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With an up to date AGPS database, GPS is quite usable. AGPS is also distributed as a service, though, often by companies that made the GPS receiver chips. If th

With an up to date AGPS database, GPS is quite usable. AGPS is also distributed as a service, though, often by companies that made the GPS receiver chips. If that were to fall away, you'd struggle to make GPS usable for phones. You may not need Google for a GPS lock, but you certainly can't get a good fix without an external party. I've unwittingly tried this, when I saw a weird HTTP URL on my network being polled in the background; I blocked it in my Pihole and found out not much later that my phone's GPS started taking longer and longer to get a fix. Not "waving your phone 30 minutes at a clear sky" long, but definitely to the point where using Google Maps with cell/WiFi scanning disabled become very annoying.

dgacmu 3y ago
I run a modest fleet of mostly-offline data collection devices that rely on GPS; we pay a lot of attention to how long it takes before they can sync. With a good sky view, the GPS chip often has a 3D position lock before Linux has finished booting. What you're seeing is the effect of AGPS and the interaction with the phone's aggressive power management. https://en.m.wikipedia.org/wiki/Assisted_GNSS https://en.m.wikipedia.org/wiki/Assisted_GNSS It's not really a limitation of GPS, it's about using the external service to let you minimize the time your GPS receiver is active. You can get a great fix without AGPS, but you can't both keep the GPS off 99.9% of the time _and_ get a fast, great position fix.
- jeroenhd 3y ago
  Fair enough, I suppose. I think in the context of smartphones, continuously operating the GPS chip is simply not an option, but in other types of devices that isn't as big of a problem.
- seba_dos1 3y ago
  > You can get a great fix without AGPS Yes, after waiting minutes with good line of sight for almanac and ephemerides to download from the satellites. Anything that gets a fix faster is already "assisted", usually either by fresh data downloaded online or not-yet-fully-out-of-date data stored locally.
  - dgacmu 3y ago
    Sure. I was simply observing that this phrasing: > but you certainly can't get a good fix without an external party. is not true. You can get a great fix without a third party. You just have to be more patient for your TTFF. * Unless you want RTK-level accuracy, in which case you're back to needing a third party.
    - seba_dos1 3y ago
      I've been working on a phone that didn't have well-integrated AGNSS and used MLS for WiFi and cellular-based location when it didn't have GNSS fix. I'm perfectly aware that what you're saying is technically true, but try to explain that to the users :P From the user perspective, it's not going to be a good experience if you rely on cold GNSS only on a mobile device (unless the user is already well aware of what to expect and how to behave).
seba_dos1 3y ago
Fun fact: almanac and ephemeris data that makes (at least basic) AGNSS work is mostly available publicly, either from agencies that operate the constellations or from observatories worldwide. After reverse engineering the expected format I was able to feed the module I worked with with fresh data without having to use the proprietary (and unreliable) AGNSS service it came with.

dgacmu 3y ago

I run a modest fleet of mostly-offline data collection devices that rely on GPS; we pay a lot of attention to how long it takes before they can sync. With a good sky view, the GPS chip often has a 3D position lock before Linux has finished booting. What you're seeing is the effect of AGPS and the interaction with the phone's aggressive power management. https://en.m.wikipedia.org/wiki/Assisted_GNSS https://en.m.wikipedia.org/wiki/Assisted_GNSS It's not really a limitation of GPS, it's about using the external service to let you minimize the time your GPS receiver is active. You can get a great fix without AGPS, but you can't both keep the GPS off 99.9% of the time _and_ get a fast, great position fix.

jeroenhd 3y ago
Fair enough, I suppose. I think in the context of smartphones, continuously operating the GPS chip is simply not an option, but in other types of devices that isn't as big of a problem.
seba_dos1 3y ago
> You can get a great fix without AGPS Yes, after waiting minutes with good line of sight for almanac and ephemerides to download from the satellites. Anything that gets a fix faster is already "assisted", usually either by fresh data downloaded online or not-yet-fully-out-of-date data stored locally.
- dgacmu 3y ago
  Sure. I was simply observing that this phrasing: > but you certainly can't get a good fix without an external party. is not true. You can get a great fix without a third party. You just have to be more patient for your TTFF. * Unless you want RTK-level accuracy, in which case you're back to needing a third party.
  - seba_dos1 3y ago
    I've been working on a phone that didn't have well-integrated AGNSS and used MLS for WiFi and cellular-based location when it didn't have GNSS fix. I'm perfectly aware that what you're saying is technically true, but try to explain that to the users :P From the user perspective, it's not going to be a good experience if you rely on cold GNSS only on a mobile device (unless the user is already well aware of what to expect and how to behave).

seba_dos1 3y ago

Fun fact: almanac and ephemeris data that makes (at least basic) AGNSS work is mostly available publicly, either from agencies that operate the constellations or from observatories worldwide. After reverse engineering the expected format I was able to feed the module I worked with with fresh data without having to use the proprietary (and unreliable) AGNSS service it came with.