Groundstation Playback - Altitude

[Gonch]

Hi,

Firstly id like to say what a brilliant tool the Groundstation Playback site is but was wondering if there were any ideas why on the Groundstation Playback site there is a large altitude difference compared to downloaded TRK file?

Eg on my flight yesterday the Groundstation playback showed -313ft when on the ground, compared to my TRK file height of 25ft with 10 satellites in view?

Thanks

[steveu]

Doesn't some maths have to be done to normalise all altitudes so traffic reporta are valid?

Mode S/ADS-B altitudes will be on 1013.2hPa so other ones will need to be made sync.

If pressure yesterday was about 1028 then this might explain a negative TO altitude?

Tracked a couple of aircraft yesterday and they also have -ve ground readings.

[Gonch]

Ahhh OK, I didn't think of the potential synching of Transponder altitudes, as mine was only putting out PAW according to the Playback.

Yesterday I had 1024/1025

Interesting clicking between the TRANSMISSION and seeing how much of it relied on CELLULAR only as no stations in sight.

[Admin]

Remember that adsb and mode-s use barometric altitude, flarm and PilotAware use gps
On the ground station there is an adjustment to convert gps to barometric, using the given local pressure setting

Thx
Lee

[tnowak]

Hi Lee,

Is that right that PAW and FLARM "radio" transmissions (not via ground station re-broadcast) send GPS altitudes and not barometric altitudes referenced to 1013.2 HPa?

Regards
Tony

[Admin]

That is correct, only a transponder emits barometric altitude, all other systems use gps
The groundstations emit altitude based upon the original emission type
Thx
Lee