Spline.h

/******************************************************************************************************
 * (C) 2014 markummitchell@github.com. This file is part of Engauge Digitizer, which is released      *
 * under GNU General Public License version 2 (GPLv2) or (at your option) any later version. See file *
 * LICENSE or go to gnu.org/licenses for details. Distribution requires prior written permission.     *
 ******************************************************************************************************/
 
#include "SplineCoeff.h"
#include "SplinePair.h"
#include <vector>
 
class Spline 
{
 public:
  Spline(const std::vector<double> &t,
         const std::vector<SplinePair> &xy);
 
  virtual ~Spline();
 
  SplinePair findSplinePairForFunctionX (double x,
                                         int numIterations) const;
 
  SplinePair interpolateCoeff (double t) const;
 
  SplinePair interpolateControlPoints (double t) const;
 
  SplinePair p1 (unsigned int i) const;
 
  SplinePair p2 (unsigned int i) const;
 
private:
  Spline();
 
  // Although coefficient interpolation works for successive t values not 1.0 apart, the control point interpolation
  // does not so we check the increments. Note that the starting value is arbitrary. Removing this restriction will
  // mean upgrading the code to allow arbitrary t increments
  void checkTIncrements (const std::vector<double> &t) const;
 
  void computeCoefficientsForIntervals (const std::vector<double> &t,
                                        const std::vector<SplinePair> &xy);
  void computeControlPointsForIntervals ();
 
  // Coefficients a,b,c,d
  std::vector<SplineCoeff> m_elements;
 
  // Input times
  std::vector<double> m_t;
 
  // Input points
  std::vector<SplinePair> m_xy;
 
  // Control points for each interval
  std::vector<SplinePair> m_p1;
  std::vector<SplinePair> m_p2;
};