CLLocationManager responsiveness

Question

I have an app that revolves around the device\'s GPS and the information that comes from it. It is important that the location data be accurate and up-to-date. I know that t

Answer 1

OK, a couple of things could improve your lag. First of all, use kCLLocationAccuracyBestForNavigation always. There is no real battery usage difference between that and kCLLocationAccuracyBest, they both use the GPS at top speed. The main difference is in the post-processing that Apple does.

Second, there is no need to filter for speed == 0. Apple already does that filtering: if your speed from the GPS drops below a certain threshold (about 4 km/h), the OS assumes you are standing still, and it substitutes the same location value for all subsequent samples. It does that until it thinks you are moving again. I assume they do that to avoid "jittering" on the map when you are standing still. In fact, speed drops to 0 already for the last real value of a sequence of "standing-still" values, so if you filter on speed == 0 than you are missing one real GPS sample.

Unfortunately, they is no way to avoid that filtering and get real GPS samples. I talked to Apple about it, and their response was that they are not going to change the behaviour. kCLLocationAccuracyBestForNavigation does less aggressive filtering than kCLLocationAccuracyBest, so it's best to use that.

Third, you probably are already doing this, but make sure that you call "setNeedsDisplay" on your view right from the "didUpdateFromLocation:", to make sure that the map is actually redrawn.

If you do all that, you should have a lag of about 1 second. If you want to improve on the 1 second than you can try to use predictive techniques. From the last two locations, and the given speed, you can calculate where the next location is likely to be, and already display that location. I have had mixed results with that. It works well for fast movement that does not change speed suddenly, like driving a car. It works less well for slower movement like walking or biking.