CLLocation 方法 distanceFromLocation 的问题：结果不准确

Question

我正在尝试使用 distanceFromLocation: 方法来计算我手里拿着 iPhone 行走的总距离。到目前为止，我一直在四处寻找以帮助纠正我的混乱、不准确和看似武断的结果。在这些代码 sn-ps 中，theLabel 只是我的应用程序界面中存在的标签对象，distanceMoved 是我试图存储我走过的总距离的变量，而 locMan 是在我的 @ 中声明的位置管理器接口文件。

- (void)viewDidLoad
{
   locMan = [[CLLocationManager alloc] init];
   locMan.delegate = self;
   [locMan startUpdatingLocation];
   isInitial = true;
   distanceMoved = 0.0;
   [super viewDidLoad];
}

-(void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
   distanceMoved += [newLocation distanceFromLocation: oldLocation];
   theLabel.text = [NSString stringWithFormat: @"%f meters", distanceMoved];
}

对于解决我在这里做错的任何帮助将不胜感激。谢谢！

Answer 1

1. 过滤掉缓存的（旧的）位置数据，
2. 过滤掉无效的定位结果（精度
3. 将精度要求设置为kCLLocationAccuracyBest，
4. 设置最小距离过滤器，最好至少 10 米以过滤掉位置噪声。
5. 编辑：当oldLocation 为零时，不要计算距离。

您还可以做更多的事情，但只要您获得足够好的水平精度（

添加一个 NSLog（见下文），以便您了解发生了什么。如果您仍然没有得到好的结果，请发布 NSLog 的输出，以便我们查看发生了什么并提供更多帮助。

-(void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    NSTimeInterval age = -[newLocation.timestamp timeIntervalSinceNow]; 

    if (age > 120) return;    // ignore old (cached) updates

    if (newLocation.horizontalAccuracy < 0) return;   // ignore invalid udpates

    // EDIT: need a valid oldLocation to be able to compute distance
    if (oldLocation == nil || oldLocation.horizontalAccuracy < 0) return; 

    CLLocationDistance distance = [newLocation distanceFromLocation: oldLocation];

    NSLog(@"%6.6f/%6.6f to %6.6f/%6.6f for %2.0fm, accuracy +/-%2.0fm",
        oldLocation.coordinate.latitude,
        oldLocation.coordinate.longitude,
        newLocation.coordinate.latitude,
        newLocation.coordinate.longitude, 
        distance,
        newLocation.horizontalAccuracy);

    distanceMoved += distance;
    theLabel.text = [NSString stringWithFormat: @"%f meters", distanceMoved];
}

- (void)viewDidLoad
{
   locMan = [[CLLocationManager alloc] init];
   locMan.delegate = self;
   locMan.desiredAccuracy = kCLLocationAccuracyBest;
   locMan.distanceFilter = 10;

   [locMan startUpdatingLocation];
   isInitial = true;
   distanceMoved = 0.0;
   [super viewDidLoad];
}

EDIT for iOS6 如果您想使用didUpdateLocations: 执行相同操作（因为现在不推荐使用上述方法），最简单的解决方案是将每个位置保存在一个属性中，以便在下一个更新你有以前的位置。在类中声明一个属性来保存oldLocation：

@property (nonatomic, retain) CLLocation* oldLocation;

然后在委托方法中保存每个newLocation 以用作下次调用委托方法时的oldLocation：

-(void)locationManager:(CLLocationManager *)manager didUpdateToLocations:(NSArray *)locations
{
    CLLocation* newLocation = [locations lastObject];

    NSTimeInterval age = -[newLocation.timestamp timeIntervalSinceNow]; 

    if (age > 120) return;    // ignore old (cached) updates

    if (newLocation.horizontalAccuracy < 0) return;   // ignore invalid udpates

    // EDIT: need a valid oldLocation to be able to compute distance
    if (self.oldLocation == nil || self.oldLocation.horizontalAccuracy < 0) {
        self.oldLocation = newLocation;
        return; 
    }

    CLLocationDistance distance = [newLocation distanceFromLocation: self.oldLocation];

    NSLog(@"%6.6f/%6.6f to %6.6f/%6.6f for %2.0fm, accuracy +/-%2.0fm",
        self.oldLocation.coordinate.latitude,
        self.oldLocation.coordinate.longitude,
        newLocation.coordinate.latitude,
        newLocation.coordinate.longitude, 
        distance,
        newLocation.horizontalAccuracy);

    distanceMoved += distance;
    theLabel.text = [NSString stringWithFormat: @"%f meters", distanceMoved];

    self.oldLocation = newLocation;    // save newLocation for next time
}

Answer 2

您没有设置位置管理器的准确性。浏览苹果文档，它类似于accuracy = bestfornavigation。或者其他的东西。这应该会像地狱一样耗尽电池，但就是为了这种目的。

编辑：只记得我手头有它。

// Create the Location Manager
locationManager = [[CLLocationManager alloc] init];

// Configure the Location Manager
locationManager.delegate = self;
locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;

Answer 3

CLLocationDistance distance = [secondLocation distanceFromLocation:firstLocation];  // distance is expressed in meters

CLLocationDistance kilometers = distance / 1000.0;
// or you can also use this..
CLLocationDistance meters = distance;

NSString *distanceString = [[NSString alloc] initWithFormat: @"%f", kilometers];

flot totaldistancecovered = [distanceString floatValue];

//Now,you can use this float value for addition...
// distanceMoved  should be float type variable which is declare in .h file...

 distanceMoved = distanceMoved + totaldistancecovered ;
 theLabel.text = [NSString stringWithFormat: @"%f meters", distanceMoved];

希望这会对你有所帮助..

Answer 4

您应该做的第一件事是通过检查您从位置管理器收到的第一个更新的时间戳来释放第一个更新，它通常会缓存最后一个已知位置。其次要记住准确性，你得到的初始值总是在一个很大的范围内。