Explaination of Altitude

[kevinrobson17]

Not really a feature request, but I wondered in the absence of a full user guide the devs could explain exactly how altitude works on this device?

From what I can see we have: Alt 1 - adjustable using the baraometer Alt 2 - adjustable using the barometer Altitude graph - which does this actually show - which of these metrics? Take-off - not sure what this is but is in feet. Is this height above takeoff zone? If so, how is that worked out? does it get zeroed when we take off and start gaining height? Altitude GNSS - no idea what this is (GPS altitude maybe?) Height above GROUND - using the mapping files, but what does it map to - presumably it needs to reference either alt1 or alt2? Height above TO - what deoes this represent if no waypoint set

So 1 and 2 are adjustable. What should they be set to? QNH? QFE? Does it matter? Is anything else based off this reading?

Which of the above altitudes is recorded in the flight logs? Which of the above altitudes is used for FLARM? What should our preflight configuration be i.e. what should we set when we first switch the device on for everything to give accurate info.

I've only done a few flights, but I've definitely come across a few anomalies where I've been flying at minus 300 ft. I'm sure that's just a case of setting the wrong altimeter to the wrong value, but it would be good to full understand what these all are and how they interact with each other.

Thanks

[fhorinek]

Alt 1 - adjustable using the baraometer

Set it to correct QNH, on by selecting a widget and setting correct altitude , this is your altitude for vario

Alt 2 - adjustable using the barometer

Only if you need altitude based on fixed pressure, usable with flight levels or other restrictions, only for your info

Altitude graph - which does this actually show - which of these metrics?

Altitude1

Take-off - not sure what this is but is in feet. Is this height above takeoff zone? If so, how is that worked out? does it get zeroed Height above TO - what deoes this represent if no waypoint set

Same widget, it is zeroed when takeoff is detected and then shows differential to your Alt1 (positive above, negative below) Units are selectable in settings

Altitude GNSS - no idea what this is (GPS altitude maybe?)

GNSS is term to describe multiple positions systems, strato is using GPS, GLONAS and Galileo for simplicity GPS == GNSS

Height above GROUND

from agl files, relative to GNSS alt

According to specification: IGC is using barometric altitude normalized to 101325 Pa + GNSS (GPS) altitude above ellipsoid FLARM is using GNSS (GPS) altitude above msl

At takeoff, select Alt1 widget and set it to the takeoff known height. Automatic altitude calibration from GNSS will be implemented soon.

[kevinrobson17]

Thank you for the explaination. That all makes a lot more sense. So altitude 1 effectively becomes height above sea level.

I guess the only question I have now, is why do we use GNSS altitude (which as I understand it isn't very accurate) for FLARM and for Height above ground level when we presumably have a more accurate ALT1. Although I suppose this does depend on whether the user has set it correctly.

Or perhaps ALT1 can be set automatically using a combination of ALT1 at takeoff and the AGL files, and maybe GNSS to cross check assumptions? It just seems a little strange to be using solely GPS altitude for some functions, even though from my experience it isn't usually that accurate.

I may have missed it, but which altitude gets written to the logs?

I'll try it that way when I next fly. I was zeroing ALT1 on the ground, so that will almost certainly have caused some of the strange readings I found.

Thanks again for the explaination, and for all of the developers work on this device.

[Skyhighpara]

According to specification: IGC is using barometric altitude normalized to 101325 Pa + GNSS (GPS) altitude above ellipsoid

IGC = tracklog file.