Ben Lau benlau at
Fri May 30 11:16:42 CEST 2008

On Thu, May 29, 2008 at 7:11 PM, Joerg Reisenweber <joerg at> wrote:
> Am Do  29. Mai 2008 schrieb boris.stender at
>> 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
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Two-finger input with a standard touch screen

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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