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> Climbers have successfully used GPS devices for many years, but they are not 100% reliable. [...] Sometimes, it will send incorrect coordinates because the si

> Climbers have successfully used GPS devices for many years, but they are not 100% reliable. [...] Sometimes, it will send incorrect coordinates because the signal bounces off the mountain walls. Also, they require a clear sky view Somewhat, but GPS receiver performance has improved greatly in the last 25 years. Back in the day, you'd put a carefully oriented GPS antenna on the top of your car and still expect to lose signal when going between tall buildings. These days a backseat car passenger with a metal car roof between them and the sky, paying no attention to the antenna's orientation, can almost always get a fix even in the densest of built up areas. And it's not just wifi or cell tower tracking - it's a proper satellite fix, with the precision to give turn-by-turn navigation instructions in good time. A mountaineer's personal locator beacon might not get the full benefits (unlike a smartphone in an urban area, they probably won't get the fast fix A-GPS provides) but I'd still expect them to get the high sensitivity and multipath rejection modern receivers provide.

asdaq1312512 3y ago
I thought the same, but I was pretty surprised how bad my phone's GPS performance was next to cliffs. Especially altitude was off significantly. When thinking of turn-by-turn navigation, keep in mind that car navigation will snap your position to roads. For a better comparison, try e.g. Google Maps in pedestrian or bicycle navigation mode. At least in my experience, the perceived "accuracy" drops significantly.
- londons_explore 3y ago
  If you have a USA phone, bear in mind most are sold with glonass and beidou and support disabled. Buy a phone or GPS from elsewhere in the world and you'll get to use all the networks and get much better accuracy.
  - asdaq1312512 3y ago
    EU phone, but yeah, good to point out GNSS isn't just GPS anymore. I also agree that the accuracy is insanely good most of the time; I'm just objecting the "accuracy test" using car turn-by-turn navigation :-)
  - ryandrake 3y ago
    Do you have a source on that? My understanding is that most consumer cellphone GNSS systems today are multi-constellation out of the box. If there is a satellite up there, the phone will use it, no matter which flag is painted on it.
- blutack 3y ago
  Additionally, phone GPS chipsets are often built into the baseband modem and performance might be limited compared to state of the art (and just price, packaging limitations for antennas, assumption that a phone always uses A-GPS etc). The dual frequency chipsets used in modern high-end fitness watches & drones have pretty spectacular performance even in incredibly built up areas with high tower blocks or under tree cover (they usually have a barometer as well to help with the altitude problem).
- michaelt 3y ago
  > keep in mind that car navigation will snap your position to roads. Right. I chose driving as an example because someone navigating a city on foot could conceivably do it with low-precision signals like wifi. They can stop and wait for a better signal, or carefully study the map comparing it to street signs; a fix that puts them on the right block and that only updates once or twice per block is adequate, if not good. Whereas turn-by-turn navigation is able to tell the driver "take the next right" 3 seconds before the turn - which shows the signal is being tracked precisely and regularly. > For a better comparison, try e.g. Google Maps in pedestrian or bicycle navigation mode. If you're into sports, take a look on Strava at people doing things like big city marathons: https://www.strava.com/activities/8078299417 https://www.strava.com/activities/8078299417 https://www.strava.com/activities/51910242 https://www.strava.com/activities/51910242 where of course the positions aren't snapped to roads. You'll see minor hiccups from time to time - but despite navigating between many tall buildings, you won't see errors of hundreds of miles.
  - icegreentea2 3y ago
    GPS units can also include INS or INS like logic systems to prevent those types of jumping around. It can be difficult to tell from an application output just how processed your "dot" is.
    - michaelt 3y ago
      It's actually fairly easy, for things like running GPSes. You know the track isn't snapped to a map. And you know it's not built into a car, so no odometer or rate gyro. Then just look at the trace as the sportsperson goes around a corner. Does the trace overshoot, then backtrack? That means the kalman filter is heavily smoothing with momentum. Does it produce a gently rounded corner that goes through a building? That means there's a moving average. However if the traces display sharp corners when appropriate - then the signal is not being excessively smoothed. (And I can assure you, even if a GPS watch has enough motion sensing to count steps, the swinging of arms and bouncing of feet mean wrist acceleration is noisy enough you've got no chance of detecting a runner turning a corner)
etrautmann 3y ago
Your phone is using other signals, like maps of WiFi ssids to help locate in gps denied areas.
jsjohnst 3y ago
> it's a proper satellite fix, with the precision to give turn-by-turn navigation instructions in good time That’s not entirely true. Phones do sensor fusion when doing turn by turn navigation. Accelerometer, gyro, and barometer are especially taken into account, but also compass and trilateration via WiFi and cellular sources as well.
- spacecadet 3y ago
  Dropped in just to say, no one understands GPS, including 99% of hacks and tech people... Go buy a $5 dongle and stream the feed, its just lat/long repeating maybe sometimes a altitude... but its still very weak and very unreliable... with mobile phones pulling wool to make you all believe its turn by turn. Ok bye.
  - jsjohnst 3y ago
    > Dropped in just to say, no one understands GPS, including 99% of hacks and tech people... Go buy a $5 dongle and stream the feed, its just lat/long repeating maybe sometimes a altitude... So you’re also one of the 99%! That “feed” isn’t the GPS signal, it’s the output of your cheap device. ;) There are folks here however who are intimately familiar with gold codes, legendre sequences, Jaffe-Rechtin phase locked loops, RHCP signals, URA vs URE, etc.
    - spacecadet 3y ago
      Thanks Karen! Was suggesting people learn these concepts through the use of a usb dongle, but turns out you're the dongle.
- lxgr 3y ago
  Google does something pretty clever specifically for urban canyons too: https://blog.research.google/2019/02/using-global-localization-to-improve.html https://blog.research.google/2019/02/using-global-localizati... In my (limited, I don't often use my Pixel) experience, it does work much better than my iPhone's GPS, which often wants me to use the camera (in Apple and Google Maps) for urban canyon navigation using visual sensor fusion.
PinguTS 3y ago
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).

asdaq1312512 3y ago

I thought the same, but I was pretty surprised how bad my phone's GPS performance was next to cliffs. Especially altitude was off significantly. When thinking of turn-by-turn navigation, keep in mind that car navigation will snap your position to roads. For a better comparison, try e.g. Google Maps in pedestrian or bicycle navigation mode. At least in my experience, the perceived "accuracy" drops significantly.

londons_explore 3y ago
If you have a USA phone, bear in mind most are sold with glonass and beidou and support disabled. Buy a phone or GPS from elsewhere in the world and you'll get to use all the networks and get much better accuracy.
- asdaq1312512 3y ago
  EU phone, but yeah, good to point out GNSS isn't just GPS anymore. I also agree that the accuracy is insanely good most of the time; I'm just objecting the "accuracy test" using car turn-by-turn navigation :-)
- ryandrake 3y ago
  Do you have a source on that? My understanding is that most consumer cellphone GNSS systems today are multi-constellation out of the box. If there is a satellite up there, the phone will use it, no matter which flag is painted on it.
blutack 3y ago
Additionally, phone GPS chipsets are often built into the baseband modem and performance might be limited compared to state of the art (and just price, packaging limitations for antennas, assumption that a phone always uses A-GPS etc). The dual frequency chipsets used in modern high-end fitness watches & drones have pretty spectacular performance even in incredibly built up areas with high tower blocks or under tree cover (they usually have a barometer as well to help with the altitude problem).
michaelt 3y ago
> keep in mind that car navigation will snap your position to roads. Right. I chose driving as an example because someone navigating a city on foot could conceivably do it with low-precision signals like wifi. They can stop and wait for a better signal, or carefully study the map comparing it to street signs; a fix that puts them on the right block and that only updates once or twice per block is adequate, if not good. Whereas turn-by-turn navigation is able to tell the driver "take the next right" 3 seconds before the turn - which shows the signal is being tracked precisely and regularly. > For a better comparison, try e.g. Google Maps in pedestrian or bicycle navigation mode. If you're into sports, take a look on Strava at people doing things like big city marathons: https://www.strava.com/activities/8078299417 https://www.strava.com/activities/8078299417 https://www.strava.com/activities/51910242 https://www.strava.com/activities/51910242 where of course the positions aren't snapped to roads. You'll see minor hiccups from time to time - but despite navigating between many tall buildings, you won't see errors of hundreds of miles.
- icegreentea2 3y ago
  GPS units can also include INS or INS like logic systems to prevent those types of jumping around. It can be difficult to tell from an application output just how processed your "dot" is.
  - michaelt 3y ago
    It's actually fairly easy, for things like running GPSes. You know the track isn't snapped to a map. And you know it's not built into a car, so no odometer or rate gyro. Then just look at the trace as the sportsperson goes around a corner. Does the trace overshoot, then backtrack? That means the kalman filter is heavily smoothing with momentum. Does it produce a gently rounded corner that goes through a building? That means there's a moving average. However if the traces display sharp corners when appropriate - then the signal is not being excessively smoothed. (And I can assure you, even if a GPS watch has enough motion sensing to count steps, the swinging of arms and bouncing of feet mean wrist acceleration is noisy enough you've got no chance of detecting a runner turning a corner)

etrautmann 3y ago

Your phone is using other signals, like maps of WiFi ssids to help locate in gps denied areas.

jsjohnst 3y ago

> it's a proper satellite fix, with the precision to give turn-by-turn navigation instructions in good time That’s not entirely true. Phones do sensor fusion when doing turn by turn navigation. Accelerometer, gyro, and barometer are especially taken into account, but also compass and trilateration via WiFi and cellular sources as well.

spacecadet 3y ago
Dropped in just to say, no one understands GPS, including 99% of hacks and tech people... Go buy a $5 dongle and stream the feed, its just lat/long repeating maybe sometimes a altitude... but its still very weak and very unreliable... with mobile phones pulling wool to make you all believe its turn by turn. Ok bye.
- jsjohnst 3y ago
  > Dropped in just to say, no one understands GPS, including 99% of hacks and tech people... Go buy a $5 dongle and stream the feed, its just lat/long repeating maybe sometimes a altitude... So you’re also one of the 99%! That “feed” isn’t the GPS signal, it’s the output of your cheap device. ;) There are folks here however who are intimately familiar with gold codes, legendre sequences, Jaffe-Rechtin phase locked loops, RHCP signals, URA vs URE, etc.
  - spacecadet 3y ago
    Thanks Karen! Was suggesting people learn these concepts through the use of a usb dongle, but turns out you're the dongle.
lxgr 3y ago
Google does something pretty clever specifically for urban canyons too: https://blog.research.google/2019/02/using-global-localization-to-improve.html https://blog.research.google/2019/02/using-global-localizati... In my (limited, I don't often use my Pixel) experience, it does work much better than my iPhone's GPS, which often wants me to use the camera (in Apple and Google Maps) for urban canyon navigation using visual sensor fusion.

PinguTS 3y ago

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).