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 应用程序来显示跑步或步行时的总距离。我已经阅读并重新阅读了我能找到的所有文档，但我无法想出一些可以给我准确的总距离的东西。

与 Nike+ GPS 或 RunKeeper 相比，我的应用程序始终报告较短的距离。他们一开始会报告相同的情况，但随着我继续前进，我的应用程序与其他正在运行的应用程序的值逐渐发生变化。

例如，如果我步行 0.3 公里（通过汽车里程表验证），Nike+ GPS 和 RunKeeper 每次都会报告约 0.3 公里，但我的应用程序将报告约 0.13 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有什么想法吗？

#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，我上面发布的代码效果很好。问题恰好出现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。哎呀！

不管怎样，希望我的帖子仍然有一些优点，因为我觉得这是一个关于如何使用核心位置跟踪用户距离的非常可靠的例子。

Answer 2

您可能将 kRequiredHorizo​​ntalAccuracy 设置得太低。如果历史中没有位置的准确度<； kRequiredHorizo​​ntalAccuracy，然后忽略所有这些点并将距离添加 0。