1GEOD(1) General Commands Manual GEOD(1)
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6 geod - direct geodesic computations
7 invgeod - inverse geodesic computations
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10 geod +ellps=<ellipse> [ -afFIlptwW [ args ] ] [ +args ] file[s]
11 invgeod +ellps=<ellipse> [ -afFIlptwW [ args ] ] [ +args ]
12 file[s]
13
15 geod (direct) and invgeod (inverse) perform geodesic ("Great
16 Circle") computations for determining latitude, longitude and
17 back azimuth of a terminus point given a initial point lati‐
18 tude, longitude, azimuth and distance (direct) or the forward
19 and back azimuths and distance between an initial and terminus
20 point latitudes and longitudes (inverse). The results are
21 accurate to round off for |f| < 1/50, where f is flattening.
22 invgeod may not be available on all platforms; in this case
23 call geod with the -I option.
24 The following command-line options can appear in any order:
26 -I Specifies that the inverse geodesic computation is to be
28 performed. May be used with execution of geod as an
29 alternative to invgeod execution.
30 -a Latitude and longitudes of the initial and terminal
32 points, forward and back azimuths and distance are out‐
33 put.
34 -ta A specifies a character employed as the first character
36 to denote a control line to be passed through without
37 processing.
38 -le Gives a listing of all the ellipsoids that may be
40 selected with the +ellps= option.
41 -lu Gives a listing of all the units that may be selected
43 with the +units= option.
44 -[f|F] format
46 Format is a printf format string to control the output
47 form of the geographic coordinate values (f) or distance
48 value (F). The default mode is DMS for geographic coor‐
49 dinates and "%.3f" for distance.
50 -[w|W]n
52 N is the number of significant fractional digits to
53 employ for seconds output (when the option is not speci‐
54 fied, -w3 is assumed). When -W is employed the fields
55 will be constant width with leading zeroes.
56 -p This option causes the azimuthal values to be output as
58 unsigned DMS numbers between 0 and 360 degrees. Also
59 note -f.
60 The +args command-line options are associated with geodetic
62 parameters for specifying the ellipsoidal or sphere to use.
63 See proj documentation for full list of these parameters and
64 controls. The options are processed in left to right order
65 from the command line. Reentry of an option is ignored with
66 the first occurrence assumed to be the desired value.
67 One or more files (processed in left to right order) specify
69 the source of data to be transformed. A - will specify the
70 location of processing standard input. If no files are speci‐
71 fied, the input is assumed to be from stdin.
72 For direct determinations input data must be in latitude, lon‐
74 gitude, azimuth and distance order and output will be latitude,
75 longitude and back azimuth of the terminus point. Latitude,
76 longitude of the initial and terminus point are input for the
77 inverse mode and respective forward and back azimuth from the
78 initial and terminus points are output along with the distance
79 between the points.
80 Input geographic coordinates (latitude and longitude) and
82 azimuthal data must be in decimal degrees or DMS format and
83 input distance data must be in units consistent with the ellip‐
84 soid major axis or sphere radius units. The latitude must lie
85 in the range [-90d,90d]. Output geographic coordinates will be
86 in DMS (if the -f switch is not employed) to 0.001" with trail‐
87 ing, zero-valued minute-second fields deleted. Output distance
88 data will be in the same units as the ellipsoid or sphere
89 radius.
90 The Earth's ellipsoidal figure may be selected in the same man‐
92 ner as program proj by using +ellps=, +a=, +es=, etc.
93 Geod may also be used to determine intermediate points along
95 either a geodesic line between two points or along an arc of
96 specified distance from a geographic point. In both cases an
97 initial point must be specified with +lat_1=lat and +lon_1=lon
98 parameters and either a terminus point +lat_2=lat and
99 +lon_2=lon or a distance and azimuth from the initial point
100 with +S=distance and +A=azimuth must be specified.
101 If points along a geodesic are to be determined then either
103 +n_S=integer specifying the number of intermediate points
104 and/or +del_S=distance specifying the incremental distance
105 between points must be specified.
106 To determine points along an arc equidistant from the initial
108 point both +del_A=angle and +n_A=integer must be specified
109 which determine the respective angular increments and number of
110 points to be determined.
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113 The following script determines the geodesic azimuths and dis‐
114 tance in U.S. statute miles from Boston, MA, to Portland, OR:
115 geod +ellps=clrk66 <<EOF -I +units=us-mi
116 42d15'N 71d07'W 45d31'N 123d41'W
117 EOF
118 which gives the results:
119 -66d31'50.141" 75d39'13.083" 2587.504
120 where the first two values are the azimuth from Boston to Port‐
121 land, the back azimuth from Portland to Boston followed by the
122 distance.
123 An example of forward geodesic use is to use the Boston loca‐
125 tion and determine Portland's location by azimuth and distance:
126 geod +ellps=clrk66 <<EOF +units=us-mi
127 42d15'N 71d07'W -66d31'50.141" 2587.504
128 EOF
129 which gives:
130 45d31'0.003"N 123d40'59.985"W 75d39'13.094"
131 Note: lack of precision in the distance value compromises the
132 precision of the Portland location.
133
135 geodesic(3)
136 GeographicLib, http://geographiclib.sf.net
138 The GeodSolve utility in GeographicLib. With the -E option,
140 this solves the geodesic problems in terms of elliptic inte‐
141 grals; the results are accurate for arbitrary f.
142 C. F. F. Karney, Algorithms for Geodesics,
144 J. Geodesy 87, 43-55 (2013);
145 DOI: http://dx.doi.org/10.1007/s00190-012-0578-z
146 http://geographiclib.sf.net/geod-addenda.html
147 The online geodesic bibliography,
149 http://geographiclib.sf.net/geodesic-papers/biblio.html
150
152 A list of known bugs can found at
153 https://github.com/OSGeo/proj.4/issues where new bug reports
154 can be submitted too.
155
157 http://proj4.org/
158 2016/02/16 Rel. 4.9.3 GEOD(1)