multi-tutch?

[Rahul Joshi]

If I am to understand this thread discussion correctly, does it mean there
is no public algo for multi-point touch sensing yet??
With so much of work done on projects like MS Surface, iPhone, the Jeff Han
stuff.. and recently HTC Diamond, I took it for granted that it must already
be there among the large resource pool of opensource developers.

Rahul J


On Fri, May 30, 2008 at 2:46 PM, Ben Lau <benlau at embedded.hk> wrote:

> On Thu, May 29, 2008 at 7:11 PM, Joerg Reisenweber <joerg at openmoko.org>
> wrote:
> > Am Do  29. Mai 2008 schrieb boris.stender at gmx.de:
> >> Hi Joerg,
> >> as it seems that my mail did not reach the community list (I am not a
> > subscriber, just monitoring the archives) may I ask you directly the
> question
> > regarding "multi tutch" :-) . See below:
> >>
> >>
> >> Hi all,
> >> if the geometric average point is returned if multiple points are
> touched
> > wouldn't it be possible to have a fake multi touch, e.g., by doing the
> > following:
> >>
> >> Press point A
> >> -> Vector A is returned
> >> Additionally press desired point B
> >> -> X = (A+B)/2 is returned
> >> -> calculate B = 2*X-A
> >>
> >> Questions:
> >> Would this be managable?
> >> What time difference would be required between first and second (and
> > third ...) touch, to recognize such a multi-touch action and reliable
> > distinguish it from a single touch at position X?
> >>
> >> And one more comment: If that would work you could also detect
> multi-touch
> > gestures (even if limited), e.g., use the first point statically (maybe a
> > focus centre) and handle the second point dynamically (maybe for zooming
> in
> > and out).
> >>
> >>
> >> Boris
> >
> >
> > there are two resistors in the touchpad, one for X and one for Y. We only
> see
> > them changing on a touch, thus giving us the coords. A concurrent second
> > touch just changes the R values even more, but we get no info about
> whether
> > we touched a second point or we moved the finger. So what you suggest is
> a
> > gesture recognition. Things become nasty because even the "geometric
> middle"
> > isn't true but depends on pressure of one to pressure of other touchpoint
> > etc.
> > You really get too few info out of the device to do anything reasonable
> with
> > it beyond singletouch (at least that's the way it is now. I plan to see
> > whether we can exploit dynamic pulse response of this design to get some
> > additional info. Same way you're testing cat5-cable for breaks. Don't
> hold
> > your breath though, chances are bad. And it's not on top of my todo-list)
> >
> > cheers
> > jOERG
> >
> > _______________________________________________
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> > community at lists.openmoko.org
> > http://lists.openmoko.org/mailman/listinfo/community
> >
> >
>
> Two-finger input with a standard touch screen
> http://portal.acm.org/citation.cfm?id=1294239
>
> This paper introduces a method to detect two fingers using a
> "standard" touch screen. I haven't ready it deeply so I can not say is
> it applicable on OpenMoko platform , but I think it is worth to study.
>
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