robot. 1x 200$ receiver with a decent antenna and a xbee radio to act as a RTK base station. And this was just for a simple outdoor rover. And the base station always had to go in the same place because you have to do everything relative to the base station. Then you need all the software to coordinate all that and manage everything.
I want 1 receiver unit, global absolute position within 2 CM with a true heading. Additionally, I want seamless transitioning/augmentation with a global network of terrestrial beacons for interiors and areas with poor surface coverage. And I want all that in a 100$ish module and some sort of subscription.
Have you looked into using gyros for north-finding? There's been a lot of progress in recent years with MEMS gyros (which normally have too much zero-drift to work with traditional gyro north-finding techniques).
That's a pretty neat technique. It seems superficially similar to how mems magnetometers work. The size and oscillation make me question how robust that is though.
One stop gap solution I has was just an IR beacon on my GPS base station. I got an initial alignment with the rover camera and my two gps points. But ended up adding a second gps to the rover.
I've seen some multi channel GPS front ends like this one: https://www.crowdsupply.com/amungo-navigation/nut2nt-plus
With 3 or 4 channels you could use the GPS almanac to get satellite direction and your heading. Though you could do it with two if you could get two antennas a couple of feet apart. But smaller robots don't have that kind of room.
Right now I think the biggest pain point with GPS is that if I want single redundancy GPS with 2 CM precision and true heading I need a whole bunch of stuff. 2x 200$ GPS receivers (ublox f9p) on my robot. 1x 200$ receiver with a decent antenna and a xbee radio to act as a RTK base station. And this was just for a simple outdoor rover. And the base station always had to go in the same place because you have to do everything relative to the base station. Then you need all the software to coordinate all that and manage everything.
I want 1 receiver unit, global absolute position within 2 CM with a true heading. Additionally, I want seamless transitioning/augmentation with a global network of terrestrial beacons for interiors and areas with poor surface coverage. And I want all that in a 100$ish module and some sort of subscription.