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POI'm getting a callback with latitude and longitude, how can I best calculate "current speed", and other derived values?
 

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  1. POI'm getting a callback with latitude and longitude, how can I best calculate "current speed", and other derived values?
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    <p>(I think this question is platform independent, but I happen to be coding for a Nexus One).</p> <p>About "current speed": I'm getting a callback every second or so telling me what my current latitude and longitude are. I can calc the distance between the current location and the previous location, so I can keep track of cumulative distance and cumulative time. With that I can say what the average speed has been for the ENTIRE trip.</p> <p>But how do I calc current speed? I suspect I need to use the most recent N samples, right? Am I thinking about this the right way? What's a good rule of thumb for N? How many samples, or how many seconds back?</p> <p>About "stop time": If I'm just standing still, I can still get slightly different latitudes and longitudes reported to me, right? So, deciding that I'm not really moving means saying something like, "the previous X locs have all been within Y meters of each other", right? Am I thinking about this the right way? What's a good rule of thumb for X and Y?</p> <p>Even about "distance": Will I be understating it because I'm literally cutting corners? Is there an algorithm or a rule of thumb, for determining when I'm "turning" and should I add in a little fudge?</p> <p>EDIT: I APOLOGIZE: I feel bad about wasting people's time and good will, but sadly, the device <em>IS</em> giving me speed. I thought it wasn't because in the emulator it wasn't, but on the real device it is. Thanks everybody. There's still some rule-of-thumb code I need to write, but speed was the biggest challenge.</p> <p>EDIT: I retract the apology. In my original question I wrote that distance too is a derived value. If I just use the raw GPS data, I will be overstating distance because of the inaccuracies. I might be walking a straight line, but the raw GPS lat/long will wobble, so if I calc total distance by measuring the distance between the points, I will be overstating it. Here's some links that are related to this problem.</p> <p><a href="https://stackoverflow.com/questions/1134579/smooth-gps-data">Smooth GPS data</a><br> <a href="http://www.cs.unc.edu/~welch/kalman/Levy1997/index.html" rel="nofollow noreferrer">http://www.cs.unc.edu/~welch/kalman/Levy1997/index.html</a><br> <a href="https://stackoverflow.com/questions/1849928/how-to-intelligently-degrade-or-smooth-gis-data-simplifying-polygons">How to intelligently degrade or smooth GIS data (simplifying polygons)?</a><br> <a href="https://stackoverflow.com/questions/204184/how-to-smooth-data-and-calculate-line-gradient">How to &#39;smooth&#39; data and calculate line gradient?</a> </p>
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    1. COif you are taking this data from a device, particularly one using the Sirf chipset then velocity will probably be provided as part of the returned data.
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      1. USSteve Weet
 

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