使用 CLLocationManager 计算准确的总步行/跑步距离时遇到问题

Question

我正在尝试构建一个 iOS 应用程序，以显示跑步或步行时的总行驶距离。我已经阅读并重新阅读了所有我能找到的文档，但我无法想出一些能提供准确总距离的东西。

与 Nike+ GPS 或 RunKeeper 相比，我的应用始终报告更短的距离。他们一开始会报告相同的情况，但随着我不断前进，我的应用程序与其他正在运行的应用程序的价值会逐渐漂移。

例如，如果我步行 0.3 公里（通过我的汽车里程表验证），Nike+ GPS 和 RunKeeper 每次都会报告 ~.3 公里，但我的应用程序会报告 ~.13 公里。 newLocation.horizo​​ntalAccuracy 始终为 5.0 或 10.0。

这是我正在使用的代码。我错过了一些明显的东西吗？关于如何改进这一点以获得更准确的读数的任何想法？

#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，我在上面发布的代码效果很好。问题恰好出在我的应用程序的不同部分。我不小心将距离从米转换为英里，而不是从米转换为公里。糟糕！

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示例，说明如何使用核心位置跟踪用户的距离。

Answer 2

您可能将 kRequiredHorizo​​ntalAccuracy 设置得太低。如果历史记录中没有准确度