Re: touchscreen calibration again

Hi Zap,

Thanks a lot for proposing this!

>On Tue, 04 May 2004 09:11:28 +0200
>Michael Opdenacker <zumbi3@free.fr> wrote:
>
>
>
>>However, that's quite difficult to achieve, as the touchscreen is still
>>not very accurate in this area.
>>
>>
>I was thinking a lot about the non-linearity of the h2200 touchscreen, and
>came to the conclusion that unless there are tonns of different
>non-linear touchscreens (and h2200' is the only one I know of as of today),
>the linearization must be performed in the driver rather than in tslib.
>
Sounds the right way to do. I think we should create a h2200_ts driver
on top of shamcop_ts, as h2200 is not the only PDA with the HAMCOP chip.
This driver would contain all the specific stuff to interface with
tslib, as you said.

>Adding
>generic support for such touchscreens to tslib is a very complex task, it
>would be rather easy to create a static array containing the curves that Alain
>(if I'm not wrong) has put into that PDF and linearize the touchscreen in
>accordance to those curves. After that, tslib and older progs can perform
>calibration as usual, since they will see a rectangular field of coordinates.
>
>Since WinCE seems to work fine with the five-point calibration scheme, I think
>the shape of the top and bottom curves is quite standard amongst all iPAQ
>221x's, so it can be hard-coded into the driver.
>
Right!

>On one hand, since Alain's formulas seems to work more or less for everybody
>here, it seems like the touchscreen parameters are quite steady amongst
>different examplaires. On the other hand, we must be prepared to see 221x's
>with largely biased values - who knows what will happen, and even the
>parameters may change with time.
>
>
Exactly! Otherwise, there would be no need to calibrate... all this
would be hardcoded.

I guess we can start by harvesting more points for Lau, and then check
whether your simple model is valid on all the points that we gathered,
in parallel with Lau's work.

    :-)

    Michael.

-- 
Michael Opdenacker
http://opdenacker.org/