text: #include <stdio.h>
  #include <stdlib.h>
  #include <math.h>
  
  #include "lfa.h"
  
  /* Vector must be in (-h, delta) system, and not adjusted for refraction. */
  
  double v_parallactic (double sinphi, double cosphi, double v[3]) {
    return atan2(v[1] * sinphi, (1.0 - v[2]*v[2]) * sinphi - v[0]*v[2] * cosphi);
  }
  