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 ] ] [
11 +args ] file[s]
12 invgeod +ellps=<ellipse> [ -afFIlptwW [ args ] ]
13 [ +args ] file[s]
14
16 Geod (direct) and invgeod (inverse) perform geo‐
17 desic (Great Circle) computations for determin‐
18 ing latitude, longitude and back azimuth of a
19 terminus point given a initial point latitude,
20 longitude, azimuth and distance (direct) or the
21 forward and back azimuths and distance between
22 an initial and terminus point latitudes and lon‐
23 gitudes (inverse).
24 The following runline control parameters can
26 appear in any order:
27 -I Specifies that the inverse geodesic com‐
29 putation is to be performed. May be used
30 with execution of goed as an alternative
31 to invgeod execution.
32 -a Latitude and longitudes of the initial
34 and terminal points, forward and back
35 azimuths and distance are output.
36 -ta A specifies a character employed as the
38 first character to denote a control line
39 to be passed through without processing.
40 -le Gives a listing of all the ellipsoids
42 that may be selected with the +ellps=
43 option.
44 -lu Gives a listing of all the units that may
46 be selected with the +units= option.
47 -[f|F] format
49 Format is a printf format string to con‐
50 trol the output form of the geographic
51 coordinate values (f) or distance value
52 (F). The default mode is DMS for geo‐
53 graphic coordinates and "%.3f" for dis‐
54 tance.
55 -[w|W]n
57 N is the number of significant fractional
58 digits to employ for seconds output (when
59 the option is not specified, -w3 is
60 assumed). When -W is employed the fields
61 will be constant width with leading
62 zeroes.
63 -p This option causes the azimuthal values
65 to be output as unsigned DMS numbers
66 between 0 and 360 degrees. Also note -f.
67 The +args run-line arguments are associated with
69 geodetic parameters for specifying the ellip‐
70 soidal or sphere to use. See proj documentation
71 for full list of these parameters and controls.
72 The options are processed in left to right order
73 from the run line. Reentry of an option is
74 ignored with the first occurrence assumed to be
75 the desired value.
76 One or more files (processed in left to right
78 order) specify the source of data to be trans‐
79 formed. A - will specify the location of pro‐
80 cessing standard input. If no files are speci‐
81 fied, the input is assumed to be from stdin.
82 For direct determinations input data must be in
84 latitude, longitude, azimuth and distance order
85 and output will be latitude, longitude and back
86 azimuth of the terminus point. Latitude, longi‐
87 tude of the initial and terminus point are input
88 for the inverse mode and respective forward and
89 back azimuth from the initial and terminus
90 points are output along with the distance
91 between the points.
92 Input geographic coordinates (latitude and lon‐
94 gitude) and azimuthal data must be in DMS format
95 and input distance data must be in units consis‐
96 tent with the ellipsoid major axis or sphere
97 radius units. Output geographic coordinates
98 will be in DMS (if the -f switch is not
99 employed) to 0.001" with trailing, zero-valued
100 minute-second fields deleted. Output distance
101 data will be in the same units as the ellipsoid
102 or sphere radius.
103 The Earth's ellipsoidal figure may be selected
105 in the same manner as program proj by using
106 +ellps=, +a=, +es=, etc.
107 Geod may also be used to determine intermediate
109 points along either a geodesic line between two
110 points or along an arc of specified distance
111 from a geographic point. In both cases an ini‐
112 tial point must be specified with +lat_1=lat and
113 +lon_1=lon parameters and either a terminus
114 point +lat_2=lat and +lon_2=lon or a distance
115 and azimuth from the initial point with +S=dis‐
116 tance and +A=azimuth must be specified.
117 If points along a geodesic are to be determined
119 then either +n_S=integer specifying the number
120 of intermediate points and/or +del_S=distance
121 specifying the incremental distance between
122 points must be specified.
123 To determine points along an arc equidistant
125 from the initial point both +del_A=angle and
126 +n_A=integer must be specified which determine
127 the respective angular increments and number of
128 points to be determined.
129
131 The following script determines the geodesic
132 azimuths and distance in U.S. stature miles from
133 Boston, MA, to Portland, OR:
134 geod +ellps=clrk66 <<EOF -I +units=us-mi
135 42d15'N 71d07'W 45d31'N 123d41'W
136 EOF
137 which gives the results:
138 -66d31'50.141" 75d39'13.083" 2587.504
139 where the first two values are the azimuth from
140 Boston to Portland, the back azimuth from Port‐
141 land to Boston followed by the distance.
142 An example of forward geodesic use is to use the
144 Boston location and determine Portland's loca‐
145 tion by azimuth and distance:
146 geod +ellps=clrk66 <<EOF +units=us-mi
147 42d15'N 71d07'W -66d31'50.141" 2587.504
148 EOF
149 which gives:
150 45d31'0.003"N 123d40'59.985"W
151 75d39'13.094"
152 Note: lack of precision in the distance value
153 compromises the precision of the Portland loca‐
154 tion.
155
157 Thomas, P.D., 1970, Spheroidal Geodesics, Refer‐
158 ence Systems & Local Geometry: U.S. Naval
159 Oceanographic Office, S-138.
160
162 http://www.remotesensing.org/proj
163 2000/03/21 Rel. 4.4 GEOD(1)