Man Linux: Main Page and Category List


       geod - direct geodesic computations
       invgeod - inverse geodesic computations


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


       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 following runline control parameters can appear in any order:

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

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

       -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 coordinates and "%.3f" for

              N is the number of significant fractional digits to  employ  for
              seconds  output  (when  the  option  is  not  specified,  -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 run-line arguments 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 run 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 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 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 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=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


       The  following  script determines the geodesic azimuths and distance in
       U.S. stature miles from Boston, MA, to Portland, OR:
             geod +ellps=clrk66 <<EOF -I +units=us-mi
             42d15’N 71d07’W 45d31’N 123d41’W
       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 <<EOF +units=us-mi
             42d15’N 71d07’W -66d31’50.141" 2587.504
       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.


       Thomas,  P.D.,  1970,  Spheroidal  Geodesics, Reference Systems & Local
       Geometry: U.S. Naval Oceanographic  Office, S-138.


                              2000/03/21 Rel. 4.4                      GEOD(1)