This is stated in CLLocationManager class reference:
When requesting high-accuracy location data, the initial event delivered by the location service may not have the accuracy you requested.
This is really affecting my app. How can I make sure that the location found is the one with the correct accuracy?
I tried to use the 4th or 5th update rather than first retrieved location but this is not a good solution. Any idea?
You should check the accuracy of the updates, CLLocation
contains a property horizontalAccuracy which you can use to check the accuracy.
When the CLLocation has an accuracy that you find accurate enough you use and ignore al others.
Als you should tel CLLocationManager your desired accuracy. To do this set the desiredAccuracy property in CLLocationManager.
I think you will have to live with that. That's how Apple implemented it. Getting a fine grained position takes time, just think about how long any windshield-mounted GPS devices in cars take to fix up their position.
So instead of letting your application wait for a longer time, they provide with what accuracy is available almost immediately, based on cell-towers and WiFi hotspots in the vicinity. Only when there has been a more reliable GPS fix will they call into your app again and let you know.
In the end, it is just a question of where the waiting for the fine-grained position is: In your app, where you have the chance of doing something with the more coarse-grained data you get quickly, or in their framework with no chance for apps to do anything useful in the meantime. I think, letting you decide is the better choice.
Depending on the type of app, you could have a map that automatically zooms in deeper as soon as better position data comes in, draw a smaller circle around the position you are expecting etc. For the end user, nothing's worse than waiting without getting any feedback. So even though this is probably not the answer you would have liked, I advise to make the best of it from a user's perspective.
Related
I am working on a feature in an iOS app to send location updates to our backend when there is a change in the location.
Initially, I had set minimalDistanceFilter(minimum change in location value) to none to send location updates. But it is making the network calls continuously and it can increase the load on the backend.
If some of you worked on this case earlier, I wanted to know how you solved it. What can be the minimalDistanceFilter?
I am also curious about how the above-listed apps work with location-related events.
The distanceFilter and the desiredAccuracy go hand-in-hand. For the distance filter, it can be anything between kCLDistanceFilterNone and CLLocationDistanceMax. See the documentation.
Regarding what other people used, it will vary widely from app to app. For navigation apps, you tend to need high accuracy so you don't miss a turn. But a weather app might be perfectly happy with city-level accuracy.
If you really need reasonable precision and want to reduce volume, then a filter of 5–15 meters is a good starting point. Try different values yourself and see what the effect is.
But there is no magical answer to your question. You will have to balance the legitimate needs of your app with (a) the server load; and (b) the power consumption on the device.
By the way, if the app doesn't need high accuracy, you might contemplate the very efficient, but less accurate, significant change service which will report changes of roughly 500 meters, with a frequency not exceeding once every 5 minutes
Finally, remember, nowadays the user is in control of the accuracy. You can request whatever accuracy you want, but if the user wants to preserve their privacy, they can choose not to share their precise location, and there is nothing you can do about it (other than to try to make a case for why precise location data is essential for the proper functioning of your app).
I want to Know what does startmonitoringsignificantlocationchanges uses to deliver location, is it GPS or Wifi/Internet? My Understanding is it uses cellular or wifi,to know if device has moved significantly but what I don't know is, at time of picking location does it use GPS alone to pick up location.
My Findings are : I travelled 30 KM in City Train but did not get any locations in background and during this journey my Wifi and Cellular data was off. So please tell if Significant fails to provide locations based on GPS only.
Building location apps in the past, I assumed that GPS was only used when startUpdatingLocation() was called. After double-checking the docs, Apple doesn't explicitly state whether significantLocationChanges CAN use GPS, but it is a power-saving option, and their docs specify that it "requires the presence of cellular hardware", which makes me pretty certain that my assumption (and yours) are correct. I'd leave this up for a bit, in case there's a hardware expert who knows for sure. The docs you want: https://developer.apple.com/reference/corelocation/cllocationmanager
Like all location functionality, it uses a combination of cell, wifi, and GPS. Use of cell is primary. The idea is to keep use of GPS to a minimum, in order to prevent drain on the battery.
You certainly cannot expect this to work with the cell turned off; indeed, if your code properly checks significantLocationChangeMonitoringAvailable with the cell off, I would intuitively expect the answer to be false.
(Also note that you will not get any events unless you have a location manager with a delegate.)
As explained in this answer "Hows does Significant Location Change work?" (and in WWDC videos from 2013-2015) Significant location change monitoring uses a technique called Cell Tower Triangulation.
You can think of it as almost the same mechanism as GPS triangulation except that the cellular hardware will be used to gauge distance from nearby cell towers instead of firing the GPS hardware to get signals from actual satellites.
In my experience I've noticed that this method gives accuracy of approx. 1000m. It does not use the GPS hardware and hence is more battery efficient. It is good for coarse location updates. See WWDC 2013 session Harnessing iOS to Create Magic in Your Apps where the presenter makes a passing reference to this technology.
What's the best way to determine whether the user is at a specific location, i.e. at a gas station?
I've implemented an approach where the app is listening for major location changes until the user get's close enough to a location. Then the app switches to the more accurate location updates (kCLLocationAccuracyBest). It then checks if the user is close enough, and if so, I consider this as a "check-in". This works quite well. If the user moves away from our location of interest, I switch back to the major location updates to save energy.
This works as the user does not live or work within the first threshold (I currently use 300 meters). This situation drains the user's battery for no reason. If I set this threshold to low, the major location updates might not be accurate enough to detect the user in front of our location.
I'm using MKLocalSearchRequest to find all the places of interest in close proximity to the user.
So, I assume there are better ways. Any suggestions?
Thanks!
– Flo
iBeacons are the low power way if that fits your use case. http://en.m.wikipedia.org/wiki/IBeacon Is a suprisingly good overview
They are reasonably cheap, and can be simulated with computer software
I would like my iOS app to get notified in background whenever user stops (or slows down below some velocity threshold) at a place while maintaining maximum battery life.
The catch is that I don't really care for accuracy when the user is moving but I need as accurate measurement as possible when user stops or walks around the same spot.
There are many Core Location tools available:
Standard Location Service
Significant Change Location Service
Geofencing and Ranging Service
Integration with Core Motion and M7 Motion Coprocessor
Which one of them should I use? Is there a best practice for what I am attempting to do? Has anybody experience with this sort of stuff? I found this app which does exactly what I want to incorporate in my app but I'm not permitted to use their API.
I've read the documentation but my case doesn't really fit any of the categories they discuss.
Thanks in advance.
Pete.
In iOS8 there is a new technology that fits what it sounds like you are asking for. CLVisit objects are sent to your app in the background when the user arrives or departs after stopping at a location. Power consumption is very low with this feature. You enable it by calling startMonitoringVisits on a CLLocationManager object.
I'm currently searching a way for device using firefox OS to communicate with device's gps, so it can get the exact location positioning, rather than the w3c geolocation api which is not as accurate as gps realtime.. Thanks!
Simple answer: it isn't possible to access the "device's GPS" directly. You only have the Geolocation API that you already know.
Long answer: My experience with it is not bad at all. So, I think only of two possibilities for not getting "exact location positioning", as you name it:
maybe you're not using the right options to get a precise position. In this case, you could tweak your options a bit to get better results;
maybe you're not waiting until the underlying software can use your GPS instead of some less accurate instrument/estimation (like Wi-Fi positioning estimation).
It can be a combination of both =P
In the first case, you can verify if you're using enableHighAccuracy, like this:
navigator.geolocation.watchPosition(
successCallback,
errorCallback,
{ enableHighAccuracy: true }
);
This will ask the browser for better results, as the standard indicates. Watch out that this may use more battery, and this may not be available anyway. This may take more time too, which is related to my other observation.
In the second case, you may be using a value for timeout that is too small, and maybe it's combined with a maximumAge that may be too high.
If maximumAge is high and timeout is small, you get an out dated position, as there won't be enough time to get a new position and you accept an old one.
If both are small, you'll start to get lots of TIMEOUT errors (the value is 3), as there'll be no positions for you.
You need to find the right balance between all 3 options to get the best positions. And you have to be patient sometimes.
Play with all 3 options and take a look at the errors you get. They'll tell you a lot about your issue getting precise and accurate coordinates.
The position object has some attributes that may come in handy to analyze what's happaning:
the position.timestamp attribute will tell you how old that position object is. If this is old, you know you should tweak the options
the position.coords.accuracy attribute will tell you the accuracy level of the lat/long coordinates. If this is too big (it's in meters), you know you should tweak the options
If you wait forever, on a place where the GPS should work well (say, outdoors, on a clean field), and you keep getting inaccurate results, maybe you can't do much better anyway. I'd say it's not possible anyway, with your software+hardware =(
As of now, Firefox OS only has support for GPS positioning (with the latest addition of A-GPS in the mix). That results in the fact, that most of the time you will have to wait from 1 to several minutes at least for the GPS module to acquire lock on your location, and you will need clear look at the sky for the lock to be acquired.
That said, after a lock is acquired, by using the right settings in the call itself (like setting the enableHighAccuracy flag to true) the GPS should provide as accurate position as any other device would.
Right now cell-based and wifi-based geolocation is not available in the current version of the OS (1.0.1 or 1.1.0, either) but is in the pipeline.
You can use the Geolocation API Firefox OS or Google Maps (I do not remember where I got it)