diff options
| -rw-r--r-- | README.md | 34 | ||||
| -rw-r--r-- | gridcal.c | 14 |
2 files changed, 44 insertions, 4 deletions
@@ -1,9 +1,41 @@ gridcal -- compute the great-circle distance between two grid locators ====================================================================== -`gridcal` computed the short-path great-circle distance between two grid +`gridcal` computes the short-path great-circle distance between two grid locators. The Grid Locator System divides Earth into a series of rectangles identified by a combination of letters and numbers, so that the approximate position of a point can be expressed with a short identifier like IO91vl. +Usage: gridcal <loc1> [<loc2> [<pwr>]] + +If `gridcal` is given only one locator, it prints on output the latitude +and longitude of the centre of the corresponding grid square: + + gridcal IO91vl + IO91vl 51.4792 -0.208333 0.898481 -0.0036361 + +With two locators as input, `gridcal` prints on output the two locators +and their great-circle distance, both in km and miles: + + gridcal IO91vl JN65od + IO91vl JN65od 1213.71 754.164 + +If `gridcal` is given as third numerical argument, that number is +considered a "power" value in Watts, and `gridcal` will print on output +a longer line containing the two locators, the distance in km and miles, +the power value, and the corresponding km/W and miles/W: + + gridcal IO91vl JN65od 1.2 + IO91vl JN65od 1213.71 754.164 1.2 1011.42 628.47 + +The latter can be useful to check if a QSO with another ham radio +station qualifies for one of the thousand miles per Watt awards. + + +Dependencies +============ + +`gridcal` is written in ANSI C has no dependencies. + + @@ -15,8 +15,16 @@ #include <ctype.h> #define MIN(a,b) ((a)>(b)?(b):(a)) +#define R 6371 -double 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; @@ -26,7 +34,7 @@ typedef struct { void usage(char *argv0){ - printf("Usage: %s <grid1> <grid2> [<pwr>]", argv0); + printf("Usage: %s <loc1> [<loc2> [<pwr>]]", argv0); exit(1); } @@ -117,7 +125,7 @@ int main(int argc, char *argv[]){ loc1[n1] = '\0'; check_input(loc1); grid_to_latlon(loc1, &c1); - printf("%s %g %g\n", loc1, c1.lat, c1.lon); + printf("%s %g %g %g %g\n", loc1, c1.lat*180/M_PI, c1.lon*180/M_PI, c1.lat, c1.lon); exit(0); } |