Working on Apple's iBeacons, here is some code that I use to initialise CLLocationManager and start monitoring for beacon regions:
self.locationManager = [[CLLocationManager alloc] init];
self.locationManager.pausesLocationUpdatesAutomatically = false;
self.locationManager.allowsBackgroundLocationUpdates = true;
self.locationManager.delegate = self;
How much does pausesLocationUpdatesAutomatically play a part in region monitoring?
The official documentation says:
A Boolean value indicating whether the location manager object may
pause location updates.
However the "Getting Started with iBeacons" official guide does not mention this. Plus it was last updated in 2014 and I haven't found any more on this.
How does this affect battery life?
How does this affect the iBeacon region detection?
Location updates and beacon detection are not related.
iBeacon detection uses the Bluetooth chipset and doesn't provide you with a location as such. It just tells you that you entered (or exited) a CLBeaconRegion.
CLCircularRegion detection is different; this relies on determining the user's latitude and longitude; either by GPS or WiFi. GPS has a significant impact on battery life.
So, the short answer is that pausesLocationUpdatesAutomatically shouldn't have any impact on beacon detection.
If you check full description for pausesLocationUpdatesAutomatically in documentation, you'll see explanation:
Allowing the location manager to pause updates can improve battery
life on the target device without sacrificing location data. When this
property is set to YES, the location manager pauses updates (and
powers down the appropriate hardware) at times when the location data
is unlikely to change. For example, if the user stops for food while
using a navigation app, the location manager might pause updates for a
period of time. You can help the determination of when to pause
location updates by assigning a value to the activityType property.
And for activityType:
The location manager uses the information in this property as a cue to
determine when location updates may be automatically paused. Pausing
updates gives the system the opportunity to save power in situations
where the user's location is not likely to be changing. For example,
if the activity type is CLActivityTypeAutomotiveNavigation and no
location changes have occurred recently, the radios might be powered
down until movement is detected again.
If you turn on pausesLocationUpdatesAutomatically it'll start to monitor significant location changes and save battery since it is not using GPS so often.
Region detection, in such case, will occur when there is significant change, so this check will be performed less often, tricky part here is how much is region detection important for you - if you decide to save battery will significant change detection be ok for region detection.
I hope this helps.
Related
I want to get the different locations of the users in order to display him the trips he did. But in order to save my user's battery, I want to get his location just every 10 seconds with my CLLocation manager.
I first thought about not implementing the 10 seconds interval and get the user's location every time he move with the didUpdateLocations of the CLLocationManager, but when I simulate a drive I get new location every second and I think this is really bad for the battery, am I right ?
Do not try to second guess the location manager. Your job is to set its properties appropriately, such as distanceFilter, desiredAccuracy and activityType. Apple will use every trick in the book to keep battery usage reasonable given your settings. As the docs tell you:
Core Location manages power aggressively by turning off hardware when it is not needed. For example, setting the desired accuracy for location events to one kilometer gives the location manager the flexibility to turn off GPS hardware and rely solely on the WiFi or cell radios, which can lead to significant power savings.
If the goal is track location in the background, there are special modes for that, which save even more.
Check location every 10 second a lot frequent, it will be drain user's battery too fast.
If you would save battery, you should learn apple guide about location manager.
You need use distanceFilter and desiredAccuracy
Base guide CLLocationManager
Energy Efficiency Guide for iOS Apps
Location Awareness Programming Guide - Tips for Conserving Battery Power
Update
Also you can check how fast user moving CLLocation have speed and adjust activityType
I want to track the user location in background, in the purpose to show him an alert when he is close to one of his friend.
So i start with CLLocationManager. As far as i know their is only one reliable way to let the app know about the location update even if the user reboot the Iphone or kill the app: startMonitoringSignificantLocationChanges. But the problem is that even inside a city with many wifi, startMonitoringSignificantLocationChanges fire the DidUpdateLocations when the user move around 1km and that is really too much for my need
on the other way startUpdatingLocation is firing DidUpdateLocations at good interval (even too much because even when the user do not move it's fire quite often DidUpdateLocations). But startUpdatingLocation not survive to iphone reboot or app being killed by the user. Also I suspect that even with an accuracy of 100m, startUpdatingLocation use lot of battery consumption.
So the question: What strategy i can use in my app to track efficiently without draining too much the battery the user location at full time? I need an accuracy of around 100m and if possible an interval between 2.5 - 5 min for each track (i didn't find any option to specify a delay to wait before to catch a new location)
Actually i think to do something like this :
2 locationManager, 1 GPS and 1 Significant Changes
when app start I do with significantChangesLocationManager: startMonitoringSignificantLocationChanges and startMonitoringVisits
I also call GPSLocationManager startUpdatingLocation to retrieve the accurate user position. I set up PausesLocationUpdatesAutomatically(true) so that the GPSLocationManager will stop by himself soon or late
on DidUpdateLocations raise by the GPSLocationManager I start monitoring region enter/exit (100m radius around the obtained latitude/longiture) with significantChangesLocationManager
What do you think of such strategy ?
Even though you will receive more triggers than you need, as you already said, you can use startMonitoringSignificantLocationChanges. It is implemented in a very energy efficient way. It allows the app to be terminated and only be woken up again when iOS thinks the device has moved significantly. Another advantage would be that your app doesn't need the location background mode, which could raise questions during an app review.
The startUpdatingLocation let's the app continuously update the location of the device, even though you only receive a couple didUpdateLocations: events. Also, iOS cannot shutdown the app while updating is active, so it consumes a lot of battery.
You can also consider geofencing, with an exit geofence around the current location. However, significant location updates will be more reliable. Exit geofences won't trigger anymore once you're already out of a geofence, which could happen when the phone is turned off inside a geofence and turned back on outside. This solution has the same advantage of not needing a background mode.
As far as I understand your use case, startMonitoringSignificantLocationChanges sounds as the best option. You won't have control over the exact time interval and distance it triggers, but it is very energy efficient and easy to use.
As mentioned in comments, here are some approach I had to do in order to get the expected result in our app.
Significant Location Updates - is good to wake your app up once it gets finished by some reason that you can't control, so even if you lose some points, it will get back in some seconds/minutes.
This is not good if you need a good accuracy, as you cannot control the distance / time or whatever, iOS will update locations when mobile antenna is changed, wifi connection, turn air plane mode off and on but will not give a sequence of gps points.
Start Location Updates - Best accuracy but battery drainer. So you can't just turn it on let it go. You must implement some controls over it.
Background tasks - The only way I've found to keep my app alive.
The way you can combine is:
Have 2 location managers isolated, one for significant location change and one for start updating location;
Start your app with both turned on;
Inside your didUpdateLocations you can create your logic to start and stop your background tasks;
Create methods to start and pause your location manager and create your timers to control that;
inside your bg task you will start or pause your update locations, but never stop it, just if for example, your user logs out and you want to stop location;
keep significant location update location manager alive forever, if for some reason iOS decide to kill your app when in bg, it will ensure that in a given moment your app will come back to life;
For battery live, try do not use kCLLocationAccuracyBestForNavigation for accuracy as when it starts it eat a LOT of resources, most of time, kCLLocationAccuracyBest is more then enough and if you can use kCLLocationAccuracyNearestTenMeters;
Your didUpdateLocations will give you mostly a bunch of points, try to get only those with good horizontalAccuracy, around 20 meters for us was good enough, so let it work and once you have a point with good accuracy, you can pause it again.
Below you have some links that helped me a lot to implement our solution, none of those have a "as is" solution, as I said, I had to mix all of them and test a lot to understand its behaviour and make the necessary adjustments.
https://github.com/voyage11/Location
http://mobileoop.com/background-location-update-programming-for-ios-7
http://zaachi.com/2013/09/30/ios-locationmanager-location-update-in-my-own-interval-with-application-in-the-background.html
In addition to Mark's answer I would like you to explore pausesLocationUpdatesAutomatically which can help you save battery from draining when user has stopped Apple Documentation
Allowing the location manager to pause updates can improve battery life on the target device without sacrificing location data. When this property is set to true, the location manager pauses updates (and powers down the appropriate hardware) at times when the location data is unlikely to change. For example, if the user stops for food while using a navigation app, the location manager might pause updates for a period of time. You can help the determination of when to pause location updates by assigning a value to the activityType property.
I am using Core Location for turn by turn based navigation and would like to show a "GPS lost" alert in tunnels.
The problem is that the following two scenarios look the same to the app:
The user drives into a tunnel. GPS updates cease because there is no way to know where the user is.
The user stops at an intersection. GPS updates cease because the user is no longer moving.
I need to set these two situations apart. Ideas?
I have tried looking at the horizontalAccuracy property, but sometimes the updates cease completely, so there is no new horizontalAccuracy information.
Normally with CLLocationManager set for best accuracy for navigation and no distance filter, you should get a location update once a second even if you are stopped at an intersection.
If you stop getting those updates while the motion coprocessor (using CMMotionActivityManager) says you are still driving then you can infer that you are in a tunnel (or underground car park or someplace with a bad GPS signal).
BTW, GPS updates should not stop when you are stopped at an intersection if you have set distanceFilter = 0 and desiredAccuracy = kCLLocationAccuracyBestForNavigation and activityType = CLActivityTypeAutomotiveNavigation, etc.
Another thing to watch out for, if the tunnel has cellular coverage, you may still get location update from cellular triangulation but with worse accuracy. If the CLLocation.horizontalAccuracy goes from less than 50m to over 300m then you have lost GPS/GLONASS coverage even though you are still getting location updates.
Look at locationManager:didFailWithError: method:
If the location service is unable to retrieve a location right away,
it reports a kCLErrorLocationUnknown error and keeps trying.
To determine a second situation (user stops) use locationManagerDidPauseLocationUpdates: method:
When the location manager detects that the device’s location is not
changing, it can pause the delivery of updates in order to shut down
the appropriate hardware and save power. When it does this, it calls
this method to let your app know that this has happened.
Does DesiredAccuracy property affect region monitoring ? My guess is that it just affects location updates, but I want to be sure. Apple documentation doesn't specifically say anything about that.
No, it won't affect region monitoring.
But a delay may be observed based on which source the framework fetched the location updates.
Setting a desiredAccuracy property will enable LocationFramework to provide you location updates & significant location changes based on the property. If you choose it to be a value "best", the framework will take care of sending location updates as per that value, depending on the location updates being fetched from either wifi, or cellular or GPS.
If you set it to "navigation", you will get location updates from all the possible ways the framework can detect the location changes.
Hope that helps.
I'm building a little prototype app to test Location Services. My app uses both -startUpdatingLocation and -startMonitoringSignificantLocationChanges (for background processing).
In both cases, I'm trying to send a json object to a server with the location data I get, but I'd like to be able to also send some sort of identifier so I can determine which mode of location service was used to acquire the data (GPS, wifi, tower or at least if it was through one of the two services above.
I'm setting up my CLLocationManager in the AppDelegate if that makes any difference.
Thanks
The sources that CLLocationManager uses are not provided. However, you can determine whether GPS is allowed to turn off by setting the desiredAccuracy property. As the documentation notes, an accuracy of 1 kilometer may have the GPS turn off.
For example, setting the desired accuracy for location events to one kilometer gives the location manager the flexibility to turn off GPS hardware and rely solely on the WiFi or cell radios. Turning off GPS hardware can lead to significant power savings.
You don't exactly control the GPS because other apps may be requesting a greater accuracy in the background.
You can roughly guess what was used for determining your location by examining your CLLocation object. Each CLLocation object has a property called horizontalAccuracy. This value is measured in meters. If it is less than 1 kilometer then GPS was probably used.