[Fun] Have you ever wondered of the GPS chip accuracy?

Leonti Bielski prishelec at gmail.com
Wed Aug 5 01:03:07 CEST 2009

I think the chip accuracy has nothing to do with it. As I can see from
the picture, right now you just have reported speed at time points
connected with straight lines.
This is why it's so "hairy" - because it's a raw speed at 1 second
rate. What you want to do is to use some kind of filter, for example
"moving average" - it will make your data look like data from the



On Tue, Aug 4, 2009 at 4:30 PM, Laszlo
KREKACS<laszlo.krekacs.list at gmail.com> wrote:
> Hi!
> When I was on holiday, I ended up to write a gps app,
> and I wondered how to measure speed exactly.
> My first attempt was, that I take the gps coordinates
> every second, and I calculate how many meters I
> walked/biked.
> Then I discovered, that fso reports speed  too (although
> in "knot" units), after a bit of research, I multiplied the
> knots with 1.852 to finally have my speed in km/hour.
> Then I compared the two results, and it was interesting
> enough, that I thought would be fun to share with you too.
> Here is the generated svg data:
> http://laszlo.krekacs.googlepages.com/doh.svg
> On the horizontal axe you can see the time (in 10 sec unit,
> and every minutes and 10 minutes has a longer line).
> On the vertical axe there is the speed in km/h.
> There are some horizontal area, which indicates speed
> limits (I was biking):
> greenish: 0-5km/h
> yellowish: 5-10km/h
> red/lila: 10-15km/h
> blueish: 15-20km/h
> The black curve is the calculated speed based on the
> reported gps coordinates.
> The green curve is the speed what the gps chip recorded.
> The duration of the whole trip was 15 min, as you can read
> from the graphicon.
> I think the pictures talks for himself, but everybody can see,
> that the calculated speed is really "hairy" compared to
> the reported speed by the gps chip.
> If anybody interested, I can share the data (from where
> the graph was generated)...
> I got two questions regarding the gps chip, maybe someone
> can answer me:
> - is there some settings, where I can fine-tune the gps
> chip? (I think what is the method to calculate the average speed?
> Is it adjustable?)
> - Is there a way to ask for gps coordinates faster then one second?
> (for running 0.1 sec would be awesome). And why the time is
> only reported in sec unit? (not fraction of the second)
> 1249424982.764385 vs. 1249424982
> Is it a limitation of the gps chip?
> Best regards,
>  Laszlo
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