Question

所以我正在处理iPhone GPS的一些准确性问题。我有一个使用位置的应用程序。

在委托方法locationManager: didUpdateToLocation: fromLocation:中，我正在返回一个位置。从一些研究来看，即使将desiredAccuracy属性设置为kCLLocationAccuracyBest，GPS在返回的第一个结果上也不总是准确的。

为了解决这个问题，我不会在stopUpdatingLocation返回newLocation:之前至少调用3次（这很快）。关于是否stopUpdatingLocation并返回newLocation，我还讨论了另外两个“要求”。我试过的一种方法是检查纬度和长度为newLocation并与oldLocation进行比较，如果这些不相同，则保持位置更新运行。我也尝试检查oldLocation和newLocation之间的距离，如果它不到20米，那就没事了。这两个都是通过返回至少3次运行来测试的。后一种方式不那么“严格”，因为如果用户在移动的车辆中，newLocation和oldLocation很难与100％完全相同。

现在，我的问题是，即使执行上述操作（基本上不接受某个位置，直到CLLocationManager上发生了一些更新并检查CLLocations之间的距离（或者它们是否是相同的）我在测试时有时会看到有些奇怪的位置结果。

如果我离开应用程序，进入Maps.app，使用GPS，然后打开多任务处理，强制退出我的应用程序，然后重新打开它以获得干净的启动，有时会修复。

人们习惯于解决同类问题的经验和可能的解决方案？评论和解决方案赞赏：）

Answer 1

我不记得我从哪个项目获得了以下代码，但这对我来说非常有效（我记得它来自WWDC 2010视频）。在我的代码中，我完全放弃了原始项目的评论，所以希望这会有所帮助。

- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
    // test the age of the location measurement to determine if the measurement is cached
    // in most cases you will not want to rely on cached measurements
    NSTimeInterval locationAge = -[newLocation.timestamp timeIntervalSinceNow];

    if (locationAge > 5.0) return;

    // test that the horizontal accuracy does not indicate an invalid measurement
    if (newLocation.horizontalAccuracy < 0) return;

    // test the measurement to see if it is more accurate than the previous measurement
    if (bestEffortAtLocation == nil || bestEffortAtLocation.horizontalAccuracy > newLocation.horizontalAccuracy) {
        // store the location as the "best effort"
        self.bestEffortAtLocation = newLocation;

        // test the measurement to see if it meets the desired accuracy
        //
        // IMPORTANT!!! kCLLocationAccuracyBest should not be used for comparison with location coordinate or altitidue 
        // accuracy because it is a negative value. Instead, compare against some predetermined "real" measure of 
        // acceptable accuracy, or depend on the timeout to stop updating. This sample depends on the timeout.
        //
        if (newLocation.horizontalAccuracy <= locationManager.desiredAccuracy) {
            // we have a measurement that meets our requirements, so we can stop updating the location
            // 
            // IMPORTANT!!! Minimize power usage by stopping the location manager as soon as possible.
            //
            [self stopUpdatingLocation:NSLocalizedString(@"Acquired Location", @"Acquired Location")];

            // we can also cancel our previous performSelector:withObject:afterDelay: - it's no longer necessary
            [NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(stopUpdatingLocation:) object:nil];
        }
    }
}

希望这有帮助！

通过Apple的“Locate Me”示例项目中的GetLocationViewController.m，可从以下位置获取：

https://developer.apple.com/library/content/samplecode/LocateMe/Introduction/Intro.html

Answer 2

从donkim的回答考虑更换这一行

[NSObject cancelPreviousPerformRequestsWithTarget:self selector:@selector(stopUpdatingLocation:) object:nil];

带行

[NSObject cancelPreviousPerformRequestsWithTarget: self];

CLLocationManager和准确性问题 - 任何经验？

2 个答案: