Function ClassicDescSearch

jni/stasm/classicdesc.cpp:235–289

// function and its callees do not modify any data that is not on the stack.

void ClassicDescSearch(    // search along whisker for best profile match
    double&      x,        // io: (in: old posn of landmark, out: new posn)
    double&      y,        // io:
    const Image& img,      // in: the image scaled to this pyramid level
    const Shape& inshape,  // in: current posn of landmarks (for whisker directions)
    int          ipoint,   // in: index of the current landmark
    const MAT&   meanprof, // in: mean of the training profiles for this point
    const MAT&   covi)     // in: inverse of the covar of the training profiles
{
    const int proflen = NSIZE(meanprof);
    CV_Assert(proflen % 2 == 1); // proflen must be odd in this implementation

    // fullprof is the 1D profile along the whisker including the extra
    // elements to allow search +-CLASSIC_MAX_OFFSET pixels away from
    // the current position of the landmark.
    // We precalculate the fullprof for efficiency in the for loop below.

    const int fullproflen = proflen + 2 * CLASSIC_MAX_OFFSET;
    CV_Assert(fullproflen % 2 == 1); // fullprof length must be odd
    const VEC fullprof(FullProf(img, inshape, ipoint, fullproflen));

    // move along the whisker looking for the best match

    int bestoffset = 0;
    double mindist = FLT_MAX;
    for (int offset = -CLASSIC_MAX_OFFSET;
             offset <= CLASSIC_MAX_OFFSET;
             offset += CLASSIC_SEARCH_RESOL)
    {
        // Get the profile distance.  That is,  get the image profile at the given
        // offset along the whisker, and return the Mahalanobis distance between
        // it and the model mean profile.  Low distance means good fit.

        const VEC prof(SubProf(offset, proflen, fullprof));

        // The following code is equivalent to
        //      dist = (prof - meanprof).t() * covi * (prof - meanprof)
        // but is optimized for speed.

        prof -= meanprof;      // for efficiency, use "-=" not "=" with "-"
        const double dist = xAx(prof, covi);

        if (dist < mindist)
        {
            mindist = dist;
            bestoffset = offset;
        }
    }
    // change x,y to the best position along the whisker

    double xstep, ystep;
    WhiskerStep(xstep, ystep, inshape, ipoint);
    x = inshape(ipoint, IX) + (bestoffset * xstep);
    y = inshape(ipoint, IY) + (bestoffset * ystep);
}

} // namespace stasm