Re: Some help understanding tslib calibration math?

[jassi brar <jassi_singh_brar@xxxxxxxxx>]

   I think u need to look at
http://www.embedded.com/story/OEG20020529S0046 
  the 7th variable 's' is to scale the equation :D

regards,
jassi

--- Marc Singer <elf@xxxxxxxxx> wrote:
> I've found that the tslib patch for the qt 2.3.10
> doesn't properly
> calibrate my touchscreen.  The code from
> ts_calibrate (tslib) does.
> Yet, I don't completely understand the ts_calibrate
> algorithm.  I'd
> appreciate some pointers for comprehending the math.
> 
> What I gather so far is that the calibration data is
> a matrix.
> 
>             | a  d  1 |
> | x y 1 | * | b  e  1 | / s -> | u v 1 |
>             | c  f  1 |
> 
> where x and y are the touchscreen coordinates
> returned by the kernel
> driver and u v are screen coordinates for the touch
> location.  The
> coefficients a, b, c, d, e, f and s are the seven
> coefficients from
> the pointercal file.
> 
> I also believe that the reason that the
> qt-2.3.10-tslib patch doesn't
> work with my target hardware has to do with the
> assumption that the X
> direction of the touchscreen is the X direction of
> the LCD display.
> 
> Here's an example pointercal file that works.
> 
>   26 -18897 17649214 25450 -140 -2287500 65536
> 
> The qt-2.3.10-tslib patch code always emits 0's for
> the second and
> fourth coefficients.
> 
> Guidance will be appreciated.
> 
> Cheers.
> 
>
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