core/vgl/vgl_homg_point_2d.txx

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// This is core/vgl/vgl_homg_point_2d.txx
#ifndef vgl_homg_point_2d_txx_
#define vgl_homg_point_2d_txx_

#include "vgl_homg_point_2d.h"
#include <vgl/vgl_homg_line_2d.h>
#include <vcl_iostream.h>

// Note that the given lines must be distinct!
template <class Type>
vgl_homg_point_2d<Type>::vgl_homg_point_2d (vgl_homg_line_2d<Type> const& l1,
                                            vgl_homg_line_2d<Type> const& l2)
{
  set(l1.b()*l2.c()-l1.c()*l2.b(),
      l1.c()*l2.a()-l1.a()*l2.c(),
      l1.a()*l2.b()-l1.b()*l2.a());
}

template <class T>
double cross_ratio(vgl_homg_point_2d<T>const& p1, vgl_homg_point_2d<T>const& p2,
                   vgl_homg_point_2d<T>const& p3, vgl_homg_point_2d<T>const& p4)
{
  // least squares solution: (Num_x-CR*Den_x)^2 + (Num_y-CR*Den_y)^2 minimal.
  double Num_x = (p1.x()*p3.w()-p3.x()*p1.w())*(p2.x()*p4.w()-p4.x()*p2.w());
  double Num_y = (p1.y()*p3.w()-p3.y()*p1.w())*(p2.y()*p4.w()-p4.y()*p2.w());
  double Den_x = (p1.x()*p4.w()-p4.x()*p1.w())*(p2.x()*p3.w()-p3.x()*p2.w());
  double Den_y = (p1.y()*p4.w()-p4.y()*p1.w())*(p2.y()*p3.w()-p3.y()*p2.w());
  if (Den_x == Den_y) return 0.5*(Num_x+Num_y)/Den_x;
  else return (Den_x*Num_x+Den_y*Num_y)/(Den_x*Den_x+Den_y*Den_y);
}

template <class Type>
vcl_ostream& operator<<(vcl_ostream& s, vgl_homg_point_2d<Type> const& p)
{
  return s << " <vgl_homg_point_2d ("
           << p.x() << ',' << p.y() << ',' << p.w() << ") >";
}

template <class Type>
vcl_istream& operator>>(vcl_istream& s, vgl_homg_point_2d<Type>& p)
{
  Type x, y, w;
  s >> x >> y >> w;
  p.set(x,y,w);
  return s;
}

#undef VGL_HOMG_POINT_2D_INSTANTIATE
#define VGL_HOMG_POINT_2D_INSTANTIATE(T) \
template class vgl_homg_point_2d<T >; \
template double cross_ratio(vgl_homg_point_2d<T >const&, vgl_homg_point_2d<T >const&, \
                            vgl_homg_point_2d<T >const&, vgl_homg_point_2d<T >const&); \
template vcl_ostream& operator<<(vcl_ostream&, vgl_homg_point_2d<T >const&); \
template vcl_istream& operator>>(vcl_istream&, vgl_homg_point_2d<T >&)

#endif // vgl_homg_point_2d_txx_