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/* CWirc - X-Chat plugin for sending and receiving raw morse code over IRC
(c) Pierre-Philippe Coupard - 18/06/2003
Grid squares distance routines
This program is distributed under the terms of the GNU General Public License
See the COPYING file for details
*/
#include <string.h>
#include <ctype.h>
#include <math.h>
#include "grid.h"
/* Definitions */
#define EARTH_RADIUS 6367 /* km, average */
/* Prototypes */
static void gridsquare_to_latlon(char *gs,double *lat,double *lon);
/* Check if a string is a valid 4- or 6-character grid square */
int cwirc_is_grid_square(char *gs)
{
int i;
/* Test the length of the string */
i=strlen(gs);
if(i!=4 && i!=6)
return(0);
/* Test its format */
if(toupper(gs[0])<'A' || toupper(gs[0])>'R' ||
toupper(gs[1])<'A' || toupper(gs[1])>'R' ||
!isdigit(gs[2]) ||
!isdigit(gs[3]) ||
(i==6 && (toupper(gs[4])<'A' || toupper(gs[4])>'X' ||
toupper(gs[5])<'A' || toupper(gs[5])>'X')))
return(0);
return(1);
}
/* Calculate the great circle path between 2 grid squares' centers in Km */
int cwirc_great_circle_path(char *gs1,char *gs2)
{
double lat1,lon1;
double lat2,lon2;
double a,d;
/* Convert the grid squares to latitude/longitude */
gridsquare_to_latlon(gs1,&lat1,&lon1);
gridsquare_to_latlon(gs2,&lat2,&lon2);
/* Calculate the great circle path */
a=pow(sin((lat2-lat1)/2),2) + cos(lat1)*cos(lat2)*pow(sin((lon2-lon1)/2),2);
d=EARTH_RADIUS * 2*atan2(sqrt(a),sqrt(1-a));
return(d);
}
/* Calculate the latitude/longitude (in rads) of the center of a grid square */
static void gridsquare_to_latlon(char *gs,double *lat,double *lon)
{
/* Calculate the base coordinates of the corner of the grid square */
*lon=-M_PI +(toupper(gs[0])-'A')*((M_PI/180)*20)+(gs[2]-'0')*((M_PI/180)*2);
*lat=-M_PI/2 +(toupper(gs[1])-'A')*((M_PI/180)*10)+(gs[3]-'0')*((M_PI/180)*1);
/* Is it a short (4 character) or long (6 character) grid square ? */
if(strlen(gs)==4)
{
/* Calculate the center of the grid square */
*lon+=(M_PI/180)*1;
*lat+=(M_PI/180)*.5;
}
else
{
/* Increase precision of the coordinates of the corner of the grid square */
*lon+=(toupper(gs[4])-'A')*(((M_PI/180)/60)*5);
*lat+=(toupper(gs[5])-'A')*(((M_PI/180)/60)*2.5);
/* Calculate the center of the grid square */
*lon+=((M_PI/180)/60)*2.5;
*lat+=((M_PI/180)/60)*1.25;
}
}
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