Altitude Above Ground (AGL)

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Three altitudes, one display

Pilots think in three altitudes — and travelers should too:

• MSL (Mean Sea Level) — the number you usually want. “We’re flying at 11 km.”
• AGL (Above Ground Level) — your height above the terrain directly below. Over the Alps your AGL is far less than your MSL.
• WGS84 ellipsoidal — the raw GPS altitude before geoid correction. Mostly relevant for engineers, but Skyty exposes it.

Tap once in settings to switch between them. The instrument panel updates instantly.

How AGL is computed offline

To know AGL, you need to know the elevation of the ground beneath you. Skyty downloads NASA SRTM terrain data — the same dataset used in aviation cockpits — once, on WiFi at home (~900 MB). After that, every GPS fix is enriched with a terrain elevation lookup, so AGL is computed locally without ever calling a server.

Vertical speed too

While we’re at it, Skyty smooths the altitude time series and reports your vertical speed in m/s — useful during climb-out and descent. You’ll see the rate spike to ~10 m/s on take-off and settle into ±0.5 m/s once you reach cruise.

Why it matters

Knowing you’re 11 km above sea level is one thing. Knowing you’re 8.5 km above a glacier is another. AGL is what tells you whether you’re really up there, or whether you’re skimming over high terrain. It’s also what makes mountain views from window seats so breathtaking — when the AGL number drops, look out the window.