1MAGNETICFIELD(1) GeographicLib Utilities MAGNETICFIELD(1)
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6 MagneticField -- compute the earth's magnetic field
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9 MagneticField [ -n name ] [ -d dir ] [ -t time | -c time lat h ] [ -r ]
10 [ -w ] [ -T tguard ] [ -H hguard ] [ -p prec ] [ -v ] [
11 --comment-delimiter commentdelim ] [ --version | -h | --help ] [
12 --input-file infile | --input-string instring ] [ --line-separator
13 linesep ] [ --output-file outfile ]
14
16 MagneticField reads in times and positions on standard input and prints
17 out the geomagnetic field on standard output and, optionally, its rate
18 of change.
19 The input line is of the form time lat lon h. time is a date of the
21 form 2012-07-03, a fractional year such as 2012.5, or the string "now".
22 lat and lon are the latitude and longitude expressed as decimal degrees
23 or degrees, minutes, and seconds; for details on the allowed formats
24 for latitude and longitude, see the "GEOGRAPHIC COORDINATES" section of
25 GeoConvert(1). h is the height above the ellipsoid in meters; this is
26 optional and defaults to zero. Alternatively, time can be given on the
27 command line as the argument to the -t option, in which case it should
28 not be included on the input lines. Finally, the magnetic field can be
29 computed at various points on a circle of latitude (constant time, lat,
30 and h) via the -c option; in this case only the longitude should be
31 given on the input lines.
32 The output consists of the following 7 items:
34 the declination (the direction of the horizontal component of
36 the magnetic field measured clockwise from north) in degrees,
37 the inclination (the direction of the magnetic field measured
38 down from the horizontal) in degrees,
39 the horizontal field in nanotesla (nT),
40 the north component of the field in nT,
41 the east component of the field in nT,
42 the vertical component of the field in nT (down is positive),
43 the total field in nT.
44 If the -r option is given, a second line is printed giving the rates of
46 change of these quantities in degrees/yr and nT/yr.
47 The WGS84 ellipsoid is used, a = 6378137 m, f = 1/298.257223563.
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51 -n name
52 use magnetic field model name instead of the default "wmm2015".
53 See "MODELS".
54 -d dir
56 read magnetic models from dir instead of the default. See
57 "MODELS".
58 -t time
60 evaluate the field at time instead of reading the time from the
61 input lines.
62 -c time lat h
64 evaluate the field on a circle of latitude given by time, lat, h
65 instead of reading these quantities from the input lines. In this
66 case, MagneticField can calculate the field considerably more
67 quickly.
68 -r toggle whether to report the rates of change of the field.
70 -w toggle the longitude first flag (it starts off); if the flag is on,
72 then on input and output, longitude precedes latitude (except that,
73 on input, this can be overridden by a hemisphere designator, N, S,
74 E, W).
75 -T tguard
77 signal an error if time lies tguard years (default 50 yr) beyond
78 the range for the model.
79 -H hguard
81 signal an error if h lies hguard meters (default 500000 m) beyond
82 the range for the model.
83 -p prec
85 set the output precision to prec (default 1). Fields are printed
86 with precision with prec decimal places; angles use prec + 1
87 places.
88 -v print information about the magnetic model on standard error before
90 processing the input.
91 --comment-delimiter commentdelim
93 set the comment delimiter to commentdelim (e.g., "#" or "//"). If
94 set, the input lines will be scanned for this delimiter and, if
95 found, the delimiter and the rest of the line will be removed prior
96 to processing and subsequently appended to the output line
97 (separated by a space).
98 --version
100 print version and exit.
101 -h print usage, the default magnetic path and name, and exit.
103 --help
105 print full documentation and exit.
106 --input-file infile
108 read input from the file infile instead of from standard input; a
109 file name of "-" stands for standard input.
110 --input-string instring
112 read input from the string instring instead of from standard input.
113 All occurrences of the line separator character (default is a
114 semicolon) in instring are converted to newlines before the reading
115 begins.
116 --line-separator linesep
118 set the line separator character to linesep. By default this is a
119 semicolon.
120 --output-file outfile
122 write output to the file outfile instead of to standard output; a
123 file name of "-" stands for standard output.
124
126 MagneticField computes the geomagnetic field using one of the following
127 models
128 wmm2010, the World Magnetic Model 2010, which approximates the
130 main magnetic field for the period 2010-2015. See
131 https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
132 wmm2015, the World Magnetic Model 2015, which approximates the
133 main magnetic field for the period 2015-2020. See
134 https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
135 igrf11, the International Geomagnetic Reference Field (11th
136 generation), which approximates the main magnetic field for
137 the period 1900-2015. See
138 https://ngdc.noaa.gov/IAGA/vmod/igrf.html
139 igrf12, the International Geomagnetic Reference Field (12th
140 generation), which approximates the main magnetic field for
141 the period 1900-2020. See
142 https://ngdc.noaa.gov/IAGA/vmod/igrf.html
143 emm2010, the Enhanced Magnetic Model 2010, which approximates
144 the main and crustal magnetic fields for the period 2010-2015.
145 See https://ngdc.noaa.gov/geomag/EMM/index.html
146 emm2015, the Enhanced Magnetic Model 2015, which approximates
147 the main and crustal magnetic fields for the period 2000-2020.
148 See https://ngdc.noaa.gov/geomag/EMM/index.html
149 emm2017, the Enhanced Magnetic Model 2017, which approximates
150 the main and crustal magnetic fields for the period 2000-2022.
151 See https://ngdc.noaa.gov/geomag/EMM/index.html
152 These models approximate the magnetic field due to the earth's core and
154 (in the case of emm20xx) its crust. They neglect magnetic fields due
155 to the ionosphere, the magnetosphere, nearby magnetized materials,
156 electrical machinery, etc.
157 By default, the "wmm2015" magnetic model is used. This may changed by
159 setting the environment variable "GEOGRAPHICLIB_MAGNETIC_NAME" or with
160 the -n option.
161 The magnetic models will be loaded from a directory specified at
163 compile time. This may changed by setting the environment variables
164 "GEOGRAPHICLIB_MAGNETIC_PATH" or "GEOGRAPHICLIB_DATA", or with the -d
165 option. The -h option prints the default magnetic path and name. Use
166 the -v option to ascertain the full path name of the data file.
167 Instructions for downloading and installing magnetic models are
169 available at
170 <https://geographiclib.sourceforge.io/html/magnetic.html#magneticinst>.
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173 GEOGRAPHICLIB_MAGNETIC_NAME
174 Override the compile-time default magnetic name of "wmm2015". The
175 -h option reports the value of GEOGRAPHICLIB_MAGNETIC_NAME, if
176 defined, otherwise it reports the compile-time value. If the -n
177 name option is used, then name takes precedence.
178 GEOGRAPHICLIB_MAGNETIC_PATH
180 Override the compile-time default magnetic path. This is typically
181 "/usr/local/share/GeographicLib/magnetic" on Unix-like systems and
182 "C:/ProgramData/GeographicLib/magnetic" on Windows systems. The -h
183 option reports the value of GEOGRAPHICLIB_MAGNETIC_PATH, if
184 defined, otherwise it reports the compile-time value. If the -d
185 dir option is used, then dir takes precedence.
186 GEOGRAPHICLIB_DATA
188 Another way of overriding the compile-time default magnetic path.
189 If it is set (and if GEOGRAPHICLIB_MAGNETIC_PATH is not set), then
190 $GEOGRAPHICLIB_DATA/magnetic is used.
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193 An illegal line of input will print an error message to standard output
194 beginning with "ERROR:" and causes MagneticField to return an exit code
195 of 1. However, an error does not cause MagneticField to terminate;
196 following lines will be converted. If time or h are outside the
197 recommended ranges for the model (but inside the ranges increase by
198 tguard and hguard), a warning is printed on standard error and the
199 field (which may be inaccurate) is returned in the normal way.
200
202 The magnetic field from WMM2015 in Timbuktu on 2016-01-01
203 echo 2016-01-01 16:46:33N 3:00:34W 300 | MagneticField -r
205 => -2.12 12.15 33871.9 33848.7 -1251.4 7293.9 34648.3
206 0.09 -0.08 31.8 33.8 53.7 -41.4 22.3
207 The first two numbers returned are the declination and inclination of
209 the field. The second line gives the annual change.
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212 GeoConvert(1), geographiclib-get-magnetic(8).
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215 MagneticField was written by Charles Karney.
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218 MagneticField was added to GeographicLib,
219 <https://geographiclib.sourceforge.io>, in version 1.15.
220GeographicLib 1.49 2017-10-05 MAGNETICFIELD(1)