Use as a standalone library

The PROJ library (especially as provided as part of a Linux distribution) may lag behind the code documented here by about a year.

Download the source code from as a tarball from

• https://sourceforge.net/projects/geographiclib/files/distrib-C

or check out the source code from

• https://github.com/geographiclib/geographiclib-c

Build the code with cmake

cmake -B BUILD -S .
cd BUILD
make
make test

possibly including some options via -D:

• CONVERT_WARNINGS_TO_ERRORS warnings are fatal (default ON)
• BUILD_DOCUMENTATION look for doxgen and build documentation (default ON)
• BUILD_SHARED_LIBS make a shared (instead of static) library (default ON)

CMake code to install the library is not provided.

The library consists of two files geodesic.c and geodesic.h.

Licensed under the MIT/X11 License; see LICENSE.txt.

Also included are 3 small test programs:

• direct.c is a simple command line utility for solving the direct geodesic problem;
• inverse.c is a simple command line utility for solving the inverse geodesic problem;
• planimeter.c is a simple command line utility for computing the area of a geodesic polygon given its vertices.

Here, for example, is inverse.c

/**
 * @file inverse.c
 * @brief A test program for geod_inverse()
 **********************************************************************/
 
#include <stdio.h>
#include "geodesic.h"
 
#if defined(_MSC_VER)
/* Squelch warnings about scanf */
#  pragma warning (disable: 4996)
#endif
 
/**
 * A simple program to solve the inverse geodesic problem.
 *
 * This program reads in lines with lat1, lon1, lat2, lon2 and prints out lines
 * with azi1, azi2, s12 (for the WGS84 ellipsoid).
 **********************************************************************/
 
int main() {
  double a = 6378137, f = 1/298.257223563; /* WGS84 */
  double lat1, lon1, azi1, lat2, lon2, azi2, s12;
  struct geod_geodesic g;
 
  geod_init(&g, a, f);
  while (scanf("%lf %lf %lf %lf", &lat1, &lon1, &lat2, &lon2) == 4) {
    geod_inverse(&g, lat1, lon1, lat2, lon2, &s12, &azi1, &azi2);
    printf("%.15f %.15f %.10f\n", azi1, azi2, s12);
  }
  return 0;
}

Use inverse, for example, with

echo -30 0 29.5 179.5 | ./tools/inverse