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 chip:
http://en.wikipedia.org/wiki/Moving_average Leonti On Tue, Aug 4, 2009 at 4:30 PM, Laszlo KREKACS<[email protected]> 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 > > _______________________________________________ > Openmoko community mailing list > [email protected] > http://lists.openmoko.org/mailman/listinfo/community > _______________________________________________ Openmoko community mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/community
