GEOD(1)GEOD(1)NAMEgeod - direct geodesic computations
invgeod - inverse geodesic computations
SYNOPSISgeod [ -afFIlptwW [ args ] ] [ +args ] file[s]
invgeod [ -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 longi
tudes (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 char
acter 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 out
put as unsigned numbers between 0 and 360.
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 param
eters and contrl. The options are processed in left to
right order from the run line. Reentry of an option is
ignored with the first occurance assumed to be the desired
value.
One or more files (processed in left to right order) spec
ify the source of data to be transformed. A - will spec
ify 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 for
ward 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 coordi
nates 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 ini
tial point both +del_A=angle and +n_A=integer must be
specified which determine the respective angular incre
ments 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 Port
land, 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 fol
lowed 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"
Note: lack of precision in the distance value compromises
the precision of the Portland location.
SEE ALSO
Thomas, P.D., 1970, Spheroidal Geodesics, Reference Sys_
tems & Local Geometry: U.S. Naval Oceanographic Office,
S-138.
HOME PAGE
http://www.remotesensing.org/proj
2000/03/21 Rel. 4.4 GEOD(1)
