CircleFromThreePoints.cc

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#include "RecoTracker/PixelTrackFitting/interface/CircleFromThreePoints.h"

CircleFromThreePoints::CircleFromThreePoints(const GlobalPoint& inner,
                                             const GlobalPoint& mid,
                                             const GlobalPoint& outer,
                                             double precision) {
  // move to frame where inner.x() == inner.y() == 0;
  Vector2D b(mid.x() - inner.x(), mid.y() - inner.y());
  Vector2D c(outer.x() - inner.x(), outer.y() - inner.y());
  init(b, c, Vector2D(inner.x(), inner.y()), precision);
}

void CircleFromThreePoints::init(const Vector2D& b, const Vector2D& c, const Vector2D& offset, double precision) {
  double b2 = b.mag2();
  double c2 = c.mag2();

  double oX(0), oY(0);
  bool solved = false;
  if (fabs(b.x()) > fabs(b.y())) {  // solve for y first
    double k = c.x() / b.x();
    double div = 2 * (k * b.y() - c.y());
    if (fabs(div) < precision)
      theCurvature = 0;  // if the 3 points lie on a line
    else {
      oY = (k * b2 - c2) / div;
      oX = b2 / (2 * b.x()) - b.y() / b.x() * oY;
      solved = true;
    }
  } else {  // solve for x first
    double k = c.y() / b.y();
    double div = 2 * (k * b.x() - c.x());
    if (fabs(div) < precision)
      theCurvature = 0;  // if the 3 points lie on a line
    else {
      oX = (k * b2 - c2) / div;
      oY = b2 / (2 * b.y()) - b.x() / b.y() * oX;
      solved = true;
    }
  }
  if (solved) {
    theCurvature = 1. / sqrt(oX * oX + oY * oY);
    double xC = oX + offset.x();
    double yC = oY + offset.y();
    theCenter = Vector2D(xC, yC);
    //    thePhi = acos(xC/sqrt(xC*xC + yC*yC));

    //    if (xC<0.) thePhi = thePhi - PI;
    //    cout << setiosflags(ios::showpoint | ios::fixed);
    //
    //    cout << "CircleFromThreePoints::init curv = " << theCurvature << endl;
    //    cout << "CircleFromThreePoints::init center prime = " << oX << " " << oY << endl;
    //    cout << "CircleFromThreePoints::init offset = " << offset.x() << " " << offset.y() << endl;
    //    cout << "CircleFromThreePoints::init center = " << theCenter.x()<< " " << theCenter.y() << endl;
    //
    //    float d = sqrt(theCenter.x()*theCenter.x()+theCenter.y()*theCenter.y());
    //    cout << "CircleFromThreePoints::init dfloat = " << setw(10) << setprecision(5) << d << endl;
    //    cout << "CircleFromThreePoints::init radius = " << 1/theCurvature << endl;
  }
}