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Moon Distance

sarker306 Sep 18th, 2019 (edited) 85 Never
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  1. #include <stdio.h>
  2. #include <math.h>
  3.  
  4. const double pi = 2*acos(0);
  5. const double R = 6371; /* the radius of earth in km */
  6.  
  7. /* given latitudes on same longitudes and zenith angles, get the distance of the moon.
  8.    only works when latitudes are on different hemispheres.
  9.    latitude on southern hemisphere is negative */
  10. double get_moon_distance(double lat1, double lat2, double zen1, double zen2);
  11.  
  12. int main(){
  13.     double lat1, lat2, zen1, zen2;
  14.  
  15.     while (scanf("%lf%lf%lf%lf", &lat1, &lat2, &zen1, &zen2) != EOF ){
  16.         printf("%lf\n", get_moon_distance(lat1, lat2, zen1, zen2));
  17.     }
  18.  
  19.     return 0;
  20. }
  21.  
  22. double get_moon_distance(double lat1, double lat2, double zen1, double zen2) {
  23.     double tmp;
  24.     double lin_dist;
  25.     double ang_dist;
  26.     double lunar_angle_between_points;
  27.     double moon_dist_from_center;
  28.     double moon_dist_from_upper_point;
  29.  
  30.     /* make sure lat1 > lat2 */
  31.     if ( lat1 < lat2 ) {
  32.         tmp = lat1; lat1 = lat2; lat2 = tmp;
  33.         tmp = zen1; zen1 = zen2; zen2 = tmp;
  34.     }
  35.  
  36.     /* convert angles into radian */
  37.     lat1 *= pi / 180.; lat2 *= pi / 180.; zen1 *= pi / 180.; zen2 *= pi / 180.;
  38.  
  39.     ang_dist = lat1 - lat2;
  40.     lin_dist = R * sin(ang_dist) / cos(ang_dist/2);
  41.     lunar_angle_between_points = zen1 + zen2 - ang_dist;
  42.     moon_dist_from_upper_point = lin_dist * cos(- zen2 + ang_dist/2) / sin(lunar_angle_between_points);
  43.     tmp = R / moon_dist_from_upper_point;
  44.     moon_dist_from_center = moon_dist_from_upper_point * sqrt(1 + tmp * tmp + 2 * tmp * cos(zen1));
  45.     return moon_dist_from_center - R;
  46. }
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