NAME

       geod_init - initialize an ellipsoid
       geod_direct geod_gendirect - the direct geodesic problem
       geod_inverse geod_geninverse - the inverse geodesic problem
       geod_lineinit  geod_directline geod_gendirectline geod_inverse‐
       line - initialize a geodesic line
       geod_setdistance geod_gensetdistance - set distance  to  refer‐
       ence point
       geod_position geod_genposition - a position on a geodesic line
       geod_polygon_init - initialize a polygon
       geod_addpoint geod_addedge - add to a polygon
       geod_polygon_compute  geod_polygon_testpoint geod_polygon_test‐
       edge - compute properties of polygon
       geod_polygon_clear - clear polygon
       geod_polygonarea - the area of a polygon

SYNOPSIS

       #include <geodesic.h>
       and link against the proj library.

DESCRIPTION

       This library is a port of the geodesic routines in the C++  li‐
       brary,  GeographicLib,  to C.  It solves the direct and inverse
       geodesic problems on an ellipsoid of revolution.  In  addition,
       the reduced length of a geodesic and the area between a geodes‐
       ic  and  the equator can be computed.  The results are accurate
       to round off for |f| < 1/50, where f is the  flattening.   Note
       that  the  geodesic  routines measure angles (latitudes, longi‐
       tudes, and azimuths) in degrees, unlike the rest  of  the  proj
       library,  which  uses  radians.  The documentation for this li‐
       brary is included in geodesic.h.  A formatted  version  of  the
       documentation     is     available     at     http://geographi‐
       clib.sf.net/1.46/C

EXAMPLE

       The following program reads in lines with the  coordinates  for
       two  points  in  decimal  degrees  (lat1, lon1, lat2, lon2) and
       prints out azi1, azi2, s12 for the geodesic line  between  each
       pair  of points on the WGS84 ellipsoid.  (N.B. azi2 is the for‐
       ward azimuth at point 2.)

       #include <stdio.h>
       #include <geodesic.h>

       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("%.8f %.8f %.3f\n", azi1, azi2, s12);
         }
         return 0;
       }

LIBRARY

       libproj.a - library of projections and support procedures

SEE ALSO

       Full online documentation for geodesic(3),
       http://geographiclib.sf.net/1.46/C

       geod(1)

       GeographicLib, http://geographiclib.sf.net

       The GeodesicExact class in GeographicLib  solves  the  geodesic
       problems  in terms of elliptic integrals; the results are accu‐
       rate for arbitrary f.

       C. F. F. Karney, Algorithms for Geodesics,
       J. Geodesy 87, 43-55 (2013);
       DOI: http://dx.doi.org/10.1007/s00190-012-0578-z
       http://geographiclib.sf.net/geod-addenda.html

       A geodesic bibliography,
       http://geographiclib.sf.net/geodesic-papers/biblio.html

       The Wikipedia page, Geodesics on an ellipsoid,
       https://en.wikipedia.org/wiki/Geodesics_on_an_ellipsoid

BUGS

       A list  of  known  bugs  can  found  at  https://github.com/OS‐
       Geo/proj.4/issues where new bug reports can be submitted too.

HOME PAGE

       http://proj4.org/

                                              2016/02/16 Rel. 4.9.3                                  GEODESIC(3)