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If you don't have other sensor data, like cell tower and Wifi, then GPS still has a pretty poor performance. Another problem of GPS is altitude. GPS is not real

If you don't have other sensor data, like cell tower and Wifi, then GPS still has a pretty poor performance. Another problem of GPS is altitude. GPS is not really designed to give a good altitude reading, especially when you are in the mountains where only get satellites readings from over your head and don't have readings from the satellites on the horizon. But in the mountains, altitude is also a very important information. I was up at basecamp in Nepal (south side) and Tibet (east and north side). The basecamp in Nepal is in a very tight spot. Bouncing signals is there a problem. Even radio is a problem. BTW: I commute daily with train, here in Germany. I play Pokemon and I have problems getting a GPS fix with the latest iPhone when I'm not directly at the window.

lxgr 3y ago
This used to be true many years ago, but today, even cheap phone receivers use a very high number of satellites (so geometry is usually more favorable) and usually also contain a barometer, which can provide additional disambiguation via sensor fusion. > especially when you are in the mountains where only get satellites readings from over your head That might be true in a very steep ravine, but it's more of a concern for reaching communications satellites (of which there are much fewer or sometimes only one, depending on the system). Today, not getting a GNSS fix due to terrain is increasingly unlikely for the reasons mentioned above. Also, in a hiking/mountaineering context, it's probably fair to assume that any GPS user will be located on the surface of the earth, so a precise lat/long fix is really all you need; you can determine the height using elevation models, which are pretty accurate these days. > I commute daily with train, here in Germany Some German trains were notorious for having bad cell signal due to metal-coated windows (applied for reflecting solar radiation). Try the same thing with an (open) car window and I bet you'll get excellent signal.
- mikestew 3y ago
  Some German trains were notorious for having bad cell signal due to metal-coated windows (applied for reflecting solar radiation). It's the first thing I thought of, and it's why we had ceramic tinting put on our vehicle windows instead of conventional tinting (which in many cases, AIUI, has radio-blocking metal in it).
mikestew 3y ago
But in the mountains, altitude is also a very important information. But wouldn't one carry a barometric altimeter in those cases? I mean, my iPhone and Apple Watch both have barometric altimeters, and those are consumer devices not designed to get you up a 7000m mountain. Now, granted, that doesn't help the device that's "sewn into a jacket", but as a sibling commenter mentions, in a search elevation models could be used. Or if they can stick an altimeter in my watch, maybe there's one in this mysterious, unnamed device. The basecamp in Nepal is in a very tight spot. Bouncing signals is there a problem. I wonder how much of a difference the newer dual-frequency GPS receivers make. It makes a difference on my Apple Watch Ultra versus an older Garmin when running around in the woods, but I'm no mountaineer.
- mthoms 3y ago
  Most anyone who climbs Everest knows their approximate altitude based on certain landmarks (waypoints) that are very well known. The most obvious of which are the camps (1 through 4) but there are other landmarks that are well known. If you're going off the main route however, then it's a bit of a different story.
mthoms 3y ago
Knowing your altitude on the main route is fairly easy. Those routes are entirely marked (roped) and have obvious geological features that mountaineers have memorized. The four camps en-route are also at the same altitude every year. Getting outside information about your altitude certainly is important if you're doing a non-standard route or if you stray from the fixed ropes somehow.

lxgr 3y ago

This used to be true many years ago, but today, even cheap phone receivers use a very high number of satellites (so geometry is usually more favorable) and usually also contain a barometer, which can provide additional disambiguation via sensor fusion. > especially when you are in the mountains where only get satellites readings from over your head That might be true in a very steep ravine, but it's more of a concern for reaching communications satellites (of which there are much fewer or sometimes only one, depending on the system). Today, not getting a GNSS fix due to terrain is increasingly unlikely for the reasons mentioned above. Also, in a hiking/mountaineering context, it's probably fair to assume that any GPS user will be located on the surface of the earth, so a precise lat/long fix is really all you need; you can determine the height using elevation models, which are pretty accurate these days. > I commute daily with train, here in Germany Some German trains were notorious for having bad cell signal due to metal-coated windows (applied for reflecting solar radiation). Try the same thing with an (open) car window and I bet you'll get excellent signal.

mikestew 3y ago
Some German trains were notorious for having bad cell signal due to metal-coated windows (applied for reflecting solar radiation). It's the first thing I thought of, and it's why we had ceramic tinting put on our vehicle windows instead of conventional tinting (which in many cases, AIUI, has radio-blocking metal in it).

mikestew 3y ago

But in the mountains, altitude is also a very important information. But wouldn't one carry a barometric altimeter in those cases? I mean, my iPhone and Apple Watch both have barometric altimeters, and those are consumer devices not designed to get you up a 7000m mountain. Now, granted, that doesn't help the device that's "sewn into a jacket", but as a sibling commenter mentions, in a search elevation models could be used. Or if they can stick an altimeter in my watch, maybe there's one in this mysterious, unnamed device. The basecamp in Nepal is in a very tight spot. Bouncing signals is there a problem. I wonder how much of a difference the newer dual-frequency GPS receivers make. It makes a difference on my Apple Watch Ultra versus an older Garmin when running around in the woods, but I'm no mountaineer.

mthoms 3y ago
Most anyone who climbs Everest knows their approximate altitude based on certain landmarks (waypoints) that are very well known. The most obvious of which are the camps (1 through 4) but there are other landmarks that are well known. If you're going off the main route however, then it's a bit of a different story.

mthoms 3y ago

Knowing your altitude on the main route is fairly easy. Those routes are entirely marked (roped) and have obvious geological features that mountaineers have memorized. The four camps en-route are also at the same altitude every year. Getting outside information about your altitude certainly is important if you're doing a non-standard route or if you stray from the fixed ropes somehow.