Im developing a location based application for a football stadium.
I must pre define several locations on the map for the user and guide the user to that location.
Do anyone know what is the error margin in CLLocationManager current use location
It depends on the Accuracy Constant you set. From the docs:
kCLLocationAccuracyBestForNavigation
Use the highest possible accuracy and combine it with additional
sensor data. This level of accuracy is intended for use in navigation
applications that require precise position information at all times
and are intended to be used only while the device is plugged in.
Available in OS X v10.7 and later. Declared in CLLocation.h.
kCLLocationAccuracyBest
Use the highest-level of accuracy. Available in OS X v10.6 and later.
Declared in CLLocation.h.
kCLLocationAccuracyNearestTenMeters
Accurate to within ten meters of the desired target. Available in OS X
v10.6 and later. Declared in CLLocation.h.
kCLLocationAccuracyHundredMeters
Accurate to within one hundred meters. Available in OS X v10.6 and
later. Declared in CLLocation.h.
kCLLocationAccuracyKilometer
Accurate to the nearest kilometer. Available in OS X v10.6 and later.
Declared in CLLocation.h.
kCLLocationAccuracyThreeKilometers
Accurate to the nearest three kilometers. Available in OS X v10.6 and
later. Declared in CLLocation.h.
UPDATE:
Here is a bit more information about its accuracity
if you use kCLLOcationAccuracyBest and you have a good view to open sky, you will get 3-6m positional accuracy in 95% of measures. if you have bad view, up to 30m can happen.
This is the best what you can achieve. The iphone has one of the best GPS modules (if not the best at all in consumer devices). But best is to try it out. I am not sure if the GPS receives good signals through the partial roof of the stadium. the bigger the stadium the better the view to sky which gives better accuracy.
Use a GPS App which supports waypoints, and set some waypoints.
Do the same 1 hour later, and compare the distance error. (or try to view in google maps)
Related
How to specify the entire country as a region in region identifier.Wether it will accept the
identifier as :#"Uk"
here the code to reo identifier.How can i specify England or UK.Please help me to sort out
CLLocationCoordinate2D location2D = mapView.region.center;
CLRegion *regionForMonitoring = [[CLRegion alloc] initCircularRegionWithCenter:location2D radius:1 identifier:#"RegionIdentifier"];
[[Utils getLocationManager] startMonitoringForRegion:regionForMonitoring];
CLRegions are totally unsuitable for this purpose.
First of all, the radius specified is the distance in meters that the region covers - so in your case you are asking the system to monitor a region at a specific lat/long with a radius of 1 meter!
Also, system regions have a maximum number of regions that can be monitored (around 10 or so), and a maximum radius that can be used of around 400 meters after which the region will not work.
You really need to read the "Monitoring Shape Based Regions" section of this Apple document:
http://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/LocationAwarenessPG/CoreLocation/CoreLocation.html
There are two other possible approaches to what you are trying to do:
1) Use Significant Location Updates, and test on each update if you are in an area with a shape you specify.
2) Use CoreTelephony to look up the cell carrier your device is on and see if the carrier number matches one in the country of interest. Of course, this will not work on some iPads or other iOS devices with no cell connection.
Neither of those approaches will be exact around the edges, but will also not consume nearly as much battery life as using the GPS.
i am developing an app which is particularly dependent upon the distance between two iOS devices. I am using GPS location of devices to calculate the distance between them.
To calculate distance, i am using cllocation -distanceFromLocation method but the values generated by method is fluctuating and differs from actual distance between devices and cannot be considered even as an approximate result.
For example, if the actual distance between devices is 2 to 3 meters, it gives me the result around 14 meters at some point and 43 meters at another point. Is the the function -distanceFromLocation: is not so precise and accurate????
Is there any better alternative for calculating distance using GPS latitude and longitude of devices???
Please help me out.
Thanx in advance.
The accuracy of CoreLocation GPS varies greatly depending on your surroundings.
At it's most accurate it can go down to a couple of metres resolution (I'm not sure exactly) but if you're indoors it will be more like 20-50 metres.
I'm guessing that you're developing and testing the app indoors and so the fluctuations would be about normal.
Even outdoors in perfect weather CoreLocation will struggle to accurately tell you the distance between two devices over a short distance. (i.e. a couple metres).
For short range you might be better using wifi signal strength instead. Although this can also change from room to room.
Essentially, it's difficult to accurately detect the distance between two devices.
Sorry for being a noob here. I am not able to clearly differentiate between CLLocationManager's properties distanceFilter and desiredAccuracy.
If I want my application to give different coordinates for even small distances (say 100-200 metres) what values should i set for these properties.
Help would be greatly appreciated.
According to developer.apple.com
distanceFilter
The minimum distance (measured in meters) a device must move laterally
before an update event is generated.
That means, based on previous location event, another location update will only be received after exceeding distanceFilter value distance.
desiredAccuracy refers to how accurate your location data should be.
For example if you wish to see the exact street you're on you a high accuracy value for this parameter. (kCLLocationAccuracyBest)
If you only wish to see the approximate area (such as in which neighbourhood you're in) you'd set a lower accuracy value for this param. (kCLLocationAccuracyThreeKilometers)
Choose this to suit your needs, however be aware that the more precise you wish to be and the more often you request updates, the more power it will drain from your device.
Hope this helps,
Vlad
distanceFilter - this is minimal distance which device should pass from previous location which was passed to delegate with ...didUpdateToLocation:... method. And as soon as distance reached location service will invoke ...didUpdateToLocation... again and so on.
desiredAccuracy - tells to location service how accurate coordinate you want and this is minimal location error radius. If value is very low (ex. 5) radio will try to use GPS hardware and will keep powering it up hardly to make it give most accurate location. If value is large,than system may decide to use data which was retrieved from WiFi hotspots location triangulation.
Using iPhone's SDK GPS API, how accurate can I get? Is it within a few meters or kilometers? I'm interested in the accuracy when it is indoor. My software will only be used in door.
The best possible accuracy seems to be 9 meters. Common values (outdoor, good coverage) is 17 m, 23 m and 49 meters. With trees covering the sky you'll probably stay under a hundred meters, but hardly accurate enough for GIS or anything like that.
The API has a property or method that returns the current accuracy of the location measurement. If your goal is only to use the location if accuracy is within some limit then you should make sure that you check the returned accuracy, since the location may be only accurate to within a few thousand meters initially as its just using your location from the cell towers, and it will typically get better and better accuracy as the GPS powers up and starts getting a fix.
Most standard GPS chips (and the iphone is that) can get around 10 meters accuracy.
Best results are outside on a clear sky obviously.
The difference between GPS chips is usually how quickly they can reception and how well they can hold it. Accuracy is pretty constant except for those using WAAS sattelite (which the iphone GPS doesn't do)
Based on my own experience it's within meters.
I'd like to use reliable locations, even on an old iphone. However, many readings (particularly from cell towers) are too inaccurate. I think.
When I plot my position + accuracy radius (or look at google maps app), I notice the center of the estimated circle is generally close to my physical location. I'm guessing that if I cut the "accuracy" number in half, I'll still be in the circle 99% of the time.
I believe this is a probabilistic game - the location manager is trying to provide an estimate that's correct 99.99999% of the time, so they give a deliberately wide margin. Any thoughts/info?
The CoreLocation framework gives you the radius of the circle for every CLLocation you get using the horizontalAccuracy/verticalAccuracy properties. You can specify to the CLLocationManager a desiredAccuracy property that use these types:
kCLLocationAccuracyNearestTenMeters, kCLLocationAccuracyHundredMeters, kCLLocationAccuracyKilometer, kCLLocationAccuracyThreeKilometers;
So you get notifications when you get inside your desired range. That said, when you use the CLLocationManager the first event is given to you ASAP, and then the proceeding events are the ones that satisfy your conditions.
When you're using CoreLocation, you're getting back "answers" that get better and better. I've noticed that the "best" answer is almost always accurate to within 100m, so theoretically you could probably cut down on the "buffer" that you're normally given. The only way to really know, though, and this is what I would do, is to test test test. Find iphones and ipods from all generations and see what types of accuracies you're getting and what types of results you're getting. In a lot of ways, it depends on the type of app you're making, but if you want to deliver sensitive or important information based on where the user is, you should really wait for the framework to give you a nearly exact location.