Core Location is a framework in the iOS SDK that provides device location. There are three technologies that can be used to obtain locations: GPS, cellular or WiFi. Among these technologies, GPS is the most accurate, and if there is GPS hardware, Core Location will use it first. If the device does not have GPS hardware (such as a WiFi iPad) or fails to get the current location using GPS, Core Location will fall behind and choose to use cellular or WiFi.
Most of the features of Core Location are provided by the CLLocationManager, which can use the location manager to specify the frequency and accuracy of location updates, as well as to start and stop receiving these updates.
To use the Location Manager, you must first add the framework Core Location to the project and then import its interface file:
#import <CoreLocation/>
and initialize the location manager, specify the update agent, and some update settings, and then update
CLLocationManager *locManager = [[CLLocationManager alloc] init]; = self; [locManager startUpdatingLocation];
There are two location-related methods for the location manager delegate:
- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
CLLocation *curLocation = [locations lastObject];
if( > 0)
{
NSLog(@"Current position: %.0f, %.0f +/- %.0f meters",,
,
);
}
if( > 0)
{
NSLog(@"Current altitude: %.0f +/- %.0f meters",,);
}
}
- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{ //This method is called when the location fails. And since it will be repositioned after failure, updates must be stopped at the end
if( == kCLErrorLocationUnknown)
{
NSLog(@"Currently unable to retrieve location.");
}
else if( == kCLErrorNetwork)
{
NSLog(@"Network used to retrieve location is unavailable.");
}
else if( == kCLErrorDenied)
{
NSLog(@"Permission to retrieve location is denied.");
[manager stopUpdatingLocation];
}
}
The first method handles positioning successfully, and the manager parameter represents the location manager instance; locations are an array, which is a collection of location changes, and it is stored in the order of time changes. If you want to get the current location of the device, you only need to access the last element of the array. Each object type in the collection is CLLocation, which contains the following properties:
coordinate — coordinate — coordinate. A structure encapsulating longitude and latitude.
altitude — altitude. Positive numbers are above sea level, while negative numbers are below sea level.
horizontalAccuracy — The accuracy of the position (radius). Position accuracy is represented by a circle, and the actual position may be anywhere within the circle. This circle is determined by coordinate and horizontalAccuracy. The larger the value of horizontalAccuracy, the larger the defined circle, and therefore the lower the position accuracy. If the value of horizontalAccuracy is negative, it means that the value of coordinate is invalid.
verticalAccuracy — Accuracy of altitude. The error indicating the altitude is the corresponding number of meters when a positive value is the positive value; the value indicating the altitude is invalid if it is negative.
speed — speed. This property is calculated by comparing the current position and the previous position and comparing the time difference and distance between them. Given the frequency of Core Location updates, the value of the speed attribute is not very accurate unless the movement speed changes very little.
When the application starts tracking the user's location, a prompt box will be displayed on the screen whether to allow positioning. If the user disables the location service, iOS does not prohibit the application from running, but the location manager will generate an error.
The second method handles this positioning failure, and the parameters of this method indicate the cause of the failure. If the user prohibits application positioning, the error parameter will be kCLErrorDenied; if the Core Location cannot confirm the location after efforts, the error parameter will be kCLErrorLocationUnknown; if there is no source for obtaining the location, the error parameter will be kCLErrorNetwork.
Usually, Core Location will continue to try to determine the location after an error occurs, but it won't do so if the user disables the location; in this case, the method stopUpdatingLocation should be used to stop the location manager.
Position accuracy can be specified according to actual conditions. For example, for applications that simply determine which country the user is in, it is not necessary to require the Core Location to be 10 meters accurate. To specify accuracy, set the desiredAccuracy of the Location Manager before starting the location update. There are 6 enum values representing different precisions:
extern const CLLocationAccuracy kCLLocationAccuracyBestForNavigation; extern const CLLocationAccuracy kCLLocationAccuracyBest; extern const CLLocationAccuracy kCLLocationAccuracyNearestTenMeters; extern const CLLocationAccuracy kCLLocationAccuracyHundredMeters; extern const CLLocationAccuracy kCLLocationAccuracyKilometer; extern const CLLocationAccuracy kCLLocationAccuracyThreeKilometers;
After starting an update to Location Manager, the update will be passed to Location Manager delegate until the update stops. You cannot directly control the frequency of these updates, but you can use the location manager's property distanceFilter for indirect control. Set the property distanceFilter before starting the update, which specifies how many meters the device (horizontal or vertical) moves before sending another update to the delegate. The following code starts the Location Manager using settings suitable for tracking trekkers:
CLLocationManager *locManager = [[CLLocationManager alloc] init]; = self; = kCLLocationAccuracyHundredMeters;//The positioning accuracy is within 100 meters = 200;//Move horizontally or vertically for 200 meters to call the agent to update the position [locManager startUpdatingLocation];//Start location update
. The higher the accuracy required for positioning and the smaller the value of the attribute distanceFilter, the greater the power consumption of the application.
The location manager has a headingAvailable property that indicates whether the device is equipped with a magnetic compass. If this property is YES, you can use Core Location to obtain heading information. The receiving heading update is very similar to the receiving position update. To start receiving heading updates, you can specify the location manager delegation, set the attribute headingFilter to specify what frequency to receive updates (measured by the degree of heading change) and call the method startUpdatingHeading to the location manager:
The Location Manager Delegation Agreement defines the method used to receive heading updates. The protocol has two heading-related methods:
- (BOOL)locationManagerShouldDisplayHeadingCalibration:(CLLocationManager *)manager
{
return YES;
}
- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
}
The first method specifies whether the location manager displays calibration prompts to the user. This prompt will automatically rotate the device 360°. Since the compass always self-calibrates, this tip is only helpful if the compass reads fluctuate violently. When set to YES, the prompt may distract the user or affect the user's current operations.
The parameter newHeading of the second method is a CLHeading object. CLHeading provides heading readings through a set of properties: magneticHeading and trueHeading. The unit of these values is degrees and is of type CLLocationDirection, which is a double-precision floating point number. This means:
If the heading is 0.0, the direction of progress is north;
If the heading is 90.0, the direction of progress is east;
If the heading is 180.0, the direction of progress is south;
If the heading is 270.0, the direction of travel is west.
The CLHeading object also contains attributes headingAccuracy, timestamp (measurement time of reading), and description (this description is more suitable for writing to logs rather than displaying to the user). The following demonstrates using this method to handle heading updates:
- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
if( >=0)
{
NSString *headingDesc = [NSString stringWithFormat:@"%.0f degrees (true), %.0f degrees (magnetic)",,];
NSLog(@"%@",headingDesc);
}
}
trueHeading and magneticHeading represent the true heading and magnetic heading respectively. If the location service is turned off, GPS and wifi can only obtain magneticHeading (magnetic field heading). Only by opening the location service can trueHeading be obtained.
The following code demonstrates the distance and correct heading of the current location when there is a location that determines the latitude and longitude:
#import ""
#define kDestLongitude 113.12 //Absolution#define kDestLatitude 22.23 //latitude#define kRad2Deg 57.2957795 // 180/π
#define kDeg2Rad 0.0174532925 // π/180
@interface ViewController ()
@property (strong, nonatomic) IBOutlet UILabel *lblMessage;
@property (strong, nonatomic) IBOutlet UIImageView *imgView;
@property (strong, nonatomic) CLLocationManager *locationManager;
@property (strong, nonatomic) CLLocation *recentLocation;
-(double)headingToLocation:(CLLocationCoordinate2D)desired current:(CLLocationCoordinate2D)current;
@end
@implementation ViewController
- (void)viewDidLoad
{
[super viewDidLoad];
= [[CLLocationManager alloc] init];
= self;
= kCLLocationAccuracyThreeKilometers;
= 1609; //1 mile ≈1609 meters [ startUpdatingLocation];
if([CLLocationManager headingAvailable])
{
= 10; //10°
[ startUpdatingHeading];
}
}
/*
* According to Movable Type Scripts
* /library/drmath/view/
*
* Javascript:
*
* var y = (dLon) * (lat2);
* var x = (lat1)*(lat2) -
* (lat1)*(lat2)*(dLon);
* var brng = Math.atan2(y, x).toDeg();
*/
-(double)headingToLocation:(CLLocationCoordinate2D)desired current:(CLLocationCoordinate2D)current
{
double lat1 = *kDeg2Rad;
double lat2 = *kDeg2Rad;
double lon1 = ;
double lon2 = ;
double dlon = (lon2-lon1)*kDeg2Rad;
double y = sin(dlon)*cos(lat2);
double x = cos(lat1)*sin(lat2) - sin(lat1)*cos(lat2)*cos(dlon);
double heading=atan2(y,x);
heading=heading*kRad2Deg;
heading=heading+360.0;
heading=fmod(heading,360.0);
return heading;
}
//Training- (void)locationManager:(CLLocationManager *)manager didUpdateHeading:(CLHeading *)newHeading
{
if(!=nil && >=0)
{
CLLocation *destLocation = [[CLLocation alloc] initWithLatitude:kDestLatitude longitude:kDestLongitude];
double course = [self headingToLocation: current:];
double delta = - course;
if (abs(delta) <= 10)
{
= [UIImage imageNamed:@"up_arrow.png"];
}
else
{
if (delta > 180)
{
= [UIImage imageNamed:@"right_arrow.png"];
}
else if (delta > 0)
{
= [UIImage imageNamed:@"left_arrow.png"];
}
else if (delta > -180)
{
= [UIImage imageNamed:@"right_arrow.png"];
}
else
{
= [UIImage imageNamed:@"left_arrow.png"];
}
}
= NO;
}
else
{
= YES;
}
}
//The processing of positioning is successful- (void)locationManager:(CLLocationManager *)manager didUpdateLocations:(NSArray *)locations
{
CLLocation *curLocation = [locations lastObject];
if( >= 0)
{
= curLocation;
CLLocation *destLocation = [[CLLocation alloc] initWithLatitude:kDestLatitude longitude:kDestLongitude];
CLLocationDistance distance = [destLocation distanceFromLocation:curLocation];
if(distance<500)
{
[ stopUpdatingLocation];
[ stopUpdatingHeading];
= @"You have arrived at your destination!";
}
else
{
= [NSString stringWithFormat:@"It's still %f meters away from the destination",distance];
}
}
}
//Processing positioning failed- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error
{
if( == kCLErrorLocationUnknown)
{
NSLog(@"Currently unable to retrieve location.");
}
else if( == kCLErrorNetwork)
{
NSLog(@"Network used to retrieve location is unavailable.");
}
else if( == kCLErrorDenied)
{
NSLog(@"Permission to retrieve location is denied.");
[ stopUpdatingLocation];
= nil;
}
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end
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