测量两个位置之间的距离不准确

Question

am trying to get the distance between two location, but I always get wrong value. Here are the codes:

var startLoction: CLLocation!
var startLoction: CLLocation!

@IBAction func getCurrLocation(){
    startLoction = currLocation

}

func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        currLocation = locations.last!

        if currLocation.horizontalAccuracy > 0{

            var distance = CLLocationDistance(DBL_MAX)
            if let location = self.startLoction {
                distance = currLocation.distance(from: location)
                realTimeDistanceLabel.text = String(format: "%.2f", distance)
            }
        }
}

Problems: 1. When I stay still, the distance sometimes will increase, it may be a big number than 15 meters. It always starts at a big number 2. When I walk out 10 or 20 meters and then walk back straight, the distance sometimes increases but not decreases. 3. When I walk around a big circle, the distance goes to a bit more accurate value relatively.

I also tried to add currLocation.horizontalAccuracy > 0 && currLocation.horizontalAccuracy < 100 , and aslo tried prevLocation >= (currLocation.horizontalAccuracy * 0.5 from stackOverflow answer, still I cannot get a accurate value.

Any other ideas to make it right?

Thanks.

Answer 1

Core Location switch on when used, spend a period triangulating the device location such that it takes a while to settle down. But also you will find it can lose accuracy in certain locations/conditions and will try always to improve accuracy. The device will then be changing it's mind about "where you are located" and if it does this after your method

@IBAction func getCurrLocation() { ... }

is called, naturally it will appear as though the device has moved.

To reduce the effect of this occurring, you could test not just that currLocation.horizontalAccuracy > 0 (so it is a valid reading) but also that it is less than a given positive value (though this will bring it's own problem - see below). The current horizontal location of the device may be between plus or minus the radius of uncertainty as reported by the horizontalAccuracy property (the radius of uncertainty is always a positive number. If it is negative, all bets are off, the device is essentially saying "hang on, I can't say where I am with any certainty yet").

Actually though setting an upper bound for currLocation.horizontalAccuracy will demonstrate the problem, it probably won't be what you want because then your UI will only work under the condition Core Location knows accuracy is greater than x. Generally you wouldn't want to restrict the UI in this way.