我正在尝试构建一个iOS应用程序,它可以显示跑步或步行时的总里程。我已经一遍又一遍地阅读了我能找到的所有文档,但我在想出一个准确的总距离时遇到了麻烦。
与Nike+ GPS或RunKeeper相比,我的应用程序总是报告更短的距离。他们一开始会报告相同的,但随着我的不断移动,我的应用程序相对于其他运行中的应用程序的价值逐渐漂移。
例如,如果我步行.3公里(由我的汽车里程表验证),Nike+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.horizontalAccuracy始终为5.0或10.0。
这是我正在使用的代码。我是不是漏掉了什么明显的东西?有什么想法我可以改进这一点,以获得更准确的读数?
#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;
}
}
}
发布于 2012-01-09 22:28:06
事实证明,我在上面发布的代码工作得很好。问题恰好出现在我的应用程序的另一个部分。我意外地将距离从米转换为英里,而不是从米转换为公里。糟了!
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很好的例子,说明了如何使用Core Location跟踪用户的距离。
发布于 2012-01-09 02:15:06
您可能将kRequiredHorizontalAccuracy设置得太低了。如果历史记录中没有accuracy < kRequiredHorizontalAccuracy的位置,则忽略所有这些点并将距离添加0。
https://stackoverflow.com/questions/8779074
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