使用CLLocationManager计算准确的总步行距离/跑步距离

Question

我试图构建一个iOS应用程序，显示跑步或步行时的总行程。我已经阅读并重新阅读了所有我能找到的文档，但是我无法提供给我一个准确的总距离。

与Nike + GPS或RunKeeper相比，我的应用持续报告更短的距离。他们会首先报告，但随着我不断移动，我的应用与其他正在运行的应用的价值逐渐漂移。例如，如果我步行0.3公里（通过我的车的里程表进行验证），Nike + GPS和RunKeeper都会每次报告〜.3公里，但我的应用程序会报告~13.3公里。 newLocation.horizo​​ntalAccuracy始终为5.0或10.0。

这是我正在使用的代码。我错过了明显的东西吗？关于如何改善这一点以获得更准确的阅读的任何想法？

#define kDistanceCalculationInterval 10 // the interval (seconds) at which we calculate the user's distance 
#define kNumLocationHistoriesToKeep 5 // the number of locations to store in history so that we can look back at them and determine which is most accurate 
#define kValidLocationHistoryDeltaInterval 3 // the maximum valid age in seconds of a location stored in the location history 
#define kMinLocationsNeededToUpdateDistance 3 // the number of locations needed in history before we will even update the current distance 
#define kRequiredHorizontalAccuracy 40.0f // the required accuracy in meters for a location. anything above this number will be discarded 

- (id)init { 
    if ((self = [super init])) { 
     if ([CLLocationManager locationServicesEnabled]) { 
      self.locationManager = [[CLLocationManager alloc] init]; 
      self.locationManager.delegate = self; 
      self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation; 
      self.locationManager.distanceFilter = 5; // specified in meters 
     } 

     self.locationHistory = [NSMutableArray arrayWithCapacity:kNumLocationHistoriesToKeep]; 
    } 

    return self; 
} 

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation { 
    // since the oldLocation might be from some previous use of core location, we need to make sure we're getting data from this run 
    if (oldLocation == nil) return; 
    BOOL isStaleLocation = [oldLocation.timestamp compare:self.startTimestamp] == NSOrderedAscending; 

    [self.delegate locationManagerDebugText:[NSString stringWithFormat:@"accuracy: %.2f", newLocation.horizontalAccuracy]]; 

    if (!isStaleLocation && newLocation.horizontalAccuracy >= 0.0f && newLocation.horizontalAccuracy < kRequiredHorizontalAccuracy) { 

     [self.locationHistory addObject:newLocation]; 
     if ([self.locationHistory count] > kNumLocationHistoriesToKeep) { 
      [self.locationHistory removeObjectAtIndex:0]; 
     } 

     BOOL canUpdateDistance = NO; 
     if ([self.locationHistory count] >= kMinLocationsNeededToUpdateDistance) { 
      canUpdateDistance = YES; 
     } 

     if ([NSDate timeIntervalSinceReferenceDate] - self.lastDistanceCalculation > kDistanceCalculationInterval) { 
      self.lastDistanceCalculation = [NSDate timeIntervalSinceReferenceDate]; 

      CLLocation *lastLocation = (self.lastRecordedLocation != nil) ? self.lastRecordedLocation : oldLocation; 

      CLLocation *bestLocation = nil; 
      CGFloat bestAccuracy = kRequiredHorizontalAccuracy; 
      for (CLLocation *location in self.locationHistory) { 
       if ([NSDate timeIntervalSinceReferenceDate] - [location.timestamp timeIntervalSinceReferenceDate] <= kValidLocationHistoryDeltaInterval) { 
        if (location.horizontalAccuracy < bestAccuracy && location != lastLocation) { 
         bestAccuracy = location.horizontalAccuracy; 
         bestLocation = location; 
        } 
       } 
      } 
      if (bestLocation == nil) bestLocation = newLocation; 

      CLLocationDistance distance = [bestLocation distanceFromLocation:lastLocation]; 
      if (canUpdateDistance) self.totalDistance += distance; 
      self.lastRecordedLocation = bestLocation; 
     } 
    } 
} 

Answer 1

事实证明，我上面发布的代码工作很好。问题发生在我的应用程序的不同部分。我意外地将距离从米转换为英里，而不是从米到公里。哎呀！

无论如何，希望我的帖子仍然有一些优点，因为我觉得这是一个非常可靠的例子，说明如何使用Core Location跟踪用户的距离。

Answer 2

您可能已将kRequiredHorizo​​ntalAccuracy设置得太低。如果历史中没有精确度为< kRequiredHorizo​​ntalAccuracy的位置，则忽略所有这些点并将距离加0。