Spline.h

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// This file is part of Eigen, a lightweight C++ template library
// for linear algebra.
//
// Copyright (C) 20010-2011 Hauke Heibel <hauke.heibel@gmail.com>
//
// This Source Code Form is subject to the terms of the Mozilla
// Public License v. 2.0. If a copy of the MPL was not distributed
// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
#ifndef EIGEN_SPLINE_H
#define EIGEN_SPLINE_H
 
#include "./InternalHeaderCheck.h"
 
#include "SplineFwd.h"
 
namespace Eigen
{
  template <typename Scalar_, int Dim_, int Degree_>
  class Spline
  {
  public:
    typedef Scalar_ Scalar; 
    enum { Dimension = Dim_  };
    enum { Degree = Degree_  };
 
    typedef typename SplineTraits<Spline>::PointType PointType;
    
    typedef typename SplineTraits<Spline>::KnotVectorType KnotVectorType;
 
    typedef typename SplineTraits<Spline>::ParameterVectorType ParameterVectorType;
    
    typedef typename SplineTraits<Spline>::BasisVectorType BasisVectorType;
 
    typedef typename SplineTraits<Spline>::BasisDerivativeType BasisDerivativeType;
    
    typedef typename SplineTraits<Spline>::ControlPointVectorType ControlPointVectorType;
    
    Spline() 
    : m_knots(1, (Degree==Dynamic ? 2 : 2*Degree+2))
    , m_ctrls(ControlPointVectorType::Zero(Dimension,(Degree==Dynamic ? 1 : Degree+1))) 
    {
      // in theory this code can go to the initializer list but it will get pretty
      // much unreadable ...
      enum { MinDegree = (Degree==Dynamic ? 0 : Degree) };
      m_knots.template segment<MinDegree+1>(0) = Array<Scalar,1,MinDegree+1>::Zero();
      m_knots.template segment<MinDegree+1>(MinDegree+1) = Array<Scalar,1,MinDegree+1>::Ones();
    }
 
    template <typename OtherVectorType, typename OtherArrayType>
    Spline(const OtherVectorType& knots, const OtherArrayType& ctrls) : m_knots(knots), m_ctrls(ctrls) {}
 
    template <int OtherDegree>
    Spline(const Spline<Scalar, Dimension, OtherDegree>& spline) : 
    m_knots(spline.knots()), m_ctrls(spline.ctrls()) {}
 
    const KnotVectorType& knots() const { return m_knots; }
    
    const ControlPointVectorType& ctrls() const { return m_ctrls; }
 
    PointType operator()(Scalar u) const;
 
    typename SplineTraits<Spline>::DerivativeType
      derivatives(Scalar u, DenseIndex order) const;
 
    template <int DerivativeOrder>
    typename SplineTraits<Spline,DerivativeOrder>::DerivativeType
      derivatives(Scalar u, DenseIndex order = DerivativeOrder) const;
 
    typename SplineTraits<Spline>::BasisVectorType
      basisFunctions(Scalar u) const;
 
    typename SplineTraits<Spline>::BasisDerivativeType
      basisFunctionDerivatives(Scalar u, DenseIndex order) const;
 
    template <int DerivativeOrder>
    typename SplineTraits<Spline,DerivativeOrder>::BasisDerivativeType
      basisFunctionDerivatives(Scalar u, DenseIndex order = DerivativeOrder) const;
 
    DenseIndex degree() const;
 
    DenseIndex span(Scalar u) const;
 
    static DenseIndex Span(typename SplineTraits<Spline>::Scalar u, DenseIndex degree, const typename SplineTraits<Spline>::KnotVectorType& knots);
    
    static BasisVectorType BasisFunctions(Scalar u, DenseIndex degree, const KnotVectorType& knots);
 
    static BasisDerivativeType BasisFunctionDerivatives(
      const Scalar u, const DenseIndex order, const DenseIndex degree, const KnotVectorType& knots);
 
  private:
    KnotVectorType m_knots; 
    ControlPointVectorType  m_ctrls; 
    template <typename DerivativeType>
    static void BasisFunctionDerivativesImpl(
      const typename Spline<Scalar_, Dim_, Degree_>::Scalar u,
      const DenseIndex order,
      const DenseIndex p,
      const typename Spline<Scalar_, Dim_, Degree_>::KnotVectorType& U,
      DerivativeType& N_);
  };
 
  template <typename Scalar_, int Dim_, int Degree_>
  DenseIndex Spline<Scalar_, Dim_, Degree_>::Span(
    typename SplineTraits< Spline<Scalar_, Dim_, Degree_> >::Scalar u,
    DenseIndex degree,
    const typename SplineTraits< Spline<Scalar_, Dim_, Degree_> >::KnotVectorType& knots)
  {
    // Piegl & Tiller, "The NURBS Book", A2.1 (p. 68)
    if (u <= knots(0)) return degree;
    const Scalar* pos = std::upper_bound(knots.data()+degree-1, knots.data()+knots.size()-degree-1, u);
    return static_cast<DenseIndex>( std::distance(knots.data(), pos) - 1 );
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  typename Spline<Scalar_, Dim_, Degree_>::BasisVectorType
    Spline<Scalar_, Dim_, Degree_>::BasisFunctions(
    typename Spline<Scalar_, Dim_, Degree_>::Scalar u,
    DenseIndex degree,
    const typename Spline<Scalar_, Dim_, Degree_>::KnotVectorType& knots)
  {
    const DenseIndex p = degree;
    const DenseIndex i = Spline::Span(u, degree, knots);
 
    const KnotVectorType& U = knots;
 
    BasisVectorType left(p+1); left(0) = Scalar(0);
    BasisVectorType right(p+1); right(0) = Scalar(0);
 
    VectorBlock<BasisVectorType,Degree>(left,1,p) = u - VectorBlock<const KnotVectorType,Degree>(U,i+1-p,p).reverse();
    VectorBlock<BasisVectorType,Degree>(right,1,p) = VectorBlock<const KnotVectorType,Degree>(U,i+1,p) - u;
 
    BasisVectorType N(1,p+1);
    N(0) = Scalar(1);
    for (DenseIndex j=1; j<=p; ++j)
    {
      Scalar saved = Scalar(0);
      for (DenseIndex r=0; r<j; r++)
      {
        const Scalar tmp = N(r)/(right(r+1)+left(j-r));
        N[r] = saved + right(r+1)*tmp;
        saved = left(j-r)*tmp;
      }
      N(j) = saved;
    }
    return N;
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  DenseIndex Spline<Scalar_, Dim_, Degree_>::degree() const
  {
    if (Degree_ == Dynamic)
      return m_knots.size() - m_ctrls.cols() - 1;
    else
      return Degree_;
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  DenseIndex Spline<Scalar_, Dim_, Degree_>::span(Scalar u) const
  {
    return Spline::Span(u, degree(), knots());
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  typename Spline<Scalar_, Dim_, Degree_>::PointType Spline<Scalar_, Dim_, Degree_>::operator()(Scalar u) const
  {
    enum { Order = SplineTraits<Spline>::OrderAtCompileTime };
 
    const DenseIndex span = this->span(u);
    const DenseIndex p = degree();
    const BasisVectorType basis_funcs = basisFunctions(u);
 
    const Replicate<BasisVectorType,Dimension,1> ctrl_weights(basis_funcs);
    const Block<const ControlPointVectorType,Dimension,Order> ctrl_pts(ctrls(),0,span-p,Dimension,p+1);
    return (ctrl_weights * ctrl_pts).rowwise().sum();
  }
 
  /* --------------------------------------------------------------------------------------------- */
 
  template <typename SplineType, typename DerivativeType>
  void derivativesImpl(const SplineType& spline, typename SplineType::Scalar u, DenseIndex order, DerivativeType& der)
  {    
    enum { Dimension = SplineTraits<SplineType>::Dimension };
    enum { Order = SplineTraits<SplineType>::OrderAtCompileTime };
    enum { DerivativeOrder = DerivativeType::ColsAtCompileTime };
 
    typedef typename SplineTraits<SplineType>::ControlPointVectorType ControlPointVectorType;
    typedef typename SplineTraits<SplineType,DerivativeOrder>::BasisDerivativeType BasisDerivativeType;
    typedef typename BasisDerivativeType::ConstRowXpr BasisDerivativeRowXpr;    
 
    const DenseIndex p = spline.degree();
    const DenseIndex span = spline.span(u);
 
    const DenseIndex n = (std::min)(p, order);
 
    der.resize(Dimension,n+1);
 
    // Retrieve the basis function derivatives up to the desired order...    
    const BasisDerivativeType basis_func_ders = spline.template basisFunctionDerivatives<DerivativeOrder>(u, n+1);
 
    // ... and perform the linear combinations of the control points.
    for (DenseIndex der_order=0; der_order<n+1; ++der_order)
    {
      const Replicate<BasisDerivativeRowXpr,Dimension,1> ctrl_weights( basis_func_ders.row(der_order) );
      const Block<const ControlPointVectorType,Dimension,Order> ctrl_pts(spline.ctrls(),0,span-p,Dimension,p+1);
      der.col(der_order) = (ctrl_weights * ctrl_pts).rowwise().sum();
    }
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  typename SplineTraits< Spline<Scalar_, Dim_, Degree_> >::DerivativeType
    Spline<Scalar_, Dim_, Degree_>::derivatives(Scalar u, DenseIndex order) const
  {
    typename SplineTraits< Spline >::DerivativeType res;
    derivativesImpl(*this, u, order, res);
    return res;
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  template <int DerivativeOrder>
  typename SplineTraits< Spline<Scalar_, Dim_, Degree_>, DerivativeOrder >::DerivativeType
    Spline<Scalar_, Dim_, Degree_>::derivatives(Scalar u, DenseIndex order) const
  {
    typename SplineTraits< Spline, DerivativeOrder >::DerivativeType res;
    derivativesImpl(*this, u, order, res);
    return res;
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  typename SplineTraits< Spline<Scalar_, Dim_, Degree_> >::BasisVectorType
    Spline<Scalar_, Dim_, Degree_>::basisFunctions(Scalar u) const
  {
    return Spline::BasisFunctions(u, degree(), knots());
  }
 
  /* --------------------------------------------------------------------------------------------- */
  
  
  template <typename Scalar_, int Dim_, int Degree_>
  template <typename DerivativeType>
  void Spline<Scalar_, Dim_, Degree_>::BasisFunctionDerivativesImpl(
    const typename Spline<Scalar_, Dim_, Degree_>::Scalar u,
    const DenseIndex order,
    const DenseIndex p, 
    const typename Spline<Scalar_, Dim_, Degree_>::KnotVectorType& U,
    DerivativeType& N_)
  {
    typedef Spline<Scalar_, Dim_, Degree_> SplineType;
    enum { Order = SplineTraits<SplineType>::OrderAtCompileTime };
 
    const DenseIndex span = SplineType::Span(u, p, U);
 
    const DenseIndex n = (std::min)(p, order);
 
    N_.resize(n+1, p+1);
 
    BasisVectorType left = BasisVectorType::Zero(p+1);
    BasisVectorType right = BasisVectorType::Zero(p+1);
 
    Matrix<Scalar,Order,Order> ndu(p+1,p+1);
 
    Scalar saved, temp; // FIXME These were double instead of Scalar. Was there a reason for that?
 
    ndu(0,0) = 1.0;
 
    DenseIndex j;
    for (j=1; j<=p; ++j)
    {
      left[j] = u-U[span+1-j];
      right[j] = U[span+j]-u;
      saved = 0.0;
 
      for (DenseIndex r=0; r<j; ++r)
      {
        /* Lower triangle */
        ndu(j,r) = right[r+1]+left[j-r];
        temp = ndu(r,j-1)/ndu(j,r);
        /* Upper triangle */
        ndu(r,j) = static_cast<Scalar>(saved+right[r+1] * temp);
        saved = left[j-r] * temp;
      }
 
      ndu(j,j) = static_cast<Scalar>(saved);
    }
 
    for (j = p; j>=0; --j) 
      N_(0,j) = ndu(j,p);
 
    // Compute the derivatives
    DerivativeType a(n+1,p+1);
    DenseIndex r=0;
    for (; r<=p; ++r)
    {
      DenseIndex s1,s2;
      s1 = 0; s2 = 1; // alternate rows in array a
      a(0,0) = 1.0;
 
      // Compute the k-th derivative
      for (DenseIndex k=1; k<=static_cast<DenseIndex>(n); ++k)
      {
        Scalar d = 0.0;
        DenseIndex rk,pk,j1,j2;
        rk = r-k; pk = p-k;
 
        if (r>=k)
        {
          a(s2,0) = a(s1,0)/ndu(pk+1,rk);
          d = a(s2,0)*ndu(rk,pk);
        }
 
        if (rk>=-1) j1 = 1;
        else        j1 = -rk;
 
        if (r-1 <= pk) j2 = k-1;
        else           j2 = p-r;
 
        for (j=j1; j<=j2; ++j)
        {
          a(s2,j) = (a(s1,j)-a(s1,j-1))/ndu(pk+1,rk+j);
          d += a(s2,j)*ndu(rk+j,pk);
        }
 
        if (r<=pk)
        {
          a(s2,k) = -a(s1,k-1)/ndu(pk+1,r);
          d += a(s2,k)*ndu(r,pk);
        }
 
        N_(k,r) = static_cast<Scalar>(d);
        j = s1; s1 = s2; s2 = j; // Switch rows
      }
    }
 
    /* Multiply through by the correct factors */
    /* (Eq. [2.9])                             */
    r = p;
    for (DenseIndex k=1; k<=static_cast<DenseIndex>(n); ++k)
    {
      for (j=p; j>=0; --j) N_(k,j) *= r;
      r *= p-k;
    }
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  typename SplineTraits< Spline<Scalar_, Dim_, Degree_> >::BasisDerivativeType
    Spline<Scalar_, Dim_, Degree_>::basisFunctionDerivatives(Scalar u, DenseIndex order) const
  {
    typename SplineTraits<Spline<Scalar_, Dim_, Degree_> >::BasisDerivativeType der;
    BasisFunctionDerivativesImpl(u, order, degree(), knots(), der);
    return der;
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  template <int DerivativeOrder>
  typename SplineTraits< Spline<Scalar_, Dim_, Degree_>, DerivativeOrder >::BasisDerivativeType
    Spline<Scalar_, Dim_, Degree_>::basisFunctionDerivatives(Scalar u, DenseIndex order) const
  {
    typename SplineTraits< Spline<Scalar_, Dim_, Degree_>, DerivativeOrder >::BasisDerivativeType der;
    BasisFunctionDerivativesImpl(u, order, degree(), knots(), der);
    return der;
  }
 
  template <typename Scalar_, int Dim_, int Degree_>
  typename SplineTraits<Spline<Scalar_, Dim_, Degree_> >::BasisDerivativeType
  Spline<Scalar_, Dim_, Degree_>::BasisFunctionDerivatives(
    const typename Spline<Scalar_, Dim_, Degree_>::Scalar u,
    const DenseIndex order,
    const DenseIndex degree,
    const typename Spline<Scalar_, Dim_, Degree_>::KnotVectorType& knots)
  {
    typename SplineTraits<Spline>::BasisDerivativeType der;
    BasisFunctionDerivativesImpl(u, order, degree, knots, der);
    return der;
  }
}
 
#endif // EIGEN_SPLINE_H