iOS locationManager - car gauge delay - ios

Question

I am trying to make an app thats shows your speed (velocity) on a gauge (like in a car).
the problem I have is that CLlocationManager delegate method didUpdateLocations gives me a read of the location and the speed only once a second and so if I accelerate the car too fast i get delay with the needle position on the gauge.
for example: I get the speed 13 m/s and after one second i get 26 m/s and so the needle in the UI goes to 13 m/s and waits there for a second and only then goes to 26 m/s. so i get a non continuous movement of needle in the UI.
from reading other question i understood that i can't control the sample rate that I get from CLlocation and that i can't tell him to give me a read every 0.25 sec (with different values).
1. is is true?
2. how can I solve it so it will look good to the user?
//in viewdidload:
self.locationManager.delegate = self
self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation
self.locationManager.distanceFilter = kCLDistanceFilterNone
if versionNum == 8 {
self.locationManager.requestAlwaysAuthorization()
}
self.locationManager.startUpdatingLocation()
func locationManager(manager: CLLocationManager!, didUpdateLocations locations: [AnyObject]!) {
println(locations)
var loc = locations.last as! CLLocation
var speed = loc.speed
var time = loc.timestamp
var hour = getCurrentHour(time)
println("hour inside manager: \(hour)")
if hour == 18 && self.isItDay {
self.currentTimeHour = hour
self.setDayBool()
self.setRightImg()
}
else if hour == 6 && !self.isItDay {
self.currentTimeHour = hour
self.setDayBool()
self.setRightImg()
}
if self.unit == "MPH" {
speed = speed * 3.280839895013123
}
if speed >= 0 {
self.speedLabel.text = "\(Int(speed))"
self.animateNeedle(CGFloat(speed))
}
println("speed: \(speed)")
}
func animateNeedle(speed : CGFloat) {
var rotation : CGFloat = 0
if self.unit == "KMH" {
rotation = (speed * 4) - 5
}
else if self.unit == "MPH" {
rotation = speed + ((speed / 3) - 5)
}
if let trans = self.needleImg.layer.presentationLayer() {
self.currentValue = self.needleImg.layer.presentationLayer().valueForKeyPath("transform.rotation") as! Float
}
println(currentValue)
let rotateAnimation = CABasicAnimation(keyPath: "transform.rotation")
rotateAnimation.fillMode = kCAFillModeBoth
rotateAnimation.removedOnCompletion = false
rotateAnimation.fromValue = currentValue
rotateAnimation.toValue = self.degToRad(rotation)
rotateAnimation.duration = 0.3
self.needleImg.layer.addAnimation(rotateAnimation, forKey: "transform.rotation")
}

Answer 1

As Lefteris says, you should set your distance filter to 0. You should also select kCLLocationAccuracyBest as the desiredAccuracy property of your location manager.
iOS GPS is rather crude in any case, so I doubt if either of those things will help a whole lot.
I would suggest animating your speedometer needle from it's old position to the new. A duration of .2 - .3 seconds should be enough to create the impression of movement without taking so long that it interferes with keeping the needle position current.
You can use UIView animation methods like animateWithDuration:animations, or Core Animation. Core Animation is a lot harder to use but offers more options.

Answer 2

You need to set the distance filter that notify changes:
/* Notify changes when device has moved x meters.
* Default value is kCLDistanceFilterNone: all movements are reported.
*/
self.locationManager.distanceFilter = 10.0f;
From Apple Documentation:
For more option look at this full example:
self.locationManager = [CLLocationManager new];
self.locationManager.purpose = #"Tracking your movements on the map.";
self.locationManager.delegate = self;
/* Pinpoint our location with the following accuracy:
*
* kCLLocationAccuracyBestForNavigation highest + sensor data
* kCLLocationAccuracyBest highest
* kCLLocationAccuracyNearestTenMeters 10 meters
* kCLLocationAccuracyHundredMeters 100 meters
* kCLLocationAccuracyKilometer 1000 meters
* kCLLocationAccuracyThreeKilometers 3000 meters
*/
self.locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters;
/* Notify changes when device has moved x meters.
* Default value is kCLDistanceFilterNone: all movements are reported.
*/
self.locationManager.distanceFilter = 10.0f;
/* Notify heading changes when heading is > 5.
* Default value is kCLHeadingFilterNone: all movements are reported.
*/
self.locationManager.headingFilter = 5;
// update location
if ([CLLocationManager locationServicesEnabled]){
[self.locationManager startUpdatingLocation];
}

Answer 3

You need to set the distance filter to 0:
self.locationManager.distanceFilter = kCLDistanceFilterNone;
Also as Massimo mentioned above, you should also change the desired accuracy:
self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;