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PO
 

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    <p>Even if you don't like the built-in velocity stuff, it's simple to roll your own.</p> <p>Speed is distance over time, right?</p> <p>If you've got two <code>CLLocation</code>s, you can do:</p> <pre><code>CLLocationDistance distance = [aLocation distanceFromLocation:bLocation]; </code></pre> <p><code>distance</code> is now a float of the distance between those two points, in meters. And those two <code>CLLocations</code> have <code>timestamp</code> properties too, right? Containing NSDate objects. Well...</p> <pre><code>NSTimeInterval timediff = [aDate timeIntervalSinceDate:bDate]; </code></pre> <p><code>timediff</code> is the difference in seconds.</p> <p>So your average speed between those points in meters per second is <code>distance</code> over <code>timediff</code>. You can now calculate instantaneous speed as accurately as the frequency with which you're getting location updates.</p> <p>I imagine this is all that's happening to get the <code>speed</code> property of the CLLocation object you're getting handed. But hey, you want to be closer to the math, go right ahead.</p> <p>From there, you can convert to whatever units you like. There are 1609.344 meters in a mile. There are 3600 seconds in an hour. </p> <p>NOW: This is as flawed as any pure GPS-based speed calculation, in that you're not going to get perfectly spaced tick-marks of location updates, and sometimes they're going to be way wrong. If you lose GPS signal and the device falls back to cell tower triangulation, it might put you WAY off the road somewhere, and it's going to look like you strapped on a rocket pack to get way <em>over there</em> that fast.</p>
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    1. POIssue in finding the speed when using CLLocationManager
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    1. USDan Ray
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    1. COHi Dan,As you mentioned i have already tried with my own code for calculating the speed.My problem is i get the speed which is approximate,but there is a great deflection in speed even the vehicle is stationary.Is there any filtering techniques that can be used to avoid the deflection when the vehicle is stationary..
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    2. COWell, yeah, I mean you could sanity-check your CLLocations on the way in. You could discard locations that are suddenly a lower accuracy than you've been seeing. You could throw out locations that result in impossible speeds or impossible delta-v (I mean, it's probably not real likely you'd suddenly go from 40 to 400 mph, is it?).
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