3 ms·
GPS provided elevation data is bad, like really really bad. Often tens of meters out of sync. Unlikely this would work well in practice without additional locat
by m4rtink 7y ago
GPS provided elevation data is bad, like really really bad. Often tens of meters out of sync. Unlikely this would work well in practice without additional location data sources (barometer, camera based tracking, etc.).
- SketchySeaBeast 7y agoI was intrigued by this, so here's a quick explanation by Garmin: https://support.garmin.com/en-CA/?faq=QPc5x3ZFUv1QyoxITW2vZ6 https://support.garmin.com/en-CA/?faq=QPc5x3ZFUv1QyoxITW2vZ6 Important quote: "It is not uncommon for satellite heights to be off from map elevations by +/- 400 ft." Wow.
- eigenvector 7y agoYes, this is why most backcountry navigation apps don't display GPS elevation to the user, instead they use the lat/long to look up the position on a topographical map and report that elevation instead. In very steep terrain, it's always a good idea to employ a conventional (barometric) altimeter.
- SketchySeaBeast 7y agoGenuinely curious - what would you need moment by moment readings for? My experience with back country camping is the Rockies, so I've never been at any sort of altitude danger zone, and it's usually pretty binary - you're either on top of the mountain or still not. For something like a GPS watch I'd just want to look back on it later to be able to review my route, but I can't see myself taking barometric measurements for accuracy.
- sushisource 7y agoInternet points, really. A more accurate elevation read gives you a more accurate ability to boast about how brutal your hike was :)
- eigenvector 7y agoIn steep terrain, elevation is a great way to find your location. Suppose I know that I'm on a certain lateral feature - a ridge, canyon, or watercourse. By knowing my precise elevation, I can determine my exact location. This helps me navigate as well as quickly guesstimate my current pace / progress. If I know I will spend all day ascending gradually on a valley glacier from 4000 m to 5000 m, in 1 second I can check my altimeter and know how far I've come when a handheld GPS will spend 30 seconds trying to get a fix. If someone is trying to state the location of, for instance, a good bivy site on a rock climbing route, "1890 m on the SE ridge" is equally as precise as the GPS coordinates, but much more descriptive.
- SketchySeaBeast 7y agoAh, I didn't think of rock climbing.
- userbinator 7y agoThe negative part is also very true --- I've had a GPS tell me I was deep underground, when in fact I was on top of a hill.
- walrus01 7y agoGPS elevation data on a modern device with a sufficiently good view of the sky is often, but by no means guaranteed, to be a lot better than that. On a really cheap smartphone with GPS+GLONASS receive ability you can regularly see 12 to 14 satellites. The more satellites, the better the Z axis precision. Anecdotally, when standing next to FCC licensed radio systems on roofs, which are supposed to have accurate license data in their database entries for height MSL and AGL, I have seen elevation data from my late-2019 vintage smartphone just as accurate as on a $5000 surveying GPS. At least to within 2-3 meter Z axis of reality.