I have an IOS app where I require the user's current location in order to make an HTTP request to get data about nearby locations. Since I just need the user's location once, I am using the CoreLocation requestLocation method. This issue with this is that it takes roughly 10 seconds (which is stated in the documentation). I realize that there will always be a delay which I am prepared for, but the delay on requestLocation is just too long and ruins the user experience.
I was wondering if anyone has thought of a way to get the users location (just once) in a more timely way.
One solution I thought of was perhaps calling the method within the AppDelegate, as the app starts, and then passing the data to the ViewControllers via some shared object. The issue I foresee here is that AppDelegate does complete it's application:didFinishLaunchingWithOptions: function very quickly so I don't think it'll improve my problem
Another solution I thought of could be to use the startUpdatingLocation method, and then use stopUpdatingLocation after receiving the first location. My issue with this is that startUpdatingLocation may also take a few seconds to start up (documentation), so again this may not improve my problem.
The location I get for the user does not need to be super accurate so I am willing to compromise on precision for performance.
Related
We use significant-location-change monitoring to know about our user's whereabouts when the app is not running. This data is based on cellular towers signals and therefore is not very accurate. We would like to use more accurate data whenever it is possible, that is, when the app is active or running in the background.
The question is, should I use "startMonitoringSignificantLocationChanges" and "startUpdatingLocation" at the same time, or, should I switch between those two methods? And if the second option is better, what app delegate events should I use in order to perform the necessary switch?
Unless you want to support a feature that needs continuous high precision location stream, its best to avoid using the high accuracy GPS data via startUpdatingLocation all the time.
I understand from your question that you intend to use more accurate location only at certain points of interest, when your app is woken up. In that case, the second approach of switching-on the more accurate location data only when needed, would be a better idea.
locationManager(_:didUpdateLocations:) in your CLLocationManager delegate would be a good point to start this in your case. Remember that significant location change monitoring API wakes up the system at least once every 15 minutes, even if there are no location changes, until it is explicitly stopped. So one must use it with care.
Instrumenting accurate location tracking while making sure that you don't eat up all of the phone battery is a non-trivial problem to solve. You may want to give third party SDKs like Hypertrack, which specialise in this, a try.
I am working on a app that relies heavily on monitoring user visits in possibly multiple regions / areas. I am currently experimenting with region monitoring which works pretty well, however, the location callback is not as accurate as I want it to be. I have seen CLVisit, but the documentation out there doesnt explain it very well, especially its use.
I think you are misunderstanding the concept of CLVisits. There is actually no Visit object that you need to create. The CLLocationManager delegate method is triggered by the algorithm that apple has determined (see wwdc lecture for more info). This is explained in the CLLocationManager documentation...
Getting the Visited Locations
In iOS, the visits service provides an alternative to the significant location change service for apps that need location information about interesting places that the user visited. For example, if the user is in one location for an extended period of time, the service might generate an event when the user arrives at that location and another when the user leaves that location. The service is intended for apps that might already be using the significant location change service and want an even lower power way to do so. You would not use this service to create navigation apps or apps that rely on regular location updates.
To begin the delivery of visit-related events, assign a delegate to the location manager object and call its startMonitoringVisits method. As the location manager generates visit events, it delivers that information to its delegate’s locationManager:didVisit: method. The event data delivered to your delegate includes only the information that occurred after you started the delivery of events. In other words, if you start the delivery of events after the user arrived at an interesting location, the event delivered by the system when the user departed that location would not reflect the actual arrival time. If the system terminates your app, this service relaunches it when new visit events are ready to be delivered.
That said if you look at this article from NSHipster, it references some current issues with CLVists (for iOS 8.1). It essentially goes on to say that if you want infrastructure that extremely precise don't use CLVisit. Seems like you're doing it right (for now at least).
CLVisit is, as of iOS 8.1, not all that precise. While start and end times are
generally accurate within a minute or two, lines get blurred at the edges of
what is and what is not a visit. Ducking into a corner coffee shop for a minute
might not trigger a visit, but waiting at a particularly long traffic light
might. It’s likely that Apple will improve the quality of visit detection in
future OS upgrades, but for now you might want to hold off on relying on CLVisit
in favor of your own visit detection for use cases where it’s vital your data is
as accurate as it can be.
I am currently saving locations in background. I need latitude, longitude and NSDate which is why I went with CLLocation instead of geopoint. I am trying to figure out how to save locations only every minute or so, as I currently have one element each second.
I cannot use NSTimer as my app still needs to obtain these updates after the authorised delay of running code when in background.
Any suggestion of how this might be done ?
Thank you very much in advance for your help.
Viktor
Make sure you read: Getting the User’s Location,
there are important notes about battery life.
IMO it's better to rely on the framework callbacks and not try to put a timer on it.
You may also consider region monitoring..
Maybe you can give us more details about what you're trying to achieve.
I have a problem in Objective C (writing an app for the iPhone). I know how to use the locationManager and its delegates. Once I called startUpdatingLocation on the locationManager, it will call the delegate method didUpdateToLocation whenever the location is updated. But the problem is, that this way is now suitable for what I want to do. I have a method (in a class) which looks as follows:
#implementation SomeClass
- (someType)getDbContentsOrderByDistance
{
... //here I need the current location
return dbContents;
}
#end
Now this function selects entries from a sqlite database ordered by their distance to the users current location. That is why I need the location in this function. What I want to do in the above method is: get the location, then select the stuff from the database and return it. I know that I could just try to access locationManager.location.coordinate.longitude, but I know that there won't be anything useful inside until the first location update has arrived. And I don't want to start the location updates before (e.g. when starting the app) because that would not be very efficient if I only need the location once.
I know how to do it the way that the delegate is called as soon as a location update arrives. The problem is that I don't know how to get that updated location from there into my method above. Basically I would need to let the method 'wait' until there is the first location update and then continue execution with that location.
Thank you for your help!
The short answer is, you can't. Getting the users location is an asynchronous process, and MUST be an asynchronous process. The device has to fire up various hardware like the GPS, cell tower locator, and WiFi triangulation system, get input from those different devices, and synthesize that into a location. That takes multiple seconds to do.
Putz's suggestion of starting a timer is a good one. I would add a few things however.
Typically the first readings you get from the location manager are really bad and should be discarded. The first reading you get is usually the last location reading when the GPS was active, and will have an out-of-date timestamp. The accuracy reading in that location might appear quite good, but it's a lie. I have seen the first location reading be off by several kilometers. You need to check the timestamp on your location updates and discard any reading that is more than 1 second old.
Once you've discarded the stale readings, the first several location updates are often really bad because the GPS hasn't settled down yet. The horizontal accuracy reading (which is really a "circle of confusion", or radius of possible positions) is an absurdly large value, sometimes a kilometer or more. Again, you need to write your location manager delegate method to discard readings that are too inaccurate. I suggest discarding values with a horizontal accuracy reading of >= 100 meters. How much inaccuracy you can tolerate depends on the specific appellation, but beware of making the accuracy requirement too accurate. Sometimes the GPS refuses to settle down. If you require a 5 meter accuracy, you might not get an acceptable accuracy during the entire run of your app. (If you're in an urban environment, a building, or other area where there is a lot of interference/obstruction of GPS signals)
Once you finally do get a value that's accurate enough, save the location and set your locationAvailable flag to YES.
Note that instead of a timer you could use the notification manager to broadcast a "got a good location" message. Any object that needs location information could register for your notification, and get called when the location manager gets an acceptable location reading.
Start a timer that fires every second or so that calls the function you need the location in. check to see if the location has been set. If the location is valid then kill the timer, if not then let the timer continue and check again in one second or so.
The way of knowing if the location is valid is in the delegate method. Set a global variable like locationAvailable = false. Then when the delegate method gets called set that variable to true.
Using location property can solve the purpose
From apple documentation
location The most recently retrieved user location. (read-only)
#property(readonly, nonatomic, copy) CLLocation *location
The value of this property is nil if no location data has ever been retrieved.
In iOS 4.0 and later, this property may contain a more recent location object at launch time. Specifically, if significant location updates are running and your app is terminated, this property is updated with the most recent location data when your app is relaunched (and you create a new location manager object). This location data may be more recent than the last location event processed by your app.
It is always a good idea to check the timestamp of the location stored in this property. If the receiver is currently gathering location data, but the minimum distance filter is large, the returned location might be relatively old. If it is, you can stop the receiver and start it again to force an update.
Whenever I create a new instance of location manager I get the most recent value of location in location property and since my distance filter is not set , it has the current timestamp. This means I dont have to call startUpdatingLocation and my data is accurate. I also need this for calculating distance between user location and a place so I can immediately return true or false if it is within the range. I find this very useful as I get location within 0.006 seconds and handy and got it from apple documentation only but still I dont know if it is a best practice.
What happens if I call startUpdatingLocation while startMonitoringSignificantLocationChanges is running? Does significantLocationChange monitoring get stopped? If I then stopUpdatingLocation will significantLocationChange monitoring continue or restart?
I can find no documentation covering the interplay between these two ways of monitoring location.
I don't think the accepted answer really answers the question asked. I did some tests and you can use both if you want and they will not cancel each other out.
Why would someone want to use both ? Because startMonitoringSignificantLocationChanges wakes up the app from being suspended or terminated without the need of any background modes. So if you run both you can get accurate foreground location updates and significant location change background location updates.
Of course, you can switch the method, when going into background but a) that wasn't the question b) it adds unneeded logic
Of course, there's a question if running both methods drains more battery, but my bet is that it doesn't.
They are not meant to be used concurrently. It's either or as they both deliver heading and location changes to the same delegate method.
locationManager:didUpdateToLocation:fromLocation
They differ in the frequency and accuracy (and by extension hardware used and power consumption ) of the changes. You as the developer need to decide which is best based on your use case
I have a need to use both approaches at different times. When I switch from one to the other I set a flag that I can reference in my delegate so that I know the type of update.
Standard location service and significant location change service can be used together. Quote from the API Reference:
If both location services are enabled simultaneously, they deliver
events using the same set of delegate methods.
A good reason to use both is that the standard service gives better accuracy, while the significant location change service works even when your app is suspended.