#ifndef header3d_h
  #define header3d_h
  
#define pt3(X,Y,Z) ((point3d_t){X,Y,Z})

  typedef struct point3d_s {
    double x, y, z;
  } point3d_t;

  void Init3d      (point3d_t *this) ;
  void Scale3d     (point3d_t *this, point3d_t that) ;
  void Rotate3d    (point3d_t *this, point3d_t that) ;
  void Translate3d (point3d_t *this, point3d_t that) ;

#endif