1MAGNETICFIELD(1) GeographicLib Utilities MAGNETICFIELD(1)
2
6 MagneticField -- compute the earth's magnetic field
7
9 MagneticField [ -n name ] [ -d dir ] [ -N Nmax ] [ -M Mmax ] [ -t time
10 | -c time lat h ] [ -r ] [ -w ] [ -T tguard ] [ -H hguard ] [ -p prec ]
11 [ -v ] [ --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.
49
51 -n name
52 use magnetic field model name instead of the default "wmm2020".
53 See "MODELS".
54 -d dir
56 read magnetic models from dir instead of the default. See
57 "MODELS".
58 -N Nmax
60 limit the degree of the model to Nmax.
61 -M Mmax
63 limit the order of the model to Mmax.
64 -t time
66 evaluate the field at time instead of reading the time from the
67 input lines.
68 -c time lat h
70 evaluate the field on a circle of latitude given by time, lat, h
71 instead of reading these quantities from the input lines. In this
72 case, MagneticField can calculate the field considerably more
73 quickly.
74 -r toggle whether to report the rates of change of the field.
76 -w toggle the longitude first flag (it starts off); if the flag is on,
78 then on input and output, longitude precedes latitude (except that,
79 on input, this can be overridden by a hemisphere designator, N, S,
80 E, W).
81 -T tguard
83 signal an error if time lies tguard years (default 50 yr) beyond
84 the range for the model.
85 -H hguard
87 signal an error if h lies hguard meters (default 500000 m) beyond
88 the range for the model.
89 -p prec
91 set the output precision to prec (default 1). Fields are printed
92 with precision with prec decimal places; angles use prec + 1
93 places.
94 -v print information about the magnetic model on standard error before
96 processing the input.
97 --comment-delimiter commentdelim
99 set the comment delimiter to commentdelim (e.g., "#" or "//"). If
100 set, the input lines will be scanned for this delimiter and, if
101 found, the delimiter and the rest of the line will be removed prior
102 to processing and subsequently appended to the output line
103 (separated by a space).
104 --version
106 print version and exit.
107 -h print usage, the default magnetic path and name, and exit.
109 --help
111 print full documentation and exit.
112 --input-file infile
114 read input from the file infile instead of from standard input; a
115 file name of "-" stands for standard input.
116 --input-string instring
118 read input from the string instring instead of from standard input.
119 All occurrences of the line separator character (default is a
120 semicolon) in instring are converted to newlines before the reading
121 begins.
122 --line-separator linesep
124 set the line separator character to linesep. By default this is a
125 semicolon.
126 --output-file outfile
128 write output to the file outfile instead of to standard output; a
129 file name of "-" stands for standard output.
130
132 MagneticField computes the geomagnetic field using one of the following
133 models
134 wmm2010, the World Magnetic Model 2010, which approximates the
136 main magnetic field for the period 2010-2015. See
137 https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
138 wmm2015v2, the World Magnetic Model 2015, which approximates the
139 main magnetic field for the period 2015-2020. See
140 https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
141 wmm2015, a deprecated version of wmm2015v2
142 wmm2020, the World Magnetic Model 2020, which approximates the
143 main magnetic field for the period 2020-2025. See
144 https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
145 igrf11, the International Geomagnetic Reference Field (11th
146 generation), which approximates the main magnetic field for
147 the period 1900-2015. See
148 https://ngdc.noaa.gov/IAGA/vmod/igrf.html
149 igrf12, the International Geomagnetic Reference Field (12th
150 generation), which approximates the main magnetic field for
151 the period 1900-2020. See
152 https://ngdc.noaa.gov/IAGA/vmod/igrf.html
153 igrf13, the International Geomagnetic Reference Field (13th
154 generation), which approximates the main magnetic field for
155 the period 1900-2025. See
156 https://ngdc.noaa.gov/IAGA/vmod/igrf.html
157 emm2010, the Enhanced Magnetic Model 2010, which approximates
158 the main and crustal magnetic fields for the period 2010-2015.
159 See https://ngdc.noaa.gov/geomag/EMM/index.html
160 emm2015, the Enhanced Magnetic Model 2015, which approximates
161 the main and crustal magnetic fields for the period 2000-2020.
162 See https://ngdc.noaa.gov/geomag/EMM/index.html
163 emm2017, the Enhanced Magnetic Model 2017, which approximates
164 the main and crustal magnetic fields for the period 2000-2022.
165 See https://ngdc.noaa.gov/geomag/EMM/index.html
166 These models approximate the magnetic field due to the earth's core and
168 (in the case of emm20xx) its crust. They neglect magnetic fields due
169 to the ionosphere, the magnetosphere, nearby magnetized materials,
170 electrical machinery, etc.
171 By default, the "wmm2020" magnetic model is used. This may changed by
173 setting the environment variable "GEOGRAPHICLIB_MAGNETIC_NAME" or with
174 the -n option.
175 The magnetic models will be loaded from a directory specified at
177 compile time. This may changed by setting the environment variables
178 "GEOGRAPHICLIB_MAGNETIC_PATH" or "GEOGRAPHICLIB_DATA", or with the -d
179 option. The -h option prints the default magnetic path and name. Use
180 the -v option to ascertain the full path name of the data file.
181 Instructions for downloading and installing magnetic models are
183 available at
184 <https://geographiclib.sourceforge.io/html/magnetic.html#magneticinst>.
185
187 GEOGRAPHICLIB_MAGNETIC_NAME
188 Override the compile-time default magnetic name of "wmm2020". The
189 -h option reports the value of GEOGRAPHICLIB_MAGNETIC_NAME, if
190 defined, otherwise it reports the compile-time value. If the -n
191 name option is used, then name takes precedence.
192 GEOGRAPHICLIB_MAGNETIC_PATH
194 Override the compile-time default magnetic path. This is typically
195 "/usr/local/share/GeographicLib/magnetic" on Unix-like systems and
196 "C:/ProgramData/GeographicLib/magnetic" on Windows systems. The -h
197 option reports the value of GEOGRAPHICLIB_MAGNETIC_PATH, if
198 defined, otherwise it reports the compile-time value. If the -d
199 dir option is used, then dir takes precedence.
200 GEOGRAPHICLIB_DATA
202 Another way of overriding the compile-time default magnetic path.
203 If it is set (and if GEOGRAPHICLIB_MAGNETIC_PATH is not set), then
204 $GEOGRAPHICLIB_DATA/magnetic is used.
205
207 An illegal line of input will print an error message to standard output
208 beginning with "ERROR:" and causes MagneticField to return an exit code
209 of 1. However, an error does not cause MagneticField to terminate;
210 following lines will be converted. If time or h are outside the
211 recommended ranges for the model (but inside the ranges increase by
212 tguard and hguard), a warning is printed on standard error and the
213 field (which may be inaccurate) is returned in the normal way.
214
216 The magnetic field from WMM2020 in Timbuktu on 2020-01-01
217 echo 2020-01-01 16:46:33N 3:00:34W 300 | MagneticField -r
219 => -1.60 12.00 33973.5 33960.3 -948.1 7223.0 34732.8
220 0.13 -0.02 21.8 23.9 77.9 -8.4 19.5
221 The first two numbers returned are the declination and inclination of
223 the field. The second line gives the annual change.
224
226 GeoConvert(1), geographiclib-get-magnetic(8).
227
229 MagneticField was written by Charles Karney.
230
232 MagneticField was added to GeographicLib,
233 <https://geographiclib.sourceforge.io>, in version 1.15.
234GeographicLib 1.51 2020-11-22 MAGNETICFIELD(1)