Question

I am using the CoreLocation framework to get my speed and distance to calculate average speed.

On the first update that CoreLocation sends out, it shows negative values for both speed and distance traveled. How can I fix this?

Speed is locationController.locationManager.location.speed where locationController holds my CoreLocation delegate. Distance is calculated by taking the old location and the new location and calculating distance.

//Distance
- (void)locationManager:(CLLocationManager *)manager
    didUpdateToLocation:(CLLocation *)newLocation
           fromLocation:(CLLocation *)oldLocation
{
    // make sure the old and new coordinates are different
    if ((oldLocation.coordinate.latitude != newLocation.coordinate.latitude) &&
        (oldLocation.coordinate.longitude != newLocation.coordinate.longitude))
    {         
        mDistance = [newLocation distanceFromLocation:oldLocation];
    }
}

Answer 1

The data returned by Core Location may be invalid for a number of reasons. Before you use the data, run this method to see if it is valid.

// From http://troybrant.net/blog/2010/02/detecting-bad-corelocation-data/
- (BOOL)isValidLocation:(CLLocation *)newLocation
        withOldLocation:(CLLocation *)oldLocation 
{
    // filter out nil locations
    if (!newLocation){
        return NO;
    }
    // filter out points by invalid accuracy
    if (newLocation.horizontalAccuracy < 0){
        return NO;
    }
    // filter out points that are out of order
    NSTimeInterval secondsSinceLastPoint = [newLocation.timestamp 
                                            timeIntervalSinceDate:oldLocation.timestamp];
    if (secondsSinceLastPoint < 0){
        return NO;
    }
    // filter out points created before the manager was initialized
    NSTimeInterval secondsSinceManagerStarted = [newLocation.timestamp 
                                                 timeIntervalSinceDate:locationManagerStartDate];
    if (secondsSinceManagerStarted < 0){
        return NO;
    }
    // newLocation is good to use
    return YES;
}