GPS on most cell phones uses data connection to download current satellite data in order to decrease the time from cold start to GPS lock. Lack of cell or WiFi can cause GPS to take 5-15 minutes to "search the sky" and download satellite data via low bitrate channel under poor signal conditions.
From cold start. Most starts are not cold. The phone knows where it is, approximately, what time it is (within a second or so, from built-in RTC), and orbital parameters of the satellites overhead (maybe without the latest corrections).
My Garmin watch gets a GPS lock in way less than 5 minutes without any cellular connection.
Actually, your Garmin probably gets A-GPS data uploaded to it via the app.
I think that because Huami/Amazfit/Xiaomi smartwatches already do that. We know this from reverse engineering efforts in Gadgetbridge, but support for Garmin is still new and so there isn't as much info about it; either way it probably works in the same way.
My first GPS Garmin watch used for running back in 2011 didn’t have an app and didn’t have any cellular signal. I put it on my wrist and started running. I don’t remember it taking more than a minute to get a signal.
That’s just not true for modern phones. I use iPhone on hikes without cellular connection and GPS lock is instantaneous. Organic Map app is great for hiking.
You're talking about something very different called a hot start. The GP is discussing time to fix in a cold start scenario. You'd only see this on a phone that had been powered off for months, or "teleported" hundreds of miles away. In this scenario the receiver has to download the new time, new ephemeris data, and a new almanac (up to 12m30s in the worst case) before it can fix. Depending on the receiver, there may also be a delay of several minutes before it enters cold start mode.
If the receiver has recently (last few days) gotten a fix and hasn't moved too much from that fix, it'll be in at least warm start mode. It still needs to download ephemeris data, but this usually takes 30ish seconds to fix.
If the receiver has seen a fix very recently (last few hours) or a recent network connection, it can fix from hot start like you saw, which only takes a few seconds and may not even be observably slow depending on how the system is implemented. Phones go to great lengths to minimize the apparent latency.
The sibling response here covers all of the points I would say. Scott Manley has a nice video covering the history of GPS and how it works, well worth a watch https://www.youtube.com/watch?v=qJ7ZAUjsycY
Yes, much that we think of as Google Maps relies on API calls made to the backend. Plus this assumes that you downloaded the offline maps ahead of time, which in my anecdotal experience is not something that most people really consider. GMaps does (or did at one time at least) have a neat feature of auto-downloading your home area map but, the one time I needed it, it didn't work.
> which in my anecdotal experience is not something that most people really consider
Thankfully I’m in Canada where it’s not impossible to end up in the sticks with no service.
Chewing through your handful of gigabytes/month of data wasn’t hard. Only in the past year or so have double digit gigabyte/month data plans become cost-effective.
And our roaming prices are extortionate, so for jaunts over the border (or internationally), I’ll sometimes go “naked”.
The "Here" app or whatever it is called did offline maps and offline routing decently enough. It wasn't perfect, but it worked for "here to there", even if it didn't find the best possible route.
Carriers have mapping independent of networks. Drivers keep personal GPS too. You would lose traffic and road conditions, I guess, but nothing proper trip planning wouldn't cover.
Do they? I know there are a lot of old units out there but I figure people would have tossed them.
At least I’ve found Waze has been pretty good at starting off with wifi and loading the map of the whole journey after coverage was lost with some resilience for stops/detours.
I am consistently in areas with zero cellular service and I’m reasonably sure Google Maps will route offline. At least, I’ve never switched to another mapping app because I couldn’t route — it’s more usually because Google Maps is more primitive areas is kind of detail-less.
But even if it doesn’t, there are a ton of offline map apps that use OpenStreetMap data.
Google Maps and now Apple Maps (as of ~6 months ago) have offline maps, but not by default. If you enable and download them for your area of interest you can use a subset of the normal app.
I make sure to have this around my usual area and anytime I travel to an area with poor coverage, plus my Garmin watch has offline maps and GPS everywhere, but this is not typical.
Offline maps are a life saver in areas with bad coverage. One of the first things I setup for a new phone or when I’m headed somewhere new on vacation.
This is one of the most interesting differences I often notice between users who rarely leave the city and those who routinely leave. Offline functionality often seems unnecessary at best and absurd at worst to the former group, while the more rural/remote the person the more they value offline functionality. For the most extreme example, talk to the average person who lives outside of Anchorage or Fairbanks in Alaska, and they only really care what the app can do when it's offline as that is it's assumed status when on the go (disclaimer: I moved out of alaska a little over 5 years ago so things might have changed somewhat).
Yeah, if I'm going to travel internationally or if I'm somewhere I know I'll have spotty cell service, I'll download maps. I should probably be better about doing it in local areas where I "assume" things will be fine.
I grew up in a rural area and lived in Colorado for a while. Going home or venturing into the mountains often resulted in bad service so it just became second nature. Good observation!
Lots of people dislike the design choices in OSMAnd, so it's worth mentioning that there are lots of apps that use OSM data and provide offline maps and routing.
agreed. On Google Maps app, there is a feature called "offline maps" which allows a user to select a rectangle on a the map and download all the street info inside it. A whole US state can fit in less than a few hundred megabytes. I have all the city I live in downloaded so I can go on walks without needed to use my data plan.
Anecdotally, I’ve made it to a remote destination using Maps, then hopped back in the car an hour later (with no signal), and it couldn’t load anything. This seems to happen quite often.
Maps used to expire after 30 days (no idea why), and the auto-updating while on wifi wasn't great unless you were in the app forcing it update. Nowadays they last 365d.
worth noting that without cell service, GPS can reliably give you time, lat, long and elevation. So if previously you had no actual map downloaded, or an old or out of date map, you'd just get a pretty accurate dot on an inaccurate map, or just raw coordinates.
