为什么我的 iPhone 应用程序首次启动时会获得额外的位置坐标点？

Question

我正在开发一个使用 CLLocationManager 的 iPhone 应用程序。当用户跑步时，它会在地图视图上显示跑步路径。我使用以下代码在 mapView 上绘制运行路径：

 double leastDistanceToRecord = 0.0000905;

 - (void) locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
if (newLocation.horizontalAccuracy >= 0) {
    if (!runoPath)
    {
        NSLog(@"in !runoPath if");
        // This is the first time we're getting a location update, so create
        // the RunoPath and add it to the map.
        runoPath = [[RunoPath alloc] initWithCenterCoordinate:newLocation.coordinate];
        [map addOverlay:runoPath];

        self.currentRunData = [[RunData alloc] init];

        [currentRunData startPointLocation:newLocation];    

        // On the first location update, zoom map to user location
        MKCoordinateRegion region = 
        MKCoordinateRegionMakeWithDistance(newLocation.coordinate, 1000, 1000);
        [map setRegion:region animated: NO];


    }
    else
    {
        // This is a subsequent location update.
        // If the runoPath MKOverlay model object determines that the current location has moved
        // far enough from the previous location, use the returned updateRect to redraw just
        // the changed area.

        double latitudeChange = fabs(newLocation.coordinate.latitude - oldLocation.coordinate.latitude);
        double longitudeChange = fabs(newLocation.coordinate.latitude - oldLocation.coordinate.longitude);
        if (latitudeChange > leastDistanceToRecord || longitudeChange > leastDistanceToRecord) {
            MKMapRect updateRect = [runoPath addCoordinate:newLocation.coordinate];
            if (!MKMapRectIsNull(updateRect))
            {
                // There is a non null update rect.
                // Compute the currently visible map zoom scale
                MKZoomScale currentZoomScale = map.bounds.size.width / map.visibleMapRect.size.width;
                // Find out the line width at this zoom scale and outset the updateRect by that amount
                CGFloat lineWidth = MKRoadWidthAtZoomScale(currentZoomScale);
                updateRect = MKMapRectInset(updateRect, -lineWidth, -lineWidth);
                // Ask the overlay view to update just the changed area.
                [runoPathView setNeedsDisplayInMapRect:updateRect];
            }
        //  [currentRunData updateLocation:oldLocation toNewLocation: newLocation];         
        }
        [currentRunData updateLocation:oldLocation toNewLocation: newLocation]; 

//  }
}
 }
 }

问题是，当我开始运行时，我得到了一些额外的点，然后由于这些点，我在 mapView 上得到了一条不反映实际运行的无关线。甚至当我在 iPhone 上安装该应用程序并首次运行时也会发生这种情况。我不知道为什么要添加这些额外的积分。有人能帮我吗？提前致谢。

Answer 1

您获得的第一个位置通常是缓存位置并且是旧的。您可以检查位置的存在时间，如果它是旧的（> 60 秒或其他），则忽略该位置更新。请参阅此处的答案。

--编辑-- 如果您仍然遇到问题，请将此代码放入 didUpdateToLocation: 并向我们展示 NSLog 的实际输出（您可以编辑您的问题并添加输出）：

NSTimeInterval age = -[newLocation.timestamp timeIntervalSinceNow]; 
NSLog(@"age: %0.3f sec, lat=%0.2f, lon=%0.2f, hAcc=%1.0f", 
      age, newLocation.coordinate.latitude, newLocation.coordinate.longitude,
      newLocation.horizontalAccuracy);