@Joel Sanchez that 8-12m disagreement is completely expected and you're not misconfiguring anything — those two altitude sources are measuring fundamentally different things. The GNSS module is giving you ellipsoidal height (distance from the WGS84 mathematical ellipsoid), while barometric altitude is referenced to a standard atmosphere pressure model, and the two can diverge by anywhere from a few meters to 50+ meters depending on location and weather, so that delta you're seeing is actually pretty normal.
For a UAV logging build, the practical answer is: use barometric pressure for relative altitude (height above your launch point) and GNSS for absolute positioning. Baro is much more responsive to short-term altitude changes and doesn't have the vertical dilution of precision issues GNSS suffers from, but it drifts with temperature and weather over time. GNSS vertical accuracy is inherently weaker than horizontal — you're typically looking at 2-3x worse on the Z axis.
The real-world best practice here is sensor fusion — weight baro heavily for rate-of-climb and short-term altitude hold, and use GNSS to correct for baro drift over longer periods. If you're just logging and not doing active altitude control, I'd record both channels and apply a complementary filter in post. That way you've got the responsiveness of baro and the absolute reference from GNSS without committing to one source.
