PixelTrackFitting/interface/CircleFromThreePoints.h

0001 #ifndef RecoTracker_PixelTrackFitting_CircleFromThreePoints_h
0002 #define RecoTracker_PixelTrackFitting_CircleFromThreePoints_h
0003
0004 #include "DataFormats/GeometryVector/interface/GlobalPoint.h"
0005 #include "DataFormats/GeometryVector/interface/Basic2DVector.h"
0006
0007 /** Computes the curvature (1/radius) and, if possible, the center
0008  *  of the circle passing through three points.
0009  *  The input points are three dimensional for convenience, but the
0010  *  calculation is done in the transverse (x,y) plane.
0011  *  No verification of the reasonableness of the z coordinate is done.
0012  *  If the three points lie on a line the curvature is zero and the center
0013  *  position is undefined. The 3 points are assumed to make sense:
0014  *  if the distance between two of them is very small compared to
0015  *  the ditance to the third the result will be numerically unstable.
0016  */
0017
0018 class CircleFromThreePoints {
0019 public:
0020   /// dummy
0021   CircleFromThreePoints() {}
0022
0023   typedef Basic2DVector<float> Vector2D;
0024
0025   /** Construct from three points (see class description).
0026    *  The order of points is not essential, but accuracy should be better if
0027    *  the second point lies between the other two on the circle.
0028    *  The optional argument "precision" specifies how accurately the
0029    *  straight line check has to be satisfied for setting the curvature
0030    *  to zero and the center position to "undefined".
0031    */
0032   CircleFromThreePoints(const GlobalPoint& inner,
0033                         const GlobalPoint& mid,
0034                         const GlobalPoint& outer,
0035                         double precision = 1.e-7);
0036
0037   /** Returns the curvature (1/radius), in cm^(-1).
0038    *  The curvature is precomputed, this is just access method (takes no time).
0039    *  If curvature is zero the center is undefined
0040    *  (see description of presicion above).
0041    */
0042   float curvature() const { return theCurvature; }
0043
0044   /** returns the position of the center of the circle.
0045    *  If curvature is zero, center() throws an exception to avoid use of
0046    *  undefined position.
0047    *  If the curvature is very small the position of the center will
0048    *  be very inaccurate.
0049    */
0050   Vector2D center() const { return theCenter; }
0051
0052 private:
0053   float theCurvature;
0054   Vector2D theCenter;
0055
0056   void init(const Vector2D& b, const Vector2D& c, const Vector2D& offset, double precision);
0057 };
0058
0059 #endif  // RecoTracker_PixelTrackFitting_CircleFromThreePoints_h