void fitLine(float &x, float &xSlope, float &xQuality, const int &ipl1, const int &nclus1, const std::vector< int > &xclus1, const std::vector< int > &wclus1, const int &ipl2, const int &nclus2, const std::vector< int > &xclus2, const std::vector< int > &wclus2) const