Name for error resulting from GPS sampling on curves?
August 18, 2011 6:06 AM   Subscribe

Is there a proper name for errors in distance calculated by GPS logs resulting from a curving path not receiving enough samples to define it and thus being shortened?

I do a lot of mountain biking and have taken to using a GPS to log my distance. Typically I use a 1 second sample rate, but I find that some tight, fast, curvy parts of trails don't seem to be logged because two subsequent samples occur just before and after a curve, smoothing it out.

Is there a proper term for this sort of error? I've been referring to it as a "chording error" because it results in the distance measurement being taken based on a rather substantial chord of the curve.

(Please note, I understand that there will always be some amount of chording on curves simply because GPS-based measurement is done via discrete samples. I'm just trying to better understand the issue and the terms used to describe it.)
posted by c0nsumer to Technology (7 answers total) 1 user marked this as a favorite
Would the term possibly be 'aliasing' instead?
posted by c0nsumer at 6:09 AM on August 18, 2011

You could say that the error results from linear interpolation. When perhaps you should be doing a spline interpolation?
posted by vacapinta at 6:15 AM on August 18, 2011

I'd definitely say it's aliasing. This is a basically a problem of undersampling, and aliasing is what happens when you don't sample data at a high enough rate.
posted by RobotNinja at 6:25 AM on August 18, 2011

Thanks, RobotNinja. That definitely sounds like it.
posted by c0nsumer at 6:56 AM on August 18, 2011

lol...this is exactly how fractals were discovered!...Benoit Mandelbrot noticed the vast discrepancies between the measurements of the english coastline from various atlases. basically, the shorter your ruler, the longer your measurement. (get down to the level where you are measuring around pebbles and it becomes almost infinitely long...) I would call it "coastal paradox"
posted by sexyrobot at 8:15 AM on August 18, 2011 [1 favorite]

Amongst runners (in my group at least) it's "corner cutting".
posted by trialex at 2:59 PM on August 18, 2011

If you want to sound all fancy when complaining about this problem you can mention that you should have obeyed the Nyquist Criterion.
posted by RobotNinja at 8:59 PM on August 18, 2011

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