I want to create an (game based) iPhone application which sends your GPS location on a specific time (like 3-5 times a day) to a server. I found an apple page explaining some functionality to run in the background like location, music and VOIP.
I need the GPS to be accurate on the meter.
Can someone help me with a small example?
It really depends on your usage of the location. If you monitor actively, kiss the battery of your user goodbye. Very detailed accuracy, even bigger hit to battery. The backgrounding of location is all or nothing as far as accuracy goes.
Less hit, less accuracy is -startMonitoringForSignificantLocationChange. May not be accurate enough for you.
Better depending on usage, region monitoring. Triggers event on entry or exit of defined region.
You don't have the benefit of accuracy and timed location based events. You can do it, but is going to require a lot more effort on your end.
While this is untested, I am planning an app with a similar need. My solution is that on a significant location change, the app will determine what interval exists between the update timestamp, and when I care to know the users location (5pm for instance). If that's below some threshold, it will go into startUpdatingLocation mode (full power, battery draining, which is why that threshold is important) and then, on each location update, check if that target time has passed. if SO, send the update to your server, and go back to monitoring for significant changes. The catch is that if it still requires some movement to trigger the significant change update...so it isn't a perfectly reliable solution, but it may work depending on how you're using the data
You can't "schedule background work". iOS doesn't allow it.
The solution is to set yourself up for notification on significant change (which is some hit to the battery, but it's not horrible), and then only DO anything with that at occasional intervals.
Related
Some of my users ran into an issue where they couldn't fetch the location using Location Service.
In the screenshots they sent me, i noticed that the battery level was really low, like 2-5%.
My question is, does iOS stop the location service when the device is running out of battery?
Thanks
Enabling Low Power Mode (the one that turns the battery icon yellow) does several things to reduce the battery usage of your device. This probably includes the accuracy and refresh rate of the GPS.
If you're requesting a location with a high level of accuracy, the system might either take too long and timeout or just decide not to fulfill that request since the hit on the battery would be too much.
does iOS stop the location service when the device is running out of battery
It certainly might. The GPS is one of the highest power draws of all the sensors. Turning it off would make a lot sense. See also Apple's own statements about low power mode:
https://support.apple.com/en-us/HT205234
Note that if this is the case, it would hardly be an issue with your app. Your app might use a lot of battery, which could be a problem; but if location services itself is affected, all map/navigation apps would be affected.
I am trying to set up an app that will be able to check people's locations in the background, see if they are at a given location, and send a ping to a server if they are. We do not want to drain the energy of our users, so we are attempting to figure out the best solution.
I've done substantial reading and I have not found very much information on these methods. I'll go through the pros and cons as I understand them right now
startMonitoringForSignificantChanges
Description: Based off of wi-fi and cell tower changes the system wakes up the app.
Docs:
Apps can expect a notification as soon as the device moves 500 meters
or more from its previous notification. It should not expect
notifications more frequently than once every five minutes. If the
device is able to retrieve data from the network, the location manager
is much more likely to deliver notifications in a timely manner.
Pros:
Most battery efficient
Cons:
Dependent on wi-fi/cell tower changes
Can only assume that this will be called every 200m to 2km (if not more in certain areas)
More on accuracy
Thus, inconsistent and imprecise
10-minute start-updating or "n-minute updating":
Description: This basically asks the app for more time, when that extra time is about to expire, it calls [self.locationManager startUpdating], grabs the location and extends the background thread for 10 more minutes.
Pros:
Consistent
Can be as accurate as you want it to be as consistently as you
want it
Cons:
Has to do a call every ten minutes or less to keep the app running in the
background (ie n can't be greater than 10 for the calls)
Questions:
What effect does this have on the battery? Does waking up the GPS and shutting it off hurt the battery more? I couldn't imagine running a brief location check in the background would drain the battery that much... but then again, I don't know what goes into powering up the GPS and getting a usable signal.
startMonitoringForRegion (geo-fencing):
Simply put, your app gets woken up when you enter into a pre-defined region. This is the oddball of them, it is more recent and there is less documentation on it. I can't find a good description on how the "system monitors" the boundary crossing. For all I know it is some really smart algorithm, or they are constantly pinging the GPS which would make it less effective than the other methods for doing this.
Pros:
Simple implementation
Managed by the system so you don't have to invent your own ad hoc geo-fences Only triggers on boundary crossing... no unnecessary data to just throw out in exchange for a battery hit
Thus, should be the best for this sort of thing, accurate, managed by the system
Cons:
People question its effectiveness
Huge conflicts on whether or not it is good for battery life or if it
drains battery life terribly.
How is the system monitoring this!?
Basically, indeterminate behavior.
I guess my question boils down to how does startMonitoringForRegion: compare to these other methods of testing user location in the background when it comes to battery life, consistency, and precision. Has anyone thoroughly tested this? Or used it in their app and gotten at least some feedback? Likely, for my purposes, the trade-off is between geo-fencing and the 10 minute update method. (Also given what Apple has publicly said about iOS7 there will be some background tasks... will this change the calculus for the trade-off between these two methods?) Does anyone have an idea of how these two compare?
Thanks so much! Looking forward to seeing if we can get to the bottom of how to compare these methods.
I've been working on vehicle tracking using GPS for 2 years. Learned a lot the hard way... In my experience startMonitoringForRegion or Geo-fencing depends upon cell change events, didEnter or didExit events doesn't fire up until there is a cell/wifi change event. So it doesn't make any difference w.r.t battery consumption. However it does extra computation which depends on how many regions currently are being monitored. Even Apple's Reminder app doesn't give good results for location based reminders because it uses geo-fencing.
The other approach starting GPS for n minutes after each m-minutes is good option, it should not affect the battery life, if done wisely. What exactly effect the battery is constant GPS activation in high precision mode. Like for instance If you enable GPS with kCLLocationAccuracyBest and distance-filter = 0, you can literally observe battery drainage and soon your device will also start getting hotter.
If I was you, I would go for activating GPS after every 10 minutes for 5 sec with kCLLocationAccuracyBest (or may kCLLocationAccuracyNearestTenMeters to use less battery, if accuracy is not that much important) and distance-filter = 5 (meters). Battery consumption in this case will be unnoticeable. You can play around with similar settings which can address your specific case and finally find out what is best you.
BTW: iPhone uses AGPS, A-GPS additionally uses network resources to locate and use the satellites in poor signal conditions. So, when you do startUpdatingLocation it will also use nearby cell tower information. see http://en.wikipedia.org/wiki/Assisted_GPS
I'm building a location-based app, but I hate having the location services icon on. I only need coordinates once per hour, but I can't figure out how to do this without saying the app is a VoIP app. Is it possible to do this in a way that's App Store acceptable?
You can use location in the UIBackgroundModes of your app, see the documentation.
About the location services icon on, I think you should leave it. It's a fair feedback for your user. A user has to know its position is being tracked and leaving the icon on for a few seconds each time the geolocation actually happens wouldn't be fair. (and it sounds like a case of app rejection to me).
As long as you don't have a negative impact on the device battery, the user will be grateful you let it know you're tracking his position.
For instance, apps such as OpenPaths made my iPhone show the location icon on all the time and have no real negative impact on the battery.
I would register for significant location change updates. When updates happen compare timestamp with last update. Use update if time delta > 60 minutes. Worst case: I believe you get the location indicator outline. this tells the user that a kind of tracking is happening — but not all the time, so it' not a battery issue and you don't get too many support requests. Best case: Registering for significant location change update doesn't show the indicator outline. But I am not certain. Completely without icon might just not be possible.
I want to run a specific task in the background. This task takes few seconds to complete (it writes some GPS location data to a file). This task should run once every 1 hour.
As I understand from the SDK, I do not have a way to INITIATE something in the background unless I run Location Services forever. When this service runs, it gives me an event from time to time, and I'm able to run my code during these calls. I tried it, and even with the minimal precision possible, my battery goes down very quickly.
So, I'm looking for a way to run Location Services for few seconds every hour. All the rest of the time I do NOT want to run Location Services and I do NOT want to use the battery.
Can you help here please?
Thanks,
Gena
What do you actually want to know every hour? Are you trying to determine the location accurately, or just determine if the phone has moved significantly? startMonitoringSignificantLocationChanges will notify you when the phone moves "significantly" (which generally means changing cell towers). In cities this can happen quite often. startMonitoringForRegion:desiredAccuracy: will only notify you when you move outside of a given radius.
startMonitoringSignificantLocationChanges is pretty cheap. It mostly relies on the cell antenna, which is generally on anyway. If it fires more than once an hour, you could always just skip processing and return. But there's no guarantee that you'll be called once an hour, particularly in rural areas.
If you are a VoIP app, then you may register a periodic "checkin" interval when you may run code. But you cannot do this for location apps.
Have you profiled your code using the Energy Diagnostics instrument? What's actually eating time and power? Are you chewing on the radio, the CPU, the disk?
EDIT
When the app dies, Significant Changes still continue to run and leave a small direction arrow icon next to the percentage on the top toolbar of the iPhone. My users complain that the icons remains after killing the app
After the app dies, if you were registered for significant changes, you would expect to be relaunched in response to them. If you want to unregister in cases where you are terminated, you can add stopMonitoring... to your applicationWillTerminate: method. This isn't guaranteed to be called, but it is a good thing to do, and I believe it will be called if the user terminates you directly and you were not suspended (haven't tested that).
Again, significant location changes should be extremely cheap in terms of battery life as long as there is cell coverage. They should not force the GPS to stay on.
Your best bet is to use significant location changes ... here are some links you can get help from -
http://developer.apple.com/library/ios/#documentation/CoreLocation/Reference/CLLocationManager_Class/CLLocationManager/CLLocationManager.html
http://www.switchonthecode.com/tutorials/getting-your-location-in-an-iphone-application
http://longweekendmobile.com/2010/07/22/iphone-background-gps-accurate-to-500-meters-not-enough-for-foot-traffic/#more-480
Question: Does the Significant Location Change background service drain battery easily? I'm trying to track longitude latitude readings when the there is a Significant Location Change. However, before starting, I just want to make sure that this doesn't drain the battery.
If the Location service described above does not drain battery, can someone recommend a way to store the location changes that would be battery efficient. My initial thought was to store the longitude latitude points locally on iPhone and then send the information to the server on a much less frequent basis (2 hours). Anyone have a better approach?
I'm trying to build a simple location tracking app that is battery efficient. Thanks all.
Significant location changes do not take any extra battery draining because the device uses information that the GSM system is working with anyway. It has to keep track of signal strength readings of multiple cell towers all the time anyway. Your app is only started/woken when certain criteria are met.
To conserve battery you have to watch two subsystems:
make sure that CoreLocation is turned off when you don't need it, GPS takes the most
make sure that you send location data to your server in bursts, to allows the transmitter to power down.
2 hrs might be too much because the user might be terminating the app and then the updates would never be made. Or if you implement an offline queue, they would only be sent next time the app is started. But that depends on your specific scenario.
It should be cellular tower triangulation, and not GPS location, which is more than enough for your needs. It shouldn't be battery heavy at all.Same with uploading the location, do it rarely and you are fine.
Edit: Confused Core Location with Significant Location.