calibrate.c

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/*
 * File Name: calibrate.c
 */

/*
 * This file is part of gtktscal.
 *
 * gtktscal is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * gtktscal is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */
 
/*
 * This code is originally from:
 * 
 *  tslib/tests/ts_calibrate.c
 *
 *  Copyright (C) 2001 Russell King.
 *
 * Modifications:
 *
 *  Copyright (C) 2008 iRex Technologies B.V.
 */

#include <stdio.h>

#include "calibrate.h"

extern int flag_debug;

int perform_calibration(calibration *cal) {
   int j;
   float n, x, y, x2, y2, xy, z, zx, zy;
   float det, a, b, c, e, f, i;
   float scaling = 65536.0;

// Get sums for matrix
   n = x = y = x2 = y2 = xy = 0;
   for(j=0;j<5;j++) {
      n += 1.0;
      x += (float)cal->x[j];
      y += (float)cal->y[j];
      x2 += (float)(cal->x[j]*cal->x[j]);
      y2 += (float)(cal->y[j]*cal->y[j]);
      xy += (float)(cal->x[j]*cal->y[j]);
   }

// Get determinant of matrix -- check if determinant is too small
   det = n*(x2*y2 - xy*xy) + x*(xy*y - x*y2) + y*(x*xy - y*x2);
   if(det < 0.1 && det > -0.1) {
      fprintf(stderr, "ts_calibrate: determinant is too small -- %f\n",det);
      return 0;
   }

// Get elements of inverse matrix
   a = (x2*y2 - xy*xy)/det;
   b = (xy*y - x*y2)/det;
   c = (x*xy - y*x2)/det;
   e = (n*y2 - y*y)/det;
   f = (x*y - n*xy)/det;
   i = (n*x2 - x*x)/det;

// Get sums for x calibration
   z = zx = zy = 0;
   for(j=0;j<5;j++) {
      z += (float)cal->xfb[j];
      zx += (float)(cal->xfb[j]*cal->x[j]);
      zy += (float)(cal->xfb[j]*cal->y[j]);
   }

// Now multiply out to get the calibration for framebuffer x coord
   cal->a[0] = (int)((a*z + b*zx + c*zy)*(scaling));
   cal->a[1] = (int)((b*z + e*zx + f*zy)*(scaling));
   cal->a[2] = (int)((c*z + f*zx + i*zy)*(scaling));

   if (flag_debug)
     fprintf(stderr, "%f %f %f\n",(a*z + b*zx + c*zy),
        (b*z + e*zx + f*zy),
        (c*z + f*zx + i*zy));

// Get sums for y calibration
   z = zx = zy = 0;
   for(j=0;j<5;j++) {
      z += (float)cal->yfb[j];
      zx += (float)(cal->yfb[j]*cal->x[j]);
      zy += (float)(cal->yfb[j]*cal->y[j]);
   }

// Now multiply out to get the calibration for framebuffer y coord
   cal->a[3] = (int)((a*z + b*zx + c*zy)*(scaling));
   cal->a[4] = (int)((b*z + e*zx + f*zy)*(scaling));
   cal->a[5] = (int)((c*z + f*zx + i*zy)*(scaling));

   if (flag_debug)
     fprintf(stderr, "%f %f %f\n",(a*z + b*zx + c*zy),
        (b*z + e*zx + f*zy),
        (c*z + f*zx + i*zy));

// If we got here, we're OK, so assign scaling to a[6] and return
   cal->a[6] = (int)scaling;
   return 1;
/* 
// This code was here originally to just insert default values
   for(j=0;j<7;j++) {
      c->a[j]=0;
   }
   c->a[1] = c->a[5] = c->a[6] = 1;
   return 1;
*/

}