Hi,

I would like to calibrate the ARToolKit with the Matlab Toolbox Calibration
(http://www.vision.caltech.edu/bouguetj/calib_doc). I  know that  some of
you already asked for it in this mailing list. However, there was not a 
direct solution mentioned, until know. I tried to combine both, but
something isn’t right: 

Matlab delivers the following:

Focal Length:    fc (2x1) the focal distance (a unique value in  mm)
Principal point:  cc  (2x1) 
Skew:          alpha_c  (1x1) angle between the x and y pixel axes (assume
to be 90°)
Distortion:       kc (5x1)   radial and tangential distortions

and defines the intrinsic matrix:

fc(0)	alpha_c*fc(0)     cc(0)
0	     fc(1)	   cc(1)
0	      0		    1

the ARToolKit uses the following Matrix (without taking into account the
skew):

param.mat :

Sx*f  	0   X0							
0     Sy*f  Y0
0   	0   1   

Then comes what I did :

the Matlab Parameter into the param.mat:

fc(0)	      0             cc(0)
0	     fc(1)	   cc(1)
0	      0		    1	


the distortion

param.dist_factor[0] =	cc(0) //central point of distortion			
param.dist_factor[1] =	cc(1) //central point of distortion			
param.dist_factor[2] =	?;	//coefficient of distortion
param.dist_factor[3] =  ?;   //ratio of distortion

I am not sure about the values, I've chosen and what to put for
param.dist_factor[2],[3]?  

Thanks for any ideas!
Björn
  

>the ARToolKit uses the following Matrix (without taking into account the
>skew):
>
>param.mat :
>
>Sx*f  	0   X0							
>0     Sy*f  Y0
>0   	0   1   
>
>Then comes what I did :
>
>the Matlab Parameter into the param.mat:
>
>fc(0)	      0             cc(0)
>0	     fc(1)	   cc(1)
>0	      0		    1	

You can use skew parameter instead of 0.


>param.dist_factor[0] =	cc(0) //central point of distortion			
>param.dist_factor[1] =	cc(1) //central point of distortion			
>param.dist_factor[2] =	?;	//coefficient of distortion
>param.dist_factor[3] =  ?;   //ratio of distortion

These values are used in only two functions:
 int arParamObserv2Ideal( double dist_factor[4], double ox, double oy,
                         double *ix, double *iy )
 int arParamIdeal2Observ( double dist_factor[4], double ix, double iy,
                         double *ox, double *oy )

So easy way is to replace these two functions for Matlab distortion parameters.
I think the distortion model in ARToolKit is different from Matlab's one.

------------------------------------------------------------------
  Hirokazu Kato
  Graduate School of Engineering Science
  Osaka University                   Phone: +81-6-6850-6381
  Email: kato@s ...................     Fax: +81-6-6850-6341
  URL: http://www.sys.im.hiroshima-cu.ac.jp/people/kato/