3 * Magnetic variation wrapper class.
6 // Written by Curtis Olson, started July 2000.
8 // Copyright (C) 2000 Curtis L. Olson - http://www.flightgear.org/~curt
10 // This program is free software; you can redistribute it and/or
11 // modify it under the terms of the GNU General Public License as
12 // published by the Free Software Foundation; either version 2 of the
13 // License, or (at your option) any later version.
15 // This program is distributed in the hope that it will be useful, but
16 // WITHOUT ANY WARRANTY; without even the implied warranty of
17 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 // General Public License for more details.
20 // You should have received a copy of the GNU General Public License
21 // along with this program; if not, write to the Free Software
22 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
32 # error This library requires C++
40 * Magnetic variation wrapper class.
42 * The SGMagVar class calculates the magnetic variation and dip for
43 * any position, altitude, and time. It is a complete
44 * re-implimentation of the NIMA WMM 2000 (not derived from their demo
47 * The SGMagVar class is really a simple wrapper around the core Ed
48 * Williams code which does all the hard work. This class allows you
49 * to crunch the math once and then do multiple polls of the
50 * data. However, if your position, altitude, or time has changed
51 * significantly, you should call the update() method to recrunch new
64 * This creates an instance of the SGMagVar object.
65 * You must call the update() method before any queries will be valid.
72 /** Recalculate the magnetic offset and dip.
73 * The update() method requires you to pass in your position and
74 * the julian date. Lon and lat are specified in radians, altitude
75 * is specified in meters. Julian date can be conveniently
76 * calculated by using an instance of the SGTime class.
77 * @param lon longitude in radians
78 * @param lat latitude in radians
79 * @param alt_m altitude above sea level in meters
80 * @param jd julian date
82 void update( double lon, double lat, double alt_m, double jd );
85 * overloaded variant taking an SGGeod to specify position
87 void update( const SGGeod& geod, double jd );
89 /** @return the current magnetic variation in radians. */
90 double get_magvar() const { return magvar; }
92 /** @return the current magnetic dip in radians. */
93 double get_magdip() const { return magdip; }
99 * Lookup the magvar for any arbitrary location (This function doesn't
100 * save state like the SGMagVar class. This function triggers a fair
101 * amount of CPU work, so use it cautiously.
102 * @return the magvar in radians
104 double sgGetMagVar( double lon, double lat, double alt_m, double jd );
107 * overload version of the above to take a SGGeod
109 double sgGetMagVar( const SGGeod& pos, double jd );
111 #endif // _MAGVAR_HXX