/**
*
* Compute the grid locator associated to a pair of latitude/longitude
* coordinates, given in degrees
*
*/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

void latlon_to_grid(double lat, double lon, char *loc){
	
	double q;

	q = (int)((lon + 180)/20);
	lon = (q==0? lon: fmod(lon+180, 20));
	loc[0] = 'A' + q;
	q = (int)((lat + 90)/10);
	lat = (q==0? lat: fmod(lat+90, 10));
	loc[1] = 'A' + q;
	q = (int)(lon/2);
	lon = (q==0? lon: fmod(lon, 2));
	loc[2] = '0' + q;
	q = (int)(lat);
	lat = (q==0? lat: lat - q);
	loc[3] = '0' + q;
	q = (int)(lon*12);
	loc[4] = 'A' + q;
	q = (int)(lat*24);
	loc[5] = 'A' + q;
	loc[6] = '\0';
}

void usage(char s[]){
	printf("Usage: get_grid <lat> <lon>\n");
	exit(1);
}

int main (int argc, char *argv[]){
	
	double lat, lon;
	char loc[7];

	if (argc < 3){
		usage(argv[0]);
	}

	lat = atof(argv[1]);
	lon = atof(argv[2]);
	while (lat < -90) lat +=180;
	while (lat > 90) lat -=180;
	while (lon < -180) lon += 360;
	while (lon > 180) lon -= 360;
	//fprintf(stderr, "lat: %g lon: %g\n", lat, lon);
	latlon_to_grid(lat, lon, loc);
	printf("%s\n", loc);

}