/usr/bin/MagneticField

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SYNOPSIS
       MagneticField [ -n name ] [ -d dir ] [ -N Nmax ] [ -M Mmax ] [ -t time
       | -c time lat h ] [ -r ] [ -w ] [ -T tguard ] [ -H hguard ] [ -p prec ]
       [ -v ] [ --comment-delimiter commentdelim ] [ --version | -h | --help ]
       [ --input-file infile | --input-string instring ] [ --line-separator
       linesep ] [ --output-file outfile ]

DESCRIPTION
       MagneticField reads in times and positions on standard input and prints
       out the geomagnetic field on standard output and, optionally, its rate
       of change.

       The input line is of the form time lat lon h. time is a date of the
       form 2012-11-25 (yyyy-mm-dd or yyyy-mm), a fractional year such as
       2012.9, or the string "now".  lat and lon are the latitude and
       longitude expressed as decimal degrees or degrees, minutes, and
       seconds; for details on the allowed formats for latitude and longitude,
       see the "GEOGRAPHIC COORDINATES" section of GeoConvert(1).  h is the
       height above the ellipsoid in meters; this is optional and defaults to
       zero.  Alternatively, time can be given on the command line as the
       argument to the -t option, in which case it should not be included on
       the input lines.  Finally, the magnetic field can be computed at
       various points on a circle of latitude (constant time, lat, and h) via
       the -c option; in this case only the longitude should be given on the
       input lines.

       The output consists of the following 7 items:

         the declination (the direction of the horizontal component of
           the magnetic field measured clockwise from north) in degrees,
         the inclination (the direction of the magnetic field measured
           down from the horizontal) in degrees,
         the horizontal field in nanotesla (nT),
         the north component of the field in nT,
         the east component of the field in nT,
         the vertical component of the field in nT (down is positive),
         the total field in nT.

       If the -r option is given, a second line is printed giving the rates of
       change of these quantities in degrees/yr and nT/yr.

       The WGS84 ellipsoid is used, a = 6378137 m, f = 1/298.257223563.

OPTIONS
       -n name
           use magnetic field model name instead of the default "wmm2025".
           See "MODELS".

       -d dir
           read magnetic models from dir instead of the default.  See
           "MODELS".

       -N Nmax
           limit the degree of the model to Nmax.

       -M Mmax
           limit the order of the model to Mmax.

       -t time
           evaluate the field at time instead of reading the time from the
           input lines.

       -c time lat h
           evaluate the field on a circle of latitude given by time, lat, h
           instead of reading these quantities from the input lines.  In this
           case, MagneticField can calculate the field considerably more
           quickly.

       -r  toggle whether to report the rates of change of the field.

       -w  toggle the longitude first flag (it starts off); if the flag is on,
           then on input and output, longitude precedes latitude (except that,
           on input, this can be overridden by a hemisphere designator, N, S,
           E, W).

       -T tguard
           signal an error if time lies tguard years (default 50 yr) beyond
           the range for the model.

       -H hguard
           signal an error if h lies hguard meters (default 500000 m) beyond
           the range for the model.

       -p prec
           set the output precision to prec (default 1).  Fields are printed
           with precision with prec decimal places; angles use prec + 1
           places.

       -v  print information about the magnetic model on standard error before
           processing the input.

       --comment-delimiter commentdelim
           set the comment delimiter to commentdelim (e.g., "#" or "//").  If
           set, the input lines will be scanned for this delimiter and, if
           found, the delimiter and the rest of the line will be removed prior
           to processing and subsequently appended to the output line
           (separated by a space).

       --version
           print version and exit.

       -h  print usage, the default magnetic path and name, and exit.

       --help
           print full documentation and exit.

       --input-file infile
           read input from the file infile instead of from standard input; a
           file name of "-" stands for standard input.

       --input-string instring
           read input from the string instring instead of from standard input.
           All occurrences of the line separator character (default is a
           semicolon) in instring are converted to newlines before the reading
           begins.

       --line-separator linesep
           set the line separator character to linesep.  By default this is a
           semicolon.

       --output-file outfile
           write output to the file outfile instead of to standard output; a
           file name of "-" stands for standard output.

MODELS
       MagneticField computes the geomagnetic field using one of the following
       models

           wmm2010, the World Magnetic Model 2010, which approximates the
             main magnetic field for the period 2010-2015.  See
             https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
           wmm2015v2, the World Magnetic Model 2015, which approximates the
             main magnetic field for the period 2015-2020.  See
             https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
           wmm2015, a deprecated version of wmm2015v2
           wmm2020, the World Magnetic Model 2020, which approximates the
             main magnetic field for the period 2020-2025.  See
             https://ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
           wmm2025, the World Magnetic Model 2025, which approximates the
             main magnetic field for the period 2025-2030.  See
             https://www.ncei.noaa.gov/products/world-magnetic-model
           wmmhr2025, the World Magnetic Model High Resolution 2025, a high
             resolution version of wmm2025.  See
             https://www.ncei.noaa.gov/products/world-magnetic-model-high-resolution
           igrf11, the International Geomagnetic Reference Field (11th
             generation), which approximates the main magnetic field for
             the period 1900-2015.  See
             https://ngdc.noaa.gov/IAGA/vmod/igrf.html
           igrf12, the International Geomagnetic Reference Field (12th
             generation), which approximates the main magnetic field for
             the period 1900-2020.  See
             https://ngdc.noaa.gov/IAGA/vmod/igrf.html
           igrf13, the International Geomagnetic Reference Field (13th
             generation), which approximates the main magnetic field for
             the period 1900-2025.  See
             https://ngdc.noaa.gov/IAGA/vmod/igrf.html
           igrf14, the International Geomagnetic Reference Field (14th
             generation), which approximates the main magnetic field for
             the period 1900-2030.  See
             https://www.ncei.noaa.gov/products/international-geomagnetic-reference-field
           emm2010, the Enhanced Magnetic Model 2010, which approximates
             the main and crustal magnetic fields for the period 2010-2015.
             See https://ngdc.noaa.gov/geomag/EMM/index.html
           emm2015, the Enhanced Magnetic Model 2015, which approximates
             the main and crustal magnetic fields for the period 2000-2020.
             See https://ngdc.noaa.gov/geomag/EMM/index.html
           emm2017, the Enhanced Magnetic Model 2017, which approximates
             the main and crustal magnetic fields for the period 2000-2022.
             See https://ngdc.noaa.gov/geomag/EMM/index.html

       These models approximate the magnetic field due to the earth's core and
       (in the case of emm20xx) its crust.  They neglect magnetic fields due
       to the ionosphere, the magnetosphere, nearby magnetized materials,
       electrical machinery, etc.

       By default, the "wmm2025" magnetic model is used.  This may changed by
       setting the environment variable "GEOGRAPHICLIB_MAGNETIC_NAME" or with
       the -n option.

       The magnetic models will be loaded from a directory specified at
       compile time.  This may changed by setting the environment variables
       "GEOGRAPHICLIB_MAGNETIC_PATH" or "GEOGRAPHICLIB_DATA", or with the -d
       option.  The -h option prints the default magnetic path and name.  Use
       the -v option to ascertain the full path name of the data file.

       Instructions for downloading and installing magnetic models are
       available at
       <https://geographiclib.sourceforge.io/C++/doc/magnetic.html#magneticinst>.

ENVIRONMENT
       GEOGRAPHICLIB_MAGNETIC_NAME
           Override the compile-time default magnetic name of "wmm2025".  The
           -h option reports the value of GEOGRAPHICLIB_MAGNETIC_NAME, if
           defined, otherwise it reports the compile-time value.  If the -n
           name option is used, then name takes precedence.

       GEOGRAPHICLIB_MAGNETIC_PATH
           Override the compile-time default magnetic path.  This is typically
           "/usr/local/share/GeographicLib/magnetic" on Unix-like systems and
           "C:/ProgramData/GeographicLib/magnetic" on Windows systems.  The -h
           option reports the value of GEOGRAPHICLIB_MAGNETIC_PATH, if
           defined, otherwise it reports the compile-time value.  If the -d
           dir option is used, then dir takes precedence.

       GEOGRAPHICLIB_DATA
           Another way of overriding the compile-time default magnetic path.
           If it is set (and if GEOGRAPHICLIB_MAGNETIC_PATH is not set), then
           $GEOGRAPHICLIB_DATA/magnetic is used.

ERRORS
       An illegal line of input will print an error message to standard output
       beginning with "ERROR:" and causes MagneticField to return an exit code
       of 1.  However, an error does not cause MagneticField to terminate;
       following lines will be converted.  If time or h are outside the
       recommended ranges for the model (but inside the ranges increase by
       tguard and hguard), a warning is printed on standard error and the
       field (which may be inaccurate) is returned in the normal way.

EXAMPLES
       The magnetic field from WMM2025 in Timbuktu on 2025-01-01

           echo 2025-01-01 16:46:33N 3:00:34W 300 | MagneticField -r
           => -1.04 12.00 34015.6 34010.0 -618.0 7232.0 34775.9
              0.11 0.01 4.2 5.4 63.7 5.4 5.3

       The first two numbers returned are the declination and inclination of
       the field.  The second line gives the annual change.

SEE ALSO
       GeoConvert(1), geographiclib-get-magnetic(8).

AUTHOR
       MagneticField was written by Charles Karney.

HISTORY