I wonder how much this has changed in the intervening time period. My DJI Mini 3 Pro (from 2022) that I fly recreationally uses GPS and GLONASS to determine its location, and reports its altitude relative to its take-off location to single-meter precision. I haven't measured it, but it does seem reasonably accurate based on movements near the ground where I can estimate it. Though it also has downward-facing sensors which it uses for finding a more exact distance when it gets within a few meters of the ground, so it's not executing automated landings with GNSS alone.As far as GPS goes, yes, you can use it to derive your altitude, but it's really inaccurate. Too much so to use in flight. At my job, we use a system that is extremely precise. I've seen it triangulate our position with 12 GPS and 4 GLONASS satellites at once, and it's always accurate within a foot (usually centimeters) laterally. Even so, the GPS derived altitude is usually off by 100+ feet, sometimes as much as 300-400. That may sound pretty good, but when aircraft are being separated by only 500 feet, it's not nearly accurate enough. The FAA is really trying to pump out GPS WAAS instrument approaches, but they only provide lateral navigation. They can provide vertical navigation, but they use a trigonometry algorithm and the barometric altimeter to figure out what altitude you should be at.
Unfortunately, since it's only relative to your take-off point it's not as useful when flying where the terrain elevation changes rapidly, since it doesn't tell you your AGL height when you get higher than a few meters. Though it was amusing the one time I flew into an old open-pit mine in Arizona and was cruising around near the bottom with an altitude of "minus several hundred" meters.
Statistics: Posted by Philadelphus — 09 Apr 2025 19:48