GEOD(1)                 General Commands Manual                GEOD(1)



NAME
       geod - direct geodesic computations
       invgeod - inverse geodesic computations

SYNOPSIS
       geod +ellps=<ellipse> [ -afFIlptwW [ args ] ] [ +args ] file[s]
       invgeod  +ellps=<ellipse>  [  -afFIlptwW  [  args ] ] [ +args ]
       file[s]

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  lati‐
       tude,  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.

       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 out‐
              put.

       -ta    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.

       -[f|F] format
              Format is a printf format string to control  the  output
              form of the geographic coordinate values (f) or distance
              value (F).  The default mode is DMS for geographic coor‐
              dinates and "%.3f" for distance.

       -[w|W]n
              N  is  the  number  of  significant fractional digits to
              employ for seconds output (when the option is not speci‐
              fied,  -w3  is assumed).  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 +args command-line options  are  associated  with  geodetic
       parameters  for  specifying  the  ellipsoidal or sphere to use.
       See proj documentation for full list of  these  parameters  and
       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.

       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 speci‐
       fied, the input is assumed to be from stdin.

       For direct determinations input data must be in latitude,  lon‐
       gitude, 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 DMS format and input distance data
       must be in units consistent with the ellipsoid  major  axis  or
       sphere  radius units.  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 man‐
       ner 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=lon
       parameters   and   either   a  terminus  point  +lat_2=lat  and
       +lon_2=lon 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.

EXAMPLE
       The  following script determines the geodesic azimuths and dis‐
       tance in U.S. statute miles from Boston, MA, to Portland, OR:
             geod +ellps=clrk66 <<EOF -I +units=us-mi
             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 Port‐
       land,  the back azimuth from Portland to Boston followed by the
       distance.

       An example of forward geodesic use is to use the  Boston  loca‐
       tion and determine Portland's location by azimuth and distance:
             geod +ellps=clrk66 <<EOF +units=us-mi
             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.

SEE ALSO
       geodesic(3)

       GeographicLib, http://geographiclib.sf.net

       The GeodSolve utility in GeographicLib.  With  the  -E  option,
       this  solves  the  geodesic problems in terms of elliptic inte‐
       grals; 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

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

HOME PAGE
       http://proj.osgeo.org



                         2013/07/11 Rel. 4.9.0                 GEOD(1)