c++ - 如果失败，OpenCV camshift 返回值

Question

我是 opencv 的新手，所以我想知道如果 CamShift 无法跟踪任何旋转矩形，返回值是多少。我应该如何处理这个？我的意思是，在现实中可能会丢失跟踪目标。我应该如何在 C++ 中捕捉到这个错误？

Answer 1

读取位于 modules\video\scr\ 的 camshift.cpp

例如 cvCamShift()：

cvCamShift( const void* imgProb, CvRect windowIn,
            CvTermCriteria criteria,
            CvConnectedComp* _comp,
            CvBox2D* box )
{
    const int TOLERANCE = 10;
    CvMoments moments;
    double m00 = 0, m10, m01, mu20, mu11, mu02, inv_m00;
    double a, b, c, xc, yc;
    double rotate_a, rotate_c;
    double theta = 0, square;
    double cs, sn;
    double length = 0, width = 0;
    int itersUsed = 0;
    CvConnectedComp comp;
    CvMat  cur_win, stub, *mat = (CvMat*)imgProb;

    comp.rect = windowIn;

    mat = cvGetMat( mat, &stub );

    itersUsed = cvMeanShift( mat, windowIn, criteria, &comp );
    windowIn = comp.rect;

    windowIn.x -= TOLERANCE;
    if( windowIn.x < 0 )
        windowIn.x = 0;

    windowIn.y -= TOLERANCE;
    if( windowIn.y < 0 )
        windowIn.y = 0;

    windowIn.width += 2 * TOLERANCE;
    if( windowIn.x + windowIn.width > mat->width )
        windowIn.width = mat->width - windowIn.x;

    windowIn.height += 2 * TOLERANCE;
    if( windowIn.y + windowIn.height > mat->height )
        windowIn.height = mat->height - windowIn.y;

    cvGetSubRect( mat, &cur_win, windowIn );

    /* Calculating moments in new center mass */
    cvMoments( &cur_win, &moments );

    m00 = moments.m00;
    m10 = moments.m10;
    m01 = moments.m01;
    mu11 = moments.mu11;
    mu20 = moments.mu20;
    mu02 = moments.mu02;

    if( fabs(m00) < DBL_EPSILON )
        return -1;

    inv_m00 = 1. / m00;
    xc = cvRound( m10 * inv_m00 + windowIn.x );
    yc = cvRound( m01 * inv_m00 + windowIn.y );
    a = mu20 * inv_m00;
    b = mu11 * inv_m00;
    c = mu02 * inv_m00;

    /* Calculating width & height */
    square = sqrt( 4 * b * b + (a - c) * (a - c) );

    /* Calculating orientation */
    theta = atan2( 2 * b, a - c + square );

    /* Calculating width & length of figure */
    cs = cos( theta );
    sn = sin( theta );

    rotate_a = cs * cs * mu20 + 2 * cs * sn * mu11 + sn * sn * mu02;
    rotate_c = sn * sn * mu20 - 2 * cs * sn * mu11 + cs * cs * mu02;
    length = sqrt( rotate_a * inv_m00 ) * 4;
    width = sqrt( rotate_c * inv_m00 ) * 4;

    /* In case, when tetta is 0 or 1.57... the Length & Width may be exchanged */
    if( length < width )
    {
        double t;

        CV_SWAP( length, width, t );
        CV_SWAP( cs, sn, t );
        theta = CV_PI*0.5 - theta;
    }

    /* Saving results */
    if( _comp || box )
    {
        int t0, t1;
        int _xc = cvRound( xc );
        int _yc = cvRound( yc );

        t0 = cvRound( fabs( length * cs ));
        t1 = cvRound( fabs( width * sn ));

        t0 = MAX( t0, t1 ) + 2;
        comp.rect.width = MIN( t0, (mat->width - _xc) * 2 );

        t0 = cvRound( fabs( length * sn ));
        t1 = cvRound( fabs( width * cs ));

        t0 = MAX( t0, t1 ) + 2;
        comp.rect.height = MIN( t0, (mat->height - _yc) * 2 );

        comp.rect.x = MAX( 0, _xc - comp.rect.width / 2 );
        comp.rect.y = MAX( 0, _yc - comp.rect.height / 2 );

        comp.rect.width = MIN( mat->width - comp.rect.x, comp.rect.width );
        comp.rect.height = MIN( mat->height - comp.rect.y, comp.rect.height );
        comp.area = (float) m00;
    }

    if( _comp )
        *_comp = comp;

    if( box )
    {
        box->size.height = (float)length;
        box->size.width = (float)width;
        box->angle = (float)((CV_PI*0.5+theta)*180./CV_PI);
        while(box->angle < 0)
            box->angle += 360;
        while(box->angle >= 360)
            box->angle -= 360;
        if(box->angle >= 180)
            box->angle -= 180;
        box->center = cvPoint2D32f( comp.rect.x + comp.rect.width*0.5f,
                                    comp.rect.y + comp.rect.height*0.5f);
    }

    return itersUsed;
}