NAME

       geod_init - initialize an ellipsoid
       geod_lineinit - initialize a geodesic line
       geod_position - a position on a geodesic line
       geod_direct - the direct geodesic problem
       geod_inverse - the inverse geodesic problem
       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/1.44/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\n",
                      &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/1.44/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

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

HOME PAGE

       https://github.com/OSGeo/proj.4/wiki

                                              2014/12/17 Rel. 4.9.0                                  GEODESIC(3)