iOS Geofence CLCircularRegion monitoring. location

Question

I am currently trying to get my app to monitor particular regions using CoreLocation however I am finding that it does not seem to work as expected, it seems to me that it cannot work with small a small radius set for each location i.e. 10m.

I've also put together a little test app which plots the circle radius on a map so I can visually see what is happening.

The code I am using for monitoring locations is as follows:

self.locationManager = [[CLLocationManager alloc] init];
self.locationManager.delegate = self;
self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;

// Set-up a region
CLLocationDegrees latitude = 52.64915;
CLLocationDegrees longitude = -1.1506367;
CLLocationCoordinate2D centerCoordinate = CLLocationCoordinate2DMake(latitude, longitude);

CLCircularRegion *region = [[CLCircularRegion alloc] initWithCenter:centerCoordinate
                                                                 radius:10 // Metres
                                                             identifier:@"testLocation"];

[self.locationManager startMonitoringForRegion:region];

I have not put up the code here for DidEnter region etc as I know that works when I go over 100m away from the monitored region.

Here is a screen shot of the app when I am well over 10 meters away from the purple location on the map, the did exit region events do not fire, however if I switch my location to London it fires and also when I set my location back to where the blue location is currently it also fires.

Does anyone know if there is a limitation with the minimum region radius at all or perhaps I am doing something wrong.

Thanks Aaron

Answer 1

I like the answers by both Michael and Nevan. I would like to add more information from my personal experience/opinion in developing Location Based iOS Application with Region Monitoring and also highlight some important points:-

Be realistic on Region Monitoring

Region Monitoring is using Global Positioning System (GPS), Wifi and other technologies to determine if the device is inside or outside the monitored region. Don't forget that our earth is 510 square kilometers and about 30% are land (149 million km2). It is a huge area. Remember the recent MH370 missing case? Our current most advance technology could not even pinpoint an estimated region of that missing plane.

If you want to monitor for a small region with only 10 meter radius. It could possibly work inside a highly dense city with a lot of cell towers and wifi connected areas. But at the same time, the signal might be blocked by high rise towers which might cause the signal loss for a few seconds/minutes which caused the delay in delivering the notification.

So, you really have to consider the above information before deciding how big is the region that you want to monitor. Personally I think 10 meter radius is too small.

Be Realistic on the Number of Monitored Regions

The current Core Location technology can only monitors up to maximum 20 regions on a single app. Make sure that the monitored regions are not too close to each other as well.

I personally have tested 3 regions that are about 100 meters in radius which are about 200 meters aways from each others. Sometimes I can get notifications from all these 3 regions when I am driving through them, but sometimes, I can only get the notification from the First region only. What could be the reason? I could not know. The regions might be too close to each other. Or the cell towers decide that my device does not actually inside the monitored region.

There was one person on StackOverFlow who wants to monitor 1800 points on our Earth. Don't be like him as he is quite unrealistic and probably does not understand the limitation of current Core Location technology. Link: Check if the user location is near of some points

Fine Tune The LocationManager

If your app needs to monitor a small area or needs the location update frequently. Here are the potential properties of your location Manager.

self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
self.locationManager.distanceFilter = kCLDistanceFilterNone;
self.locationManager.activityType = CLActivityTypeAutomotiveNavigation;

kCLLocationAccuracyBestForNavigation will consume more battery compare with kCLLocationAccuracyBest. But, it will be more accurate.

I found a glitch in region monitoring in iOS 7 when there are multiple notifications triggered at the same time in different monitored regions. I have found a solution to filter out this glitch. For more info, please visit: Region Monitoring Glitch on iOS 7 - Multiple Notifications at the same time

Don't Be Over Ambitious

You might have used some apps which can monitor a small region and are very accurate and able to notify your the same second you step into the region. And you have the inspiration to develop the exact same app to compete with them. But do you understand what happens behind scene? What additional technologies that they are using? And what partners that they are collaborating with?

I have done some research on that and found out that some of the technologies that they use are not available publicly. Some of those companies are heavily funded and could pay a premium to the telecommunication companies in order to get the best location accuracy for the best user experience. I do not understand the details on how it works. I believe most of the location determination is actually on the server end (back end), not the mobile (front end).

So, the apps that are developed by those companies not only can pinpoint the best accurate location but also does not consume a lot of battery.

NOTE: I just want to share my 2 cents. The above information consists of my experience and personal opinion. It might not be 100% accurate as I am still learning Core Location and Region Monitoring.

Answer 2

In the past few days iv'e been testing a geofencing feature on my iOS 8.1 device (iPhone 5S) for an app iv'e developed.
The app is registering few regions to the iOS gefence service. The app's logic needs that each geofence radius is between 40 to 80 meters.
I'm seeing so far that in areas with larger number of cell towers and Wifi hot-spots, the geofence detection is good enough on entering regions. That is, in down town areas, business areas etc' the geofence detection is working fine.

Unfortunately, the opposite occurs in areas with few cell towers & wifi networks. My neighborhood, for example, is about 1000 meters width and 500 height (1KM x 0.5KM), and there are no cell towers in it. There are few cell towers thought, on the perimeter that surrounds the neighborhood. Unfortunately In the perimeter of the neighborhood the geofence service detects nothing.

Needless to say that i'm testing with Wifi enabled on the device.

When i test my app on Android: the geofencing service on android 4.3, 4.4 & 5.1 works much better than on iOS. The Android's geofencing service does not detect 100% of region transitions, however it detects 50%-90% of the region transitions.

I conclude the following: If there would have been more cell towers & Wifi hot-spots & if Apple would have improved the geofence service then the detection on iOS devices would have been as good as in Android's.

Answer 3

This is more like an important comment. From Region Monitoring and iBeacon

Testing an iOS App’s Region Monitoring Support

When testing your region monitoring code in iOS Simulator or on a device, realize that region events may not happen immediately after a region boundary is crossed. To prevent spurious notifications, iOS doesn’t deliver region notifications until certain threshold conditions are met. Specifically, the user’s location must cross the region boundary, move away from the boundary by a minimum distance, and remain at that minimum distance for at least 20 seconds before the notifications are reported.

The specific threshold distances are determined by the hardware and the location technologies that are currently available. For example, if Wi-Fi is disabled, region monitoring is significantly less accurate. However, for testing purposes, you can assume that the minimum distance is approximately 200 meters.