Provided by: geographiclib-tools_1.50.1-1build1_amd64 bug

NAME

       MagneticField -- compute the earth's magnetic field

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 2012-07-03, a
       fractional year such as 2012.5, 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 "wmm2020".  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
           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
           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 "wmm2020" 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/html/magnetic.html#magneticinst>.

ENVIRONMENT

       GEOGRAPHICLIB_MAGNETIC_NAME
           Override the compile-time default magnetic name of "wmm2020".  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 WMM2020 in Timbuktu on 2020-01-01

           echo 2020-01-01 16:46:33N 3:00:34W 300 | MagneticField -r
           => -1.60 12.00 33973.5 33960.3 -948.1 7223.0 34732.8
              0.13 -0.02 21.8 23.9 77.9 -8.4 19.5

       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

       MagneticField was added to GeographicLib, <https://geographiclib.sourceforge.io>, in
       version 1.15.