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_inverseline - initialize a geodesic line
       geod_setdistance  geod_gensetdistance   -   set   distance   to
       reference 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_testedge - 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++
       library, 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
       geodesic 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,  longitudes,  and  azimuths) in degrees, unlike the
       rest  of  the  proj   library,   which   uses   radians.    The
       documentation  for  this  library is included in geodesic.h.  A
       formatted  version  of  the  documentation  is   available   at
       http://geographiclib.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
       forward 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
       accurate 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/OSGeo/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)