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I had an interesting experience recently that I think summarizes this whole problem. I was in another city and rented a car and it came with navigation. I kne

by bvinc 10y ago

I had an interesting experience recently that I think summarizes this whole problem. I was in another city and rented a car and it came with navigation. I knew I could just use my phone, but I decided to use the navigation that the rental car came with, just for fun. 1. First, I knew the name of my hotel, but not the address. I tried to search the business directory. I had to input the CITY AND STATE, which is painfully slow on the pressure-based touch screen, but I did it and did a search. I couldn't find it. 2. So I took out my phone and found the address and went back to the navigation in my car to type it in. 3. I slowly input the city and state again before it lets me input an address starting with the number. 4. When it came time to pick the street name, it was ambiguous. There's one street name that looks right. There's another with a W in front of it. There's another highway number that could also be it. I pick one and I can tell it's not in the right spot. Now I have to start all over. 5. I start all over, input the city and state and address and I think I have it right. I start to navigate. 6. It can't find a GPS signal. Maybe it's the parking garage I'm in. Maybe it just takes a while. I sit there. I'm about 10 minutes in and I still haven't gotten any navigation instructions. 7. I get nervous because I won't even know what direction to turn when I leave the parking garage. I take out my phone and say "Ok google, navigate to the blah blah Hotel". It says "Ok, sure" and my phone has no problems finding GPS and I have navigation instructions pulled up in about 5 seconds.

otempomores 10y ago
You forgot the voice command excuse machine in every car. Im sorry.. I still did not understand...goodbye.
dingaling 10y ago
> and my phone has no problems finding GPS and I have navigation instructions pulled up in about 5 seconds. That's because your phone isn't actually using GPS ( e.g. Navstar or Glonass ) at that point, it's using cell triangulation or wifi-based location. For example the fastest possible first-fix with Navstar from a warm-start, using cached prior-location and ephemerides, is 30 seconds[0]. From a cold ( position-unknown ) start, such as a car nav-system powered-down in a parking-lot for an extended period, the first-fix will take longer than 12 minutes. There is no technological way around that, it is an artifact of the system architecture. [0] and that's for a top-end receiver than can sync to four satellites 'simultaneously' using time-division.
- panic 10y ago
  How often do cars change position while powered down? That is, why not always (even on "cold start") use the last known position as a starting guess? How do phones get GPS-quality location data even immediately after being rebooted?
  - dismantlethesun 10y ago
    Annectodatally, I remember that some years ago my phone used to take 5-10 minutes to find GPS whenever I asked for directions. Now adays, it's instantaneous. The software has improved dramatically, using some combination of previously saved location, WIFI triangulation, and dead reconning to figure out a near accurate location to within 50 feet so long as you're in a city. Car navigation systems can do better. They're not even 'pure' GPS services, they have access to mobile cell, they do online updates for maps, and their accelerometers are far better than phones. The software though is simply worse than what Google can provide.
  - maxerickson 10y ago
    Phones do more than use the towers for location information, they use the data connection to download information about the satellite positions, shortcutting a 12.5 minute step: https://en.wikipedia.org/wiki/Assisted_GPS https://en.wikipedia.org/wiki/Assisted_GPS I wonder if the average car system really has the sensors for high quality inertial navigation. If they don't, the navigation won't work very well anyway until it has a decent GPS fix.
- InclinedPlane 10y ago
  A warm start is actually typically faster than 30 seconds, averaging closer to 20 seconds. Additionally, almost all fixes using smart phones are hot starts. This is because smartphones use assisted GPS, they download almanac and ephemeris data not from the GPS network itself (where they are broadcast every 12.5 minutes and 30 seconds, respectively) but over a data network, in seconds. Similarly, smartphones have a pretty good idea of where they are already, because they keep track of their positions historically and they use cell tower triangulation as a secondary location system. From a hot start a GPS receiver could get a fix in only a handful of seconds, potentially.

by bvinc 10y ago

otempomores 10y ago

You forgot the voice command excuse machine in every car. Im sorry.. I still did not understand...goodbye.

dingaling 10y ago

> and my phone has no problems finding GPS and I have navigation instructions pulled up in about 5 seconds. That's because your phone isn't actually using GPS ( e.g. Navstar or Glonass ) at that point, it's using cell triangulation or wifi-based location. For example the fastest possible first-fix with Navstar from a warm-start, using cached prior-location and ephemerides, is 30 seconds[0]. From a cold ( position-unknown ) start, such as a car nav-system powered-down in a parking-lot for an extended period, the first-fix will take longer than 12 minutes. There is no technological way around that, it is an artifact of the system architecture. [0] and that's for a top-end receiver than can sync to four satellites 'simultaneously' using time-division.

panic 10y ago
How often do cars change position while powered down? That is, why not always (even on "cold start") use the last known position as a starting guess? How do phones get GPS-quality location data even immediately after being rebooted?
- dismantlethesun 10y ago
  Annectodatally, I remember that some years ago my phone used to take 5-10 minutes to find GPS whenever I asked for directions. Now adays, it's instantaneous. The software has improved dramatically, using some combination of previously saved location, WIFI triangulation, and dead reconning to figure out a near accurate location to within 50 feet so long as you're in a city. Car navigation systems can do better. They're not even 'pure' GPS services, they have access to mobile cell, they do online updates for maps, and their accelerometers are far better than phones. The software though is simply worse than what Google can provide.
- maxerickson 10y ago
  Phones do more than use the towers for location information, they use the data connection to download information about the satellite positions, shortcutting a 12.5 minute step: https://en.wikipedia.org/wiki/Assisted_GPS https://en.wikipedia.org/wiki/Assisted_GPS I wonder if the average car system really has the sensors for high quality inertial navigation. If they don't, the navigation won't work very well anyway until it has a decent GPS fix.
InclinedPlane 10y ago
A warm start is actually typically faster than 30 seconds, averaging closer to 20 seconds. Additionally, almost all fixes using smart phones are hot starts. This is because smartphones use assisted GPS, they download almanac and ephemeris data not from the GPS network itself (where they are broadcast every 12.5 minutes and 30 seconds, respectively) but over a data network, in seconds. Similarly, smartphones have a pretty good idea of where they are already, because they keep track of their positions historically and they use cell tower triangulation as a secondary location system. From a hot start a GPS receiver could get a fix in only a handful of seconds, potentially.