Because the SATs only give you a pseudorange distance between you and the sat, so each say is most accurate solving for distance to/from that sat, and much less helpful resolving angle to the sat.
With a clear SkyView, around just under half of the sats are hidden by the earth.
This means that you get a full 360 degrees of data that can be near the horizon helping resolve lat/long.
But only about half of that sky is helpful for altitude. The birds you can't hear directly below the earth would be the most helpful for improving the altitude fix if you could hear them.
Baro is handy because you can take the absolute altitude from GPS as a low frequency baseline and use the baro for high frequency changes. Then when GPS says we teleported +200 feet when a new sat comes into view, we can temper that that with baro information.
Because the SATs only give you a pseudorange distance between you and the sat, so each say is most accurate solving for distance to/from that sat, and much less helpful resolving angle to the sat.
With a clear SkyView, around just under half of the sats are hidden by the earth.
This means that you get a full 360 degrees of data that can be near the horizon helping resolve lat/long.
But only about half of that sky is helpful for altitude. The birds you can't hear directly below the earth would be the most helpful for improving the altitude fix if you could hear them.
Baro is handy because you can take the absolute altitude from GPS as a low frequency baseline and use the baro for high frequency changes. Then when GPS says we teleported +200 feet when a new sat comes into view, we can temper that that with baro information.