day 6 assignment

/* This program determines the distance between two points */

/* that are specified with latitude and longitude values */

/* that are in the Northern Hemisphere. */

#include <stdio.h>

#include <math.h>

#define PI 3.141593

int main(void)

{

/* Declare variables and function prototype. */

double lat1, long1, lat2, long2;

double gc_distance(double lat1,double long1,

double lat2,double long2);

/* Get locations of two points. */

printf("Enter latitude north and longitude west ");

printf("for location 1: \n");

scanf("%lf %lf",&lat1,&long1);

printf("Enter latitude north and longitude west ");

printf("for location 2: \n");

scanf("%lf %lf",&lat2,&long2);

/* Print great circle distance. */

printf("Great Circle Distance: %.0f miles \n",

gc_distance(lat1,long1,lat2,long2));

/* Exit program. */

return 0;

}

//////////////////////////////////////////////

/* This function computes the distance between two */

/* points using great circle distances. */

double gc_distance(double lat1,double long1,

double lat2,double long2)

{

/* Declare variables. */

double rho, phi, theta, gamma, dot, dist1, dist2,x1, y1, z1, x2, y2, z2;

/* Convert latitude,longitude to rectangular coordinates. */

rho = 3960;

phi = (90 - lat1)*(PI/180.0);

theta = (360 - long1)*(PI/180.0);

x1 = rho*sin(phi)*cos(theta);

y1 = rho*sin(phi)*sin(theta);

z1 = rho*cos(phi);

phi = (90 - lat2)*(PI/180.0);

theta = (360 - long2)*(PI/180.0);

x2 = rho*sin(phi)*cos(theta);

y2 = rho*sin(phi)*sin(theta);

z2 = rho*cos(phi);

/* Compute angle between vectors. */

dot = x1*x2 + y1*y2 + z1*z2;

dist1 = sqrt(x1*x1 + y1*y1 + z1*z1);

dist2 = sqrt(x2*x2 + y2*y2 + z2*z2);

gamma = acos(dot/(dist1*dist2));

/* Compute and return great circle distance. */

return gamma*rho;

}