openpilot is an open source driver assistance system. openpilot performs the functions of Automated Lane Centering and Adaptive Cruise Control for over 200 supported car makes and models.
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#include <iostream>
#include <cmath>
#include <Eigen/Dense>
#include "data.h"
Eigen::Matrix<float, MODEL_PATH_DISTANCE, POLYFIT_DEGREE> vander;
void poly_init(){
// Build Vandermonde matrix
for(int i = 0; i < MODEL_PATH_DISTANCE; i++) {
for(int j = 0; j < POLYFIT_DEGREE; j++) {
vander(i, j) = pow(i, POLYFIT_DEGREE-j-1);
}
}
}
void poly_fit(float *in_pts, float *in_stds, float *out) {
// References to inputs
Eigen::Map<Eigen::Matrix<float, MODEL_PATH_DISTANCE, 1> > pts(in_pts, MODEL_PATH_DISTANCE);
Eigen::Map<Eigen::Matrix<float, MODEL_PATH_DISTANCE, 1> > std(in_stds, MODEL_PATH_DISTANCE);
Eigen::Map<Eigen::Matrix<float, POLYFIT_DEGREE, 1> > p(out, POLYFIT_DEGREE);
// Build Least Squares equations
Eigen::Matrix<float, MODEL_PATH_DISTANCE, POLYFIT_DEGREE> lhs = vander.array().colwise() / std.array();
Eigen::Matrix<float, MODEL_PATH_DISTANCE, 1> rhs = pts.array() / std.array();
Eigen::Matrix<float, POLYFIT_DEGREE, 1> scale = 1. / (lhs.array()*lhs.array()).sqrt().colwise().sum();
lhs = lhs * scale.asDiagonal();
// Solve inplace
Eigen::ColPivHouseholderQR<Eigen::Ref<Eigen::MatrixXf> > qr(lhs);
p = qr.solve(rhs);
p = p.transpose() * scale.asDiagonal();
}
int main(void) {
poly_init();
float poly[4];
poly_fit(pts, stds, poly);
std::cout << "[";
std::cout << poly[0] << ",";
std::cout << poly[1] << ",";
std::cout << poly[2] << ",";
std::cout << poly[3];
std::cout << "]" << std::endl;
}