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  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
              distance.

       -[w|W]n
              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
       determined.

EXAMPLE

       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
             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 <<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

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

HOME PAGE

       http://www.remotesensing.org/proj

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