# [racket] moby/phonegap/android: use acceleration or geolocation to derive velocity?

 From: keydana at gmx.de (keydana at gmx.de) Date: Wed Nov 3 11:24:02 EDT 2010 Previous message: [racket] Big dictionaries Next message: [racket] Math Guidance Messages sorted by: [date] [thread] [subject] [author]

```Thanks a lot for the hint! Can you perhaps detail a bit on the second part - how would I use GPS to handle the drift (also, if you knew a document accessible on the web describing this, that would be extremely helpful!)?

Regarding the first point, is it correct that "continuous" integration uses the following equation:

v(t1) = v(t0) + A * dt?

But then,  how do I combine the measures for the 3 axes - I found a formula that takes the square root of all three values squared, would that be correct?

Sigrid

Am 03.11.2010 um 00:18 schrieb Patrick Li:

> I think the most accurate thing you can probably do is integrate the accelerometer data to get velocity, and use the GPS data to handle the accumulating numerical drift. My friend used that approach for this thesis project for good results.
>   -Patrick
>
> On Tue, Nov 2, 2010 at 5:27 PM, keydana at gmx.de <keydana at gmx.de> wrote:
> Thanks Noel - the scale would be meters rather, but I somehow assumed that this might be too small-scale for GPS ...
>
> I guess I really ought to compare both measures, but for the GPS part, I wonder what would be the most "architecturally adequate" way to adapt 'world-updater' s contract to handle the additional geolocation field (and the other fields currently unused, possibly).
>
> ciao,
> Sigrid
>
>
>
> Am 02.11.2010 um 22:08 schrieb Noel Welsh:
>
> > I don't /really/ know, but isn't one reading from the accelerometer
> > and the other from GPS? The answer depends, I think, on the distance
> > over which you want to operate. If you want velocity from, e.g., hand
> > movements, the accelerometer is the way to go. If you want velocity
> > over large scale (metres, kms) use GPS.
> >
> > HTH,
> > N.
> >
> > On Tue, Nov 2, 2010 at 5:52 PM, keydana at gmx.de <keydana at gmx.de> wrote:
> >>
> >> Hi,
> >> I am wondering how best to calculate velocity in a moby/phonegap/android application.
> >> In general, would anyone have experience (or intuition) whether velocity might better be calculated from the acceleration values delivered by phonegap's Acceleration object, or directly be extracted from the Position object returned from Geolocation (it has a field 'velocity')?
>
> _________________________________________________