iOS Core Location 实现定位

在iphone中可以用core location功能来实现地理定位，并可用mapkit 框架加载google地图。
想得到定点的信息，其实 不难，只需要涉及到几个类，CLLocationManager, CLLocation, CLLocationManagerdelegate协 议，CLLocationCoodinate2D, CLLocationDegrees。
<一>先实例化一个CLLocationManager,同时设置委托及精确度等。
CCLocationManager *manager = [[CLLocationManager alloc] init];
[manager setDelegate: self];
[manager setDesiredAccuracy: kCLLocationAccuracyBest];
其中desiredAccuracy属性表示精确度，有利5种选择如下:
       desiredAccuracy属性
              描述
kCLLocationAccuracyBest
精确度最佳
kCLLocationAccuracynearestTenMeters
精确度10m以内
kCLLocationAccuracyHundredMeters
精确度100m以内
kCLLocationAccuracyKilometer
精确度1000m以内
kCLLocationAccuracyThreeKilometers
精确度3000m以内
NOTE:精确度越高，用点越多，就要根据实际情况而定。
manager.distanceFilter = 250;这个表示在地图上每隔250m才更新一次定位信息。
[manager startUpdateLocation]; 启动定位器，如果不用的时候就必须调用stopUpdateLocation以关闭定位功能。
<二>CCLocation对像中包含着定点的相关信息数据。其属性主要包括coordinate, altitude,horizontalAccuracy,verticalAccuracy, timestamp等，分别如下：
coordinate 用来存储地理位置的latitude和longitude,分别表示 纬度和经度，都是float类型.如可这 样： float latitude = location.coordinat.latitude; location是CCLocation的实例。 这里也把上面提到的CLLocationDegrees，它其实是一个double类型，在core Location框架中是用来储存 CLLocationCoordinate2D实例coordinate的latitude 和longitude，
typedef double CLLocationDegrees;
typedef struct 
  {CLLocationDegrees latitude; 
  CLLocationDegrees longitude}  CLLocationCoordinate2D;
altitude 表示位置的海拔高度，这个值是极不准确的。
horizontalAccuracy 表示水平准确度，这么理解，它是以coordinate为圆心的半径，返回的值越小，证明准确度越好，如果是负数，则表示core location定位失败。
verticalAccuracy表示垂直准确度，它的返回值与altitude相关，所以不准确。
Timestamp 返回的是定位时的时间，是NSDate类型。
<三>CLLocationMangerDelegate协议
    我们只需实现两个方法就可以了，如下:
- (void)locationManager:(CLLocationManager *)manager 
didUpdateToLocation:(CLLocation *)newLocation 
   fromLocation:(CLLocation *)oldLocation ;
- (void)locationManager:(CLLocationManager *)manager 
   didFailWithError:(NSError *)error;
上面第一个是定位时候回访调，后者定位出错时被调。
<四>现在可以去实现定位了：
新建一个view-based application模板的工程，假设项目名称为coreLocation.我们在contronller的头文件和源文件中的代码大概有如下：
.h
#import <UIKit/UIKit.h>
#import <CoreLocation/CoreLocation.h>
@interface CoreLocationViewController : UIViewController 
<CLLocationManagerDelegate>{
 CLLocationManager *locManager;
}
@property (nonatomic, retain) CLLocationManager *locManager;
@end
.m
#import "CoreLocationViewController.h"
@implementation CoreLocationViewController
@synthesize locManager;
// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.
- (void)viewDidLoad {
locManager = [[CLLocationManager alloc] init];
locManager.delegate = self;
locManager.desiredAccuracy = kCLLocationAccuracyBest;
[locManager startUpdatingLocation];
    [super viewDidLoad];
}
- (void)didReceiveMemoryWarning {
// Releases the view if it doesn't have a superview.
    [super didReceiveMemoryWarning];
// Release any cached data, images, etc that aren't in use.
}
- (void)viewDidUnload {
// Release any retained subviews of the main view.
// e.g. self.myOutlet = nil;
}
- (void)dealloc {
[locManager stopUpdatingLocation];
[locManager release];
[textView release];
    [super dealloc];
}
#pragma mark -
#pragma mark CoreLocation Delegate Methods
- (void)locationManager:(CLLocationManager *)manager 
didUpdateToLocation:(CLLocation *)newLocation 
   fromLocation:(CLLocation *)oldLocation {
CLLocationCoordinate2D locat = [newLocation coordinate];
float lattitude = locat.latitude;
float longitude = locat.longitude;
float horizon = newLocation.horizontalAccuracy;
float vertical = newLocation.verticalAccuracy;
NSString *strShow = [[NSString alloc] initWithFormat:
@"currentpos: 经度＝%f 维度＝%f 水平准确读＝%f 垂直准确度＝%f ", 
lattitude, longitude, horizon, vertical];
UIAlertView *show = [[UIAlertView alloc] initWithTitle:@"coreLoacation" 
           message:strShow delegate:nil cancelButtonTitle:@"i got it"
           otherButtonTitles:nil];
[show show];
[show release];
}
- (void)locationManager:(CLLocationManager *)manager 
   didFailWithError:(NSError *)error{
NSString *errorMessage;
if ([error code] == kCLErrorDenied){
                errorMessage = @"你的访问被拒绝";}
if ([error code] == kCLErrorLocationUnknown) {
               errorMessage = @"无法定位到你的位置!";}
UIAlertView *alert = [[UIAlertView alloc]
        initWithTitle:nil  message:errorMessage 
      delegate:self  cancelButtonTitle:@"确定"  otherButtonTitles:nil];
[alert show];
[alert release];
}
@end