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/**
*
* Get two grid locators and compute the great-circle distance
* between the centers of the two corresponding squares
*
*
* Usage: gridcal <grid1> [<grid2> [<pwr>]]
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <string.h>
#include <ctype.h>
#define MIN(a,b) ((a)>(b)?(b):(a))
#define R 6371
#ifndef M_PI
#define M_PI 3.14159265358979323846 /* pi */
#endif
#ifndef M_PI_2
#define M_PI_2 1.57079632679489661923 /* pi/2 */
#endif
typedef struct {
double lat;
double lon;
} latlon_t;
void usage(char *argv0){
printf("Usage: %s <loc1> [<loc2> [<pwr>]]", argv0);
exit(1);
}
int check_input(char *s){
int S = strlen(s);
#ifdef __DEBUG__
fprintf(stderr, "locator: %s (length: %d)\n", s, S);
#endif
if (S>6 || S<4 || S%2 == 1
|| tolower(s[0]) < 'a' || tolower(s[0]) > 'r'
|| tolower(s[1]) < 'a' || tolower(s[1]) > 'r'
|| s[2] < '0' || s[2] > '9'
|| s[3] < '0' || s[3] > '9'
|| (S > 4 && (tolower(s[4]) < 'a' || tolower(s[4]) > 'x'
|| tolower(s[5]) < 'a' || tolower(s[5]) > 'x'))) {
printf("Invalid locator: %s\n", s);
exit(1);
}
}
/**
*
* This function takes a valid locator and returns the coordinates
* of the centre of the corresponding square in the latlon_t structure
*
*/
void grid_to_latlon(char *s, latlon_t *c){
c->lat = c->lon = 0;
/* longitude first */
c->lon += (tolower(s[0])-'a')*20.0 - 180;
c->lon += (s[2]-'0')*2.0;
/* we always consider the centre of the square, not the corner...*/
if (strlen(s)>4){
c->lon += (tolower(s[4]) - 'a') * 1.0/12 + 1.0/24;
}
else {
c->lon += 1.0;
}
/* then latitude */
c->lat += (tolower(s[1])-'a')*10.0 - 90;
c->lat += (s[3]-'0')*1.0;
/* we always consider the centre of the square, not the corner...*/
if (strlen(s)>4){
c->lat += (tolower(s[5]) - 'a') * 1.0/24 + 1.0/48;
}
else {
c->lat += 0.5;
}
c->lon = c->lon/180 * M_PI;
c->lat = c->lat/90 * M_PI_2;
}
double heversine_dist(latlon_t *c1, latlon_t *c2){
double d=0.0, d1=0, d2=0;
d1 = sin(0.5*(c2->lat - c1->lat));
d1 = d1 * d1;
d2 = sin(0.5*(c2->lon - c1->lon));
d2 = d2 * d2;
d2 = d2 * cos(c1->lat) * cos(c2->lat);
d = 2 * R * asin(sqrt(d1 + d2));
return d;
}
int main(int argc, char *argv[]){
char loc1[7], loc2[7];
int n1, n2;
latlon_t c1, c2;
double d;
double pwr;
if (argc < 2){
usage(argv[0]);
}
if (argc == 2){
/* We only convert a grid locator to lat-long */
n1=MIN(strlen(argv[1]),6);
strncpy(loc1, argv[1], n1);
loc1[n1] = '\0';
check_input(loc1);
grid_to_latlon(loc1, &c1);
printf("%s %g %g %g %g\n", loc1, c1.lat*180/M_PI, c1.lon*180/M_PI, c1.lat, c1.lon);
exit(0);
}
n1=MIN(strlen(argv[1]),6);
n2=MIN(strlen(argv[2]),6);
strncpy(loc1, argv[1], n1);
strncpy(loc2, argv[2], n2);
loc1[n1] = '\0';
loc2[n2] = '\0';
check_input(loc1);
check_input(loc2);
grid_to_latlon(loc1, &c1);
grid_to_latlon(loc2, &c2);
d = heversine_dist(&c1, &c2);
if (argc > 3){
pwr = atof(argv[3]);
printf("%s %s %g %g %g %g %g\n", \
loc1, loc2, d, d/1.60934, pwr, d/pwr, d/(1.60934*pwr));
}
else {
printf("%s %s %g %g\n", loc1, loc2, d, d/1.60934);
}
}
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