Does a 1 or 2 meter difference in the combined antenna and ground elevation figure impact MLAT synchronization?
The reason I ask is that when I change that, both plus and minus, the sync numbers seem to go down.
I did wait a few hours after the changes, so it’s not a case of seeing a drop immediately after they were made. And I also compared between 2 receivers. The one with the ‘optimum’ number had more sync sites, consistently.
They both have the same ‘optimum’ number now, and they both show the same number of sync sites at the higher end.
Thank you for asking this question - I was considering asking the same thing. My own antenna is approximately 4 storeys up (not exactly sure of the precise elevation vs. ground so I have entered an estimate for the time being) and I have noticed that my MLAT sync is sometimes orange when I check my PiAware instance.
I’m going to have to try a few apps - the ones I looked at were either not reporting actual altitude or were not sufficiently accurate (i.e., reported higher altitude at ground level than at antenna height).
To my point about accuracy, check out this table showing how innacurate a variety of consumer devices can be:
On the iPhone the built in compass app will give you your elevation. Make sure it has access to location services:
Settings / Privacy / Location Services / Compass → make sure set to “While Using the App”.
Launch the Compass app. At the bottom it gives you your Lat / Lon and your elevation in metres above mean sea level. It can take a few seconds to settle.
On the iPhone … Launch the Compass app … it gives you your Lat / Lon and your elevation in metres above mean sea level. It can take a few seconds to settle.
I’m not sure how the iOS Compass app attempts to do this but I have replicated the faulty or at least unhelpfully inaccurate data I saw previously. This time at ground level I get 160m and on the 4th floor of my building I get 150m (i.e., 10m less, despite the elevator ride up). There was no apparent “settling” involved, just an instant and unchanging reading in both cases.
The iPhone 6, 6S, 7, 8 and X have a barometric pressure sensor which is used to help determine elevation and changes in elevation, and location services makes use of a combination of GPS, cell towers, crowd-sourced WiFi hotspots and bluetooth to determine location. It’s not strictly necessary to have a clear view of the sky and a four satellites visible to get usable location and elevation data with these models. It’s iOS’s location services which obtains all this data, and all apps simply hook into location services so are all be equally capable of displaying usable data.
