I am trying to create a low-power watchOS app that will only periodically (every 5 minutes or so) need an updated but precise location. The key word there is need. The app certainly could provide better information if it were getting location updates consistently but the goal is for this app to be low power. That being said (and I am not sure if this is possible) if another app is constantly streaming location in the background it would be nice to get those updates too if that does not have extra battery cost.
Is there a way to only request location periodically? Is this actually better for the energy impact of the app?
Related
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
What I want to do:
I want to have my iPhone to frequently (formally defined later) upload my GPS location to a central server. I want to do this in the most battery efficient way.
Research I'm aware of:
Apple Documentation:
https://developer.apple.com/library/ios/#documentation/CoreLocation/Reference/CLLocation_Class/CLLocation/CLLocation.html#//apple_ref/doc/uid/TP40007126
Stack Overflow Links:
Response 1
Response: proof of existence; some other tool can do it
How to reduce iPhone battery consumption while using GPS
Response 2
Response: track only cell tower changes
iPhone GPS - Battery Draining Extremely Fast
iPhone running periodical process in the background - battery optimized way
Question
My question is a bit vague in that my definition of "frequently" is really dependent on what the battery life can tolerate. For example, if the battery can take updates of every 5 minutes, I'd like to do it every five minutes; if the battery could do this every 10 seconds, I'd like to do it every 10 seconds.
I really want to understand
the different ways (change on significant location, timer, background?) continuously uploading GPS locations can be implemented
advantages / disadvantages
approximately how long the battery life can last in each case
This seems like a fairly generic and common problem. Does anyone know of either:
an in depth analysis of the various methods
or if there is a single "optimal" way to do this?
[Moderators: feel free to mark this comment wiki. I'd love to just get lots of different answers + cost benefit analysis of them.]
Have a look at the Apple Documentation Here.
The significant-change location service offers a low-power location service for devices with cellular radios. This service is available only in iOS 4.0 and later and can also wake up an application that is suspended or not running.
It all depends on the use case. If the user will stay at a certain location and all you want to do is to track if he is leaving the country, tracking the significant location changing will be most suitable. However, this will not be precise enough for navigation apps.
One advantage of choosing the "Apple-Algorithm" is that they'll optimize it for you, if battery issues occur. (-:
I would like you to give me your feedback on which method consumes less battery.
My app will run in the background and will wake up with location changes, so I would like to use the method that consumes less battery.
Any ideas on which one it is?
Thanks
Neither of these choices is responsible for more or less battery consumption.
In order for your app to be notified of any location update, regardless of whether it is for a region change or a significant location change, you must specify in your app's Info.plist file that you will require location-services in the background.
There are actually two relevant choices for location services: location-services or gps.
In order NOT to drain the user's battery, choose location-services. If you say your app needs gps background services, you WILL drain the battery because this will cause the GPS hardware (assuming it is present) to be enabled, and THAT is the cause of battery drain. When you specify location-services, the device uses the cellular radio (which is on anyway, assuming you have an iPhone) to pinpoint the location instead. Not as accurate as gps, but most apps don't need GPS accuracy. (If you do, then use gps, of course, but know the consequences vis a vie battery life.)
I recently wrote a test app all about this (and I wrote about it last week here) and what I found was there was no significant battery drain when I had several regions setup for monitoring and I specified location-services as a required background service.
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.
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.