iphone - CLLocation 方法 distanceFromLocation : Inaccurate results 出现问题

Question

我正在尝试使用 distanceFromLocation: 方法来计算我手持 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令人困惑、不准确且看似武断的结果。在这些代码片段中，theLabel 只是一个出现在我的应用程序界面中的标签对象，distanceMoved 是我试图存储我走过的总距离的变量，而 locMan 是一个在我的@interface 文件中声明的位置管理器.

- (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];
}

如果您能帮助解决我在这里做错的问题，我们将不胜感激。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(准确度 < 0)，
3. 将精度要求集设置为 kCLLocationAccuracyBest,
4. 设置一个最小距离过滤器，最好至少为 10 米，以滤除位置噪音。
5. 编辑:当oldLocation 为零时不计算距离。

您还可以做更多事情，但只要您获得足够好的 horizo​​nalAccuracy (<30m)，这应该可行。您可以过滤掉低准确度的结果，但您必须自己跟踪 oldLocation，这有点复杂。

添加一个 NSLog(见下文)以便您可以了解发生了什么。如果您仍然没有得到好的结果，请发布 NSLog 的输出，以便我们了解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];
}

编辑 iOS6 如果您想使用 didUpdateLocations: 做同样的事情(因为现在不推荐使用上述方法)最简单的解决方案是简单地将每个位置保存在属性中，以便在下一次更新时您拥有以前的位置。在类中声明一个属性来保存 oldLocation:

@property (nonatomic, retain) CLLocation* oldLocation;

然后在委托(delegate)方法中保存每个 newLocation 以用作下次调用委托(delegate)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
}