/* Fits a line into set of 2d points in a robust way (M-estimator technique) */
void cvFitLine2D( CvPoint2D32f* points, int count, int dist,
void *param, float reps, float aeps, float* line )
{
CvMat mat = cvMat( 1, count, CV_32FC2, points );
float _param = param != NULL ? *(float*)param : 0.f;
assert( dist != CV_DIST_USER );
cvFitLine( &mat, dist, _param, reps, aeps, line );
}
int main(int argc, const char * argv[]) {
IplImage* img = cvCreateImage( cvSize( 500, 500 ), 8, 3 );
CvRNG rng = cvRNG(-1);
cvNamedWindow( "fitline", 1 );
for(;;) {
char key;
int i, count = cvRandInt(&rng) % 100 + 1, outliers = count/5;
float a = cvRandReal(&rng) * 200;
float b = cvRandReal(&rng) * 40;
float angle = cvRandReal(&rng) * CV_PI;
float cos_a = cos(angle), sin_a = sin(angle);
CvPoint pt1, pt2;
CvPoint* points = (CvPoint*)malloc( count * sizeof(points[0]));
CvMat pointMat = cvMat( 1, count, CV_32SC2, points );
float line[4];
float d, t;
b = MIN(a*0.3, b);
// generate some points that are close to the line
for( i = 0; i < count - outliers; i++ ) {
float x = (cvRandReal(&rng)*2-1)*a;
float y = (cvRandReal(&rng)*2-1)*b;
points[i].x = cvRound(x*cos_a - y*sin_a + img->width/2);
points[i].y = cvRound(x*sin_a + y*cos_a + img->height/2);
}
// generate "completely off" points
for( ; i < count; i++ ) {
points[i].x = cvRandInt(&rng) % img->width;
points[i].y = cvRandInt(&rng) % img->height;
}
// find the optimal line
cvFitLine( &pointMat, CV_DIST_L1, 1, 0.001, 0.001, line );
cvZero( img );
// draw the points
for( i = 0; i < count; i++ ) {
cvCircle( img, points[i], 2, i < count - outliers ? CV_RGB(255, 0, 0) : CV_RGB(255,255,0), CV_FILLED, CV_AA, 0 );
}
d = sqrt((double)line[0]*line[0] + (double)line[1]*line[1]);
line[0] /= d;
line[1] /= d;
t = (float)(img->width + img->height);
pt1.x = cvRound(line[2] - line[0]*t);
pt1.y = cvRound(line[3] - line[1]*t);
pt2.x = cvRound(line[2] + line[0]*t);
pt2.y = cvRound(line[3] + line[1]*t);
cvLine( img, pt1, pt2, CV_RGB(0,255,0), 3, CV_AA, 0 );
cvShowImage( "fitline", img );
key = (char) cvWaitKey(0);
if( key == 27 ) break;
free( points );
}
cvDestroyWindow( "fitline" );
return 0;
}
