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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"

       i.e., the latitude and longitude of Portland, and the back azimuth from Portland to Boston.

       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

       1983-2024, PROJ contributors