6 ms·

For those of us not deep into the technical details here: what's this mean?

by Forge36 4y ago

antegamisou 4y ago
Dual frequency mitigates the ionospheric delay error of GPS signals, yielding more accurate measurements.
- snovv_crash 4y ago
  This. Adding a second channel means that without RTK/PPK you can get ~30cm precision. The rest is just technical details.
  - lucb1e 4y ago
    For others who are not into that lingo, RTK/PPK are Real-Time and Post-Processed Kinematics. I had an idea of what the word kinematics means (Wikipedia says "describes the motion of [(groups of)] points") so this sounds like you use the accelerometer and gyroscope in addition to GNSS to get better accuracy, but actually no this has nothing to do with measuring your motion. Instead, RTK is something about signals' phase and requires an additional ground station (sounds similar to differential GPS, but by looking at phase data rather than position offset?), and PPK is never mentioned on Wikipedia and I don't understand descriptions from other sources. Post-processing is mentioned in differential GPS, however, to make the difference between the two topics (DGPS, RTK/PPK) even more confusing. If you could elaborate, I'd be interested. It seems very specialistic (though you drop it as if it should be obvious) so I doubt most people here know the terms.
    - snovv_crash 4y ago
      PPK uses exactly the same processing method as RTK, except rather than process in real-time it just logs the information and the merges with afterwards with the data logged from a base station. This is used primarily for remote sensing applications where centimeter accuracy of data is only needed in postprocessing and not at capture time - eg. drones with cameras for 3D reconstruction. The reason to use PPK is weight and cost - it just uses a normal GPS receiver and doesn't need an RTK sideband antenna, since the base station information can be downloaded over the internet at postprocessing time. RTK/PPK gives ~3cm precision, while standard GPS gives 6m precision. This new dual-band giving 30cm precision means it is good enough to not use RTK/PPK except in the most demanding applications.
yababa_y 4y ago
The short of it is that for the past two decade or so the us govt has been rolling out a new signal that the latest series of GPS satellites transmit that uses 1. more bandwidth, 2. more transmit power, 3. in a protected region of spectrum, 4. using modern encodings and error correction. This makes it a lot easier to pick up the signal from noisy environments.
- toomuchtodo 4y ago
  Are there any specific use cases where this will see outside benefit (urban areas)? Or is it just faster fix and higher precision without PPS/RTK?
  - tiernano 4y ago
    based on the keynote, they say it will be better in "urban jungles". It was part of the Apple Watch Ultra and said it worked better for the Boston (IIRC) Maraton. I would hope for the phone it works better for navagation in Car Play... I dont know how many times my phone things, when driving forward, that im turning down a side road...
    - hinkley 4y ago
      Return to the route. Return to the route. Return to the… FUCK YOU SHORESY, I’M ON THE ROUTE.
    - js2 4y ago
      Chicago Marathon. The Boston marathon is mostly a very open path. Source: I watched the keynote and I’ve run both.
    - willis936 4y ago
      That last bit is a software issue. Apple maps is constantly trying to route me to a parallel street for 1 block in a city and it actually thinks I listen to it. Google maps doesn't have either of these behaviors on the same hardware/APIs. No, a more accurate GPS will not fix Apple's bugs.
jtolmar 4y ago
GPS assumes* light travels in a straight line, which it doesn't due to atmospheric effects and reflections off buildings. L5 is a second frequency from the same satellites, which is affected by these problems differently, so the chip can compare the differences between the two signals and guess what's up with the atmosphere and buildings / throw out the dumber looking signal. It's also mostly independent so it's more data. L5 is also a bit less affected by atmosphere inherently. The upshot is much better accuracy in urban canyons, and a small improvement where GPS was already good. * Obviously people making chips and apps know this and try to mitigate it.
- chanandler_bong 4y ago
  Great, simple answer. Thank you!
- tomcam 4y ago
  That was infinitely better than TFA, thanks.
  - mikotodomo 4y ago
    the fucking article? edit: sorry
    - SpectralTheory 4y ago
      or, the fine article :)
- willis936 4y ago
  The single frequency situation isn't all that bad though since there are a dozen satellites in view and tracked even in urban outdoor environments.
  - s1mon 4y ago
    I live in San Francisco. We don't exactly have the tallest buildings, but I can assure you from years of tracking runs in the downtown area here and nearby forested areas, GPS gets very screwed up unless it has a clear view of the sky. This is with a variety of Garmins, Apple iPhones and Apple Watch. I'm looking forward to the newer devices with L5.

For those of us not deep into the technical details here: what's this mean?

antegamisou 4y ago

Dual frequency mitigates the ionospheric delay error of GPS signals, yielding more accurate measurements.

snovv_crash 4y ago
This. Adding a second channel means that without RTK/PPK you can get ~30cm precision. The rest is just technical details.
- lucb1e 4y ago
  For others who are not into that lingo, RTK/PPK are Real-Time and Post-Processed Kinematics. I had an idea of what the word kinematics means (Wikipedia says "describes the motion of [(groups of)] points") so this sounds like you use the accelerometer and gyroscope in addition to GNSS to get better accuracy, but actually no this has nothing to do with measuring your motion. Instead, RTK is something about signals' phase and requires an additional ground station (sounds similar to differential GPS, but by looking at phase data rather than position offset?), and PPK is never mentioned on Wikipedia and I don't understand descriptions from other sources. Post-processing is mentioned in differential GPS, however, to make the difference between the two topics (DGPS, RTK/PPK) even more confusing. If you could elaborate, I'd be interested. It seems very specialistic (though you drop it as if it should be obvious) so I doubt most people here know the terms.
  - snovv_crash 4y ago
    PPK uses exactly the same processing method as RTK, except rather than process in real-time it just logs the information and the merges with afterwards with the data logged from a base station. This is used primarily for remote sensing applications where centimeter accuracy of data is only needed in postprocessing and not at capture time - eg. drones with cameras for 3D reconstruction. The reason to use PPK is weight and cost - it just uses a normal GPS receiver and doesn't need an RTK sideband antenna, since the base station information can be downloaded over the internet at postprocessing time. RTK/PPK gives ~3cm precision, while standard GPS gives 6m precision. This new dual-band giving 30cm precision means it is good enough to not use RTK/PPK except in the most demanding applications.

yababa_y 4y ago

The short of it is that for the past two decade or so the us govt has been rolling out a new signal that the latest series of GPS satellites transmit that uses 1. more bandwidth, 2. more transmit power, 3. in a protected region of spectrum, 4. using modern encodings and error correction. This makes it a lot easier to pick up the signal from noisy environments.

toomuchtodo 4y ago
Are there any specific use cases where this will see outside benefit (urban areas)? Or is it just faster fix and higher precision without PPS/RTK?
- tiernano 4y ago
  based on the keynote, they say it will be better in "urban jungles". It was part of the Apple Watch Ultra and said it worked better for the Boston (IIRC) Maraton. I would hope for the phone it works better for navagation in Car Play... I dont know how many times my phone things, when driving forward, that im turning down a side road...
  - hinkley 4y ago
    Return to the route. Return to the route. Return to the… FUCK YOU SHORESY, I’M ON THE ROUTE.
  - js2 4y ago
    Chicago Marathon. The Boston marathon is mostly a very open path. Source: I watched the keynote and I’ve run both.
  - willis936 4y ago
    That last bit is a software issue. Apple maps is constantly trying to route me to a parallel street for 1 block in a city and it actually thinks I listen to it. Google maps doesn't have either of these behaviors on the same hardware/APIs. No, a more accurate GPS will not fix Apple's bugs.

jtolmar 4y ago

GPS assumes* light travels in a straight line, which it doesn't due to atmospheric effects and reflections off buildings. L5 is a second frequency from the same satellites, which is affected by these problems differently, so the chip can compare the differences between the two signals and guess what's up with the atmosphere and buildings / throw out the dumber looking signal. It's also mostly independent so it's more data. L5 is also a bit less affected by atmosphere inherently. The upshot is much better accuracy in urban canyons, and a small improvement where GPS was already good. * Obviously people making chips and apps know this and try to mitigate it.

chanandler_bong 4y ago
Great, simple answer. Thank you!
tomcam 4y ago
That was infinitely better than TFA, thanks.
- mikotodomo 4y ago
  the fucking article? edit: sorry
  - SpectralTheory 4y ago
    or, the fine article :)
willis936 4y ago
The single frequency situation isn't all that bad though since there are a dozen satellites in view and tracked even in urban outdoor environments.
- s1mon 4y ago
  I live in San Francisco. We don't exactly have the tallest buildings, but I can assure you from years of tracking runs in the downtown area here and nearby forested areas, GPS gets very screwed up unless it has a clear view of the sky. This is with a variety of Garmins, Apple iPhones and Apple Watch. I'm looking forward to the newer devices with L5.