GEOD(1) PROJ GEOD(1)
NAME
geod - Geodesic computations
SYNOPSIS
geod +ellps=<ellipse> [-afFIlptwW [args]] [+opt[=arg] ...] file ...
invgeod +ellps=<ellipse> [-afFIlptwW [args]] [+opt[=arg] ...] file
...
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
results are accurate to round off for |f| < 1/50, where f is flatten-
ing.
invgeod may not be available on all platforms; in this case use geod -I
instead.
The following command-line options can appear in any order:
-I Specifies that the inverse geodesic computation is to be per-
formed. May be used with execution of geod as an alternative to
invgeod execution.
-a Latitude and longitudes of the initial and terminal points, for-
ward and back azimuths and distance are output.
-t<a> Where 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. (Default units are meters.)
-f <format>
Where format is a printf format string to control the output
form of the geographic coordinate values. The default mode is
DMS.
-F <format>
Where format is a printf format string to control the output
form of the distance value. The default mode is "%.3f".
-w<n> Where n is the number of significant fractional digits to employ
for seconds output (when the option is not specified, -w3 is as-
sumed).
-W<n> Where n is the number of significant fractional digits to employ
for seconds output. When -W is employed the fields will be con-
stant 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 +opt command-line options are associated with geodetic parameters
for specifying the ellipsoidal or sphere to use. 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 de-
sired value.
See the PROJ documentation for a full list of these parameters and con-
trols.
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 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 decimal degrees or DMS format and input distance data
must be in units consistent with the ellipsoid major axis or sphere ra-
dius units. The latitude must lie in the range [-90d,90d]. Output geo-
graphic coordinates will be in DMS (if the -f switch is not employed)
to 0.001" with trailing, zero-valued minute-second fields deleted. Out-
put 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 speci-
fied 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 ini-
tial point with +S=distance and +A=azimuth must be specified.
If points along a geodesic are to be determined then either +n_S=inte-
ger 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 deter-
mined.
EXAMPLES
The following script determines the geodesic azimuths and distance in
U.S. statute miles from Boston, MA, to Portland, 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 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 +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.
FURTHER READING
1. GeographicLib.
2. C. F. F. Karney, Algorithms for Geodesics, J. Geodesy 87(1), 43–55
(2013); addenda.
3. A geodesic bibliography.
SEE ALSO
proj(1), cs2cs(1), cct(1), gie(1), projinfo(1), projsync(1)
BUGS
A list of known bugs can be found at
https://github.com/OSGeo/PROJ/issues where new bug reports can be sub-
mitted to.
HOME PAGE
https://proj.org/
AUTHOR
Charles Karney
COPYRIGHT
1983-2022
9.1.1 Dec 1st, 2022 GEOD(1)
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