Oh sorry I did not think you were disagreeing I was just trying to be clear and more trying to clear up the GPS accuracy/reliability metrics like SIL, NIC, NACp and NACv being broadcast by ADS-B being completely separate to anything to do with pressure derived altitude, I was going down a rat hole and had to edit that several times. And it can be painfully confusing e.g. the failure flag for pressure altitude aka baro altitude in ADS-B speak failure is called NICbaro but has no relationship to the GPS NIC (Navigation Integrity Category) value. And depending on the system some of the GPS accuracy/reliability metrics are just hard coded, and the ones that really matter like NACp are derived from the GPS and SBAS reception.
John Wiseman does great stuff with ADS-B Out data.
Also for pilots/aircraft owners/A&Ps: The FAA PAPR (Public ADS-B Performance Report) https://adsbperformance.faa.gov/PAPRRequest.aspx provide a summary of their aircraft's ADS-B performance, including all the broadcast GPS quality metrics and any reported failure flags etc. The PAPR system will email out the PDF report. The owner/pilot/A&P can reply to that email and request a Google Earth/kmz and Spreadsheet/CSV data for that flight showing all the received ADS-B transmissions including all those accuracy/reliability metrics. Interesting stuff and very useful for diagnosing problems with ADS-B Out installations. So sensitive you'll might see say NACp degrade as an aircraft banks steeply because the GPS antenna now has a view of fewer GPS satellites. Installations in most (non-experimental/non-light sports) aircraft effectively require use of PAPR to formally validate a new installation is working correctly. It's a good thing for owners to also just periodically check their aircraft's ADS-B performance using PAPR. I suggest just before and after each annual inspection for GA/light aircraft.
John Wiseman does great stuff with ADS-B Out data.
Also for pilots/aircraft owners/A&Ps: The FAA PAPR (Public ADS-B Performance Report) https://adsbperformance.faa.gov/PAPRRequest.aspx provide a summary of their aircraft's ADS-B performance, including all the broadcast GPS quality metrics and any reported failure flags etc. The PAPR system will email out the PDF report. The owner/pilot/A&P can reply to that email and request a Google Earth/kmz and Spreadsheet/CSV data for that flight showing all the received ADS-B transmissions including all those accuracy/reliability metrics. Interesting stuff and very useful for diagnosing problems with ADS-B Out installations. So sensitive you'll might see say NACp degrade as an aircraft banks steeply because the GPS antenna now has a view of fewer GPS satellites. Installations in most (non-experimental/non-light sports) aircraft effectively require use of PAPR to formally validate a new installation is working correctly. It's a good thing for owners to also just periodically check their aircraft's ADS-B performance using PAPR. I suggest just before and after each annual inspection for GA/light aircraft.