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 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	documenta-
       tion  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  pro-
       cessing 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 ellip-
       soid 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  dis-
       tance  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  speci-
       fied.

       If  points  along  a geodesic are to be determined then either +n_S=integer specifying the number of intermediate points and/or +del_S=dis-
       tance 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)