offline maps & mobile battery life

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neilus 25 Jun 2014
Hiya
Just a quickie: I use the runtastic app for mtb-ing and a cool feature is that you can download maps to the phone so they dont need to load via your network.
Do you think this would save valuable battery life?
Cheers
Neius
 wilkesley 25 Jun 2014
In reply to neilus:

Best way to save battery life is to put your phone into Flight Mode. That turns off all Phone radios/WiFi. Second best tip is not to turn on the screen, but that's a bit of a Catch 22 if you are using it for navigating.
In reply to neilus:

> Do you think this would save valuable battery life?

Well, it will stop your phone needing to access the internet to fetch tiles, so, yes, it should reduce the power use. And give you a much better response when scrolling the map than trying to rely on 2G or 2.5G data (you're unlikely to get 3G away from towns).

As wilkesley says, it will allow you to put the phone in flight mode, therefore turning off the RF subsystem. Although if your phone is an iPhone, you may find that this kills the GPS receiver, too... Certainly, turn off wifi and bluetooth if you're not using remote sensors that need them.

If you have an Android phone, look at the detailed power usage to see what's using it (and recommendations for saving power). The display will probably feature quite highly if it's turned on a lot.
neilus 25 Jun 2014
Thanks for the info guys...yeah airplane mode kills the gps but that was my thinking, that having to constantly load maps with lots of zooming in/out, scrolling etc would drain the battery...im not sure if the iphone has a cache for images that it would use once its been viewed.
Ill have a tinker and see how i get on...
Cheers!
In reply to neilus:

> im not sure if the iphone has a cache for images that it would use once its been viewed.

That will be down to the mapping program you use, not the iPhone. What program are you using? The easy way to test if it supports cached maps is to put the phone in airplane mode, and see if you can still see and scroll about maps... You'll only be able to see tiles that you've cached (i.e. actively downloaded by viewing), of course. Some mapping apps allow you to download an entire section of mapping, although that usually violates terms & conditions of the mapping sources. Some apps have been leant on to remove such 'map creation' modes.

 RomTheBear 27 Jun 2014
In reply to neilus:
> Thanks for the info guys...yeah airplane mode kills the gps but that was my thinking, that having to constantly load maps with lots of zooming in/out, scrolling etc would drain the battery...im not sure if the iphone has a cache for images that it would use once its been viewed.

Airplane mode doesn't kill the GPS on iPhones. It just makes getting an initial fix a lot slower (sometimes up to a minute) because the phone can't use your broad position approximation from phone masts to accelerate the fix, once you get the fix though, the GPS will work fine.

Now if you use a mapping program which allows you to store maps offline, do so and put the phone in airplane mode, you will save a lot of battery life, but the most power hungry component in your phone is the screen so keep brightness down and turn it on only when needed.
Post edited at 13:22
In reply to RomTheBear:

> Airplane mode doesn't kill the GPS on iPhones.

It would be nice to think that the iPhone only uses network connection to get A-GPS ephemeris and almanac, but I've seen some detailed hardware teardown sites that discuss the various chipsets, and the different builds for different network operators. And, of course, there have now been umpteen versions of the iPhone, and sense may finally have prevailed.

I don't own an iPhone of any sort, but I'll be very happy if someone can confirm that their version of the iPhone will get a fix using just the GPS function, either by getting A-GPS data from the network first, and then turning off all other RF (airplane mode, WiFi and Bluetooth), to see if the GPS still tracks position, or by turning of all RF and waiting for a cold or warm start. You'll need to turn off Wifi because it will still provided an estimated position from Wifi basestation signals and their logged locations. And, in a dense Wifi environment, that estimate can be pretty good...
 RomTheBear 27 Jun 2014
In reply to captain paranoia:

> I don't own an iPhone of any sort, but I'll be very happy if someone can confirm that their version of the iPhone will get a fix using just the GPS function, either by getting A-GPS data from the network first, and then turning off all other RF (airplane mode, WiFi and Bluetooth), to see if the GPS still tracks position, or by turning of all RF and waiting for a cold or warm start. You'll need to turn off Wifi because it will still provided an estimated position from Wifi basestation signals and their logged locations. And, in a dense Wifi environment, that estimate can be pretty good...

Actually I was wrong, I just started from a cold start in airplane mode and you can't get a GPS fix, at least on my iphone 4S.
neilus 28 Jun 2014
Wow what a knowledgeable bunch you are! Ok firstly the app is runtastic mountainbike which as i say allows you to download maps. It doesnt appear to cache maps as nothing except the sections ive downloaded appear in airplane mode. Its a great app if only for the open cycle maps which are fantastic - they show every kind of trail/track and topography as well.
As an experiment I booted up the app and got a green gps icon, then switched on airplane mode to see if it could maintain tracking. The icon stayed green leading me to think it was working...but aparently i was stumbling round an area about 2 miles from here like a drunken daddy long legs...
So im still not really any the wiser what connections are needed to use gps tracking - my gut feeling is that even if the cellular data is deactivated, as Captain Paranoia said, wifi would make it work. Bu if im 10 miles deep in the forest, surely im too far from any wifi hotspot for it to work??
Cheers!

 Glyno 28 Jun 2014
In reply to captain paranoia:

without hijacking the thread, can I just ask... does the GPS work on an Android phone when in Airplane mode?
 Ben07 28 Jun 2014
In reply to Glyno:
Yeh it does.
.
> without hijacking the thread, can I just ask... does the GPS work on an Android phone when in Airplane mode?

 Glyno 28 Jun 2014
In reply to Ben07:

splendid. thanks.
 Ridge 28 Jun 2014
In reply to Glyno:

To confirm what benlatham said, yes. I think it's only iphones/ipads that have that annoying little feature. Just check and both my old samsung s2 and new xperia z1 still have a functional gps in airplane mode.
neilus 28 Jun 2014
In reply to Ridge:

Yes but does it actually work? See my comment above; thought my iPhone was working until i tried to track my route around the local market - epic fail!
 Jack B 28 Jun 2014
In reply to Ridge:

With android it varies from phone to phone. Mostly it depends on how much the manufacturer paid for the GPS chip, and how much effort they put into the drivers.

It all hinges on how the phone knows where the satellites are, information which is known as an almanac and ephemeris. GPS sats transmit this information all the time, but it repeats fairly slowly - it may take 10 minutes to get all of it. If a data connection is available, the phone can download it from the internet instead.

On my moto defy, for example, I get a fix in seconds if I have a data link. If I haven't got a data link, but have had one and had the GPS on in the last hour, then it uses cached data and gets a fix in a similar time. If more than an hour has passed, then for reasons known only to motorola it forgets the data and won't get a fix for 3-4 minutes, if at all.
In reply to Glyno:

It depends on the phone, I think. Some models use a GPS function as part of their RF chipset, so when that's off, you may not get GPS.
In reply to Jack B:
The lifetime of the ephemeris data is pretty short; 4 hours IIRC, so your Moto should be able to do a warm start within this period. But it may not store the ephemeris...

The repeat rate for the ephemeris data is 12.5 minutes, so that ought to be the maximum time to perform a cold start. It should be quicker than that if it can do scatter-gather load from multiple satellites in view.
Post edited at 16:42
In reply to neilus:

> my gut feeling is that even if the cellular data is deactivated, as Captain Paranoia said, wifi would make it work.

WiFi will only allow it to get the A-GPS data, and do crude position from WiFi hotspots. If disabling the cellular data connection also kills the GPS receiver, you will not get a GPS fix, no matter how many WiFi hotspots you can see. And, yes, the range of a WiFi hotspot is no good outside an urban environment.
 inboard 01 Jul 2014
In reply to neilus:

One way to get around this is to set a SIM PIN, then when you want to use your iphone for navigation (but not phoning), you can switch the phone off, back on again, and not put in the PIN. This seems to prevent the phone bit working, yet the gps is absolutely fine. Still chews up battery life but not so badly...
neilus 01 Jul 2014
Thanks for all the replies, useful info...amazing that we use this stuff every day yet numpties like me dont have a clue how it works!
Did about 35km on my mountainbike today, used runtastic mtb app and used the downloaded maps with cellular, wifi and bluetooth (not that i ever have that on) all switched off and it worked ok, somehow...it drained about 10% of the battery per hour which is ok and better than before! I also switched the sceen brightness down to about 60%, I pretty much have it like that all the time now - 100% brightness is just blindingly bright and totally unneccessary...

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