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,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我能找到的所有文档,但是我无法想出能够给出准确总距离的东西.

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逐渐变化.

例如,如果我走了0.3公里(通过我的汽车里程表验证),Nike + GPS和RunKeeper每次报告约.3公里,但我的应用程序将报告〜.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 有关如何改进这一点以获得更准确读数的任何想法？

#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,我上面发布的代码效果很好.问题碰巧发生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,因为我觉得它是如何跟踪用户与Core Location的距离的一个非常可靠的例子.