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NAME

       geod - Geodesic computations

SYNOPSIS

          geod +ellps=<ellipse> [-afFIlptwW [args]] [+opt[=arg] ...] file ...

          invgeod +ellps=<ellipse> [-afFIlptwW [args]] [+opt[=arg] ...] file ...

DESCRIPTION

       geod  (direct)  and  invgeod  (inverse)  perform  geodesic (Great Circle) computations for
       determining latitude, longitude and back azimuth of a terminus point given a initial point
       latitude,  longitude,  azimuth  and distance (direct) or the forward and back azimuths and
       distance between an initial and terminus point latitudes and  longitudes  (inverse).   The
       results are accurate to round off for |f| < 1/50, where f is flattening.

       invgeod may not be available on all platforms; in this case use geod -I instead.

       The following command-line options can appear in any order:

       -I     Specifies  that  the  inverse  geodesic computation is to be performed. May be used
              with execution of geod as an alternative to invgeod execution.

       -a     Latitude and longitudes of the  initial  and  terminal  points,  forward  and  back
              azimuths and distance are output.

       -t<a>  Where  a  specifies a character employed as the first character to denote a control
              line to be passed through without processing.

       -le    Gives a listing of all the ellipsoids that may be selected with the +ellps= option.

       -lu    Gives a listing of all the units that may be  selected  with  the  +units=  option.
              (Default units are meters.)

       -f <format>
              Where format is a printf format string to control the output form of the geographic
              coordinate values. The default mode is DMS.

       -F <format>
              Where format is a printf format string to control the output form of  the  distance
              value. The default mode is "%.3f".

       -w<n>  Where n is the number of significant fractional digits to employ for seconds output
              (when the option is not specified, -w3 is assumed).

       -W<n>  Where n is the number of  significant  fractional  digits  to  employ  for  seconds
              output. When -W is employed the fields will be constant width with leading zeroes.

       -p     This  option  causes  the  azimuthal  values  to  be output as unsigned DMS numbers
              between 0 and 360 degrees. Also note -f.

       The +opt command-line options are associated with geodetic parameters for  specifying  the
       ellipsoidal  or sphere to use.  controls. The options are processed in left to right order
       from the command line. Reentry of an option is ignored with the first  occurrence  assumed
       to be the desired value.

       See the PROJ documentation for a full list of these parameters and controls.

       One  or  more  files  (processed  in left to right order) specify the source of data to be
       transformed. A - will specify the location of processing standard input. If no  files  are
       specified, the input is assumed to be from stdin.

       For  direct determinations input data must be in latitude, longitude, azimuth and distance
       order and output will be latitude, longitude and  back  azimuth  of  the  terminus  point.
       Latitude,  longitude  of the initial and terminus point are input for the inverse mode and
       respective forward and back azimuth from the initial and terminus points are output  along
       with the distance between the points.

       Input  geographic  coordinates  (latitude  and  longitude)  and  azimuthal data must be in
       decimal degrees or DMS format and input distance data must be in units consistent with the
       ellipsoid  major  axis  or  sphere  radius  units.  The  latitude  must  lie  in the range
       [-90d,90d]. Output geographic coordinates will  be  in  DMS  (if  the  -f  switch  is  not
       employed)  to  0.001"  with  trailing,  zero-valued  minute-second  fields deleted. Output
       distance data will be in the same units as the ellipsoid or sphere radius.

       The Earth's ellipsoidal figure may be selected in the same manner as program proj by using
       +ellps=, +a=, +es=, etc.

       geod  may  also  be  used  to  determine  intermediate points along either a geodesic line
       between two points or along an arc of specified distance from a geographic point. In  both
       cases  an  initial  point must be specified with +lat_1=lat and +lon_1=long parameters and
       either a terminus point +lat_2=lat and +lon_2=long or a  distance  and  azimuth  from  the
       initial point with +S=distance and +A=azimuth must be specified.

       If  points  along  a geodesic are to be determined then either +n_S=integer specifying the
       number of intermediate points and/or +del_S=distance specifying the  incremental  distance
       between points must be specified.

       To  determine points along an arc equidistant from the initial point both +del_A=angle and
       +n_A=integer must be specified which  determine  the  respective  angular  increments  and
       number of points to be determined.

EXAMPLES

       The  following script determines the geodesic azimuths and distance in U.S.  statute miles
       from Boston, MA, to Portland, OR:

          geod +ellps=clrk66 -I +units=us-mi <<EOF
          42d15'N 71d07'W 45d31'N 123d41'W
          EOF

       which gives the results:

          -66d31'50.141" 75d39'13.083" 2587.504

       where the first two values are the azimuth from Boston to Portland, the back azimuth  from
       Portland to Boston followed by the distance.

       An  example of forward geodesic use is to use the Boston location and determine Portland's
       location by azimuth and distance:

          geod +ellps=clrk66 +units=us-mi <<EOF
          42d15'N 71d07'W -66d31'50.141" 2587.504
          EOF

       which gives:

          45d31'0.003"N 123d40'59.985"W 75d39'13.094"

       NOTE:
          Lack of precision in the distance value  compromises  the  precision  of  the  Portland
          location.

FURTHER READING

       1. GeographicLib.

       2. C. F. F. Karney, Algorithms for Geodesics, J. Geodesy 87(1), 43–55 (2013); addenda.

       3. A geodesic bibliography.

SEE ALSO

       proj(1), cs2cs(1), cct(1), gie(1), projinfo(1), projsync(1)

BUGS

       A  list  of  known bugs can be found at https://github.com/OSGeo/PROJ/issues where new bug
       reports can be submitted to.

HOME PAGE

       https://proj.org/

AUTHOR

       Charles Karney

COPYRIGHT

       1983-2023