geodesic_constants_and_simple_functions.h

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//Copyright (C) 2008 Danil Kirsanov, MIT License
#ifndef GEODESIC_CONSTANTS_20071231
#define GEODESIC_CONSTANTS_20071231
 
// some constants and simple math functions
 
#include <assert.h>
#include <math.h>
#include <limits>
#include <fstream>
 
namespace geodesic{
 
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
 
//double const GEODESIC_INF = std::numeric_limits<double>::max();
double const GEODESIC_INF = 1e100;
 
//in order to avoid numerical problems with "infinitely small" intervals,
//we drop all the intervals smaller than SMALLEST_INTERVAL_RATIO*edge_length
double const SMALLEST_INTERVAL_RATIO = 1e-6;
//double const SMALL_EPSILON = 1e-10;
 
 
inline double cos_from_edges(double const a,      //compute the cosine of the angle given the lengths of the edges
               double const b,
               double const c)
{
//  assert(a>1e-50);
//  assert(b>1e-50);
//  assert(c>1e-50);
 
  double result = (b*b + c*c - a*a)/(2.0*b*c);
  result = std::max(result, -1.0);
  return std::min(result, 1.0);
}
 
inline double angle_from_edges(double const a,      //compute the cosine of the angle given the lengths of the edges
                 double const b,
                 double const c)
{
  return acos(cos_from_edges(a,b,c));
}
 
template<class Points, class Faces>
inline bool read_mesh_from_file(char* filename,
                Points& points,
                Faces& faces)
{
  std::ifstream file(filename);
  assert(file.is_open());
  if(!file.is_open()) return false;
 
  unsigned num_points;
  file >> num_points;
  assert(num_points>=3);
 
  unsigned num_faces;
  file >> num_faces;
 
  points.resize(num_points*3);
  for(typename Points::iterator i=points.begin(); i!=points.end(); ++i)
  {
    file >> *i;
  }
 
  faces.resize(num_faces*3);
  for(typename Faces::iterator i=faces.begin(); i!=faces.end(); ++i)
  {
    file >> *i;
  }
  file.close();
 
  return true;
}
 
} //geodesic
 
#endif  //GEODESIC_CONSTANTS_20071231