-// magvar.hxx -- compute local magnetic variation given position,
-// altitude, and date
-//
-// This is an implimentation of the NIMA WMM 2000
-//
-// http://www.nima.mil/GandG/ngdc-wmm2000.html
-//
-// Copyright (C) 2000 Edward A Williams <Ed_Williams@compuserve.com>
+/**
+ * \file magvar.hxx
+ * Magnetic variation wrapper class.
+ */
+
+// Written by Curtis Olson, started July 2000.
//
-// Adapted from Excel 3.0 version 3/27/94 EAW
-// Recoded in C++ by Starry Chan
-// WMM95 added and rearranged in ANSI-C EAW 7/9/95
-// Put shell around program and made Borland & GCC compatible EAW 11/22/95
-// IGRF95 added 2/96 EAW
-// WMM2000 IGR2000 added 2/00 EAW
-// Released under GPL 3/26/00 EAW
-// Adaptions and modifications for the SimGear project 3/27/2000 CLO
+// Copyright (C) 2000 Curtis L. Olson - http://www.flightgear.org/~curt
//
-// This library is free software; you can redistribute it and/or
-// modify it under the terms of the GNU Library General Public
-// License as published by the Free Software Foundation; either
-// version 2 of the License, or (at your option) any later version.
+// This program is free software; you can redistribute it and/or
+// modify it under the terms of the GNU General Public License as
+// published by the Free Software Foundation; either version 2 of the
+// License, or (at your option) any later version.
//
-// This library is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// This program is distributed in the hope that it will be useful, but
+// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
-// Library General Public License for more details.
+// General Public License for more details.
//
-// You should have received a copy of the GNU Library General Public
-// License along with this library; if not, write to the
-// Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-// Boston, MA 02111-1307, USA.
+// You should have received a copy of the GNU General Public License
+// along with this program; if not, write to the Free Software
+// Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
//
// $Id$
-#ifndef SG_MAGVAR_HXX
-#define SG_MAGVAR_HXX
+#ifndef _MAGVAR_HXX
+#define _MAGVAR_HXX
+
+
+#ifndef __cplusplus
+# error This library requires C++
+#endif
+
+
+// forward decls
+class SGGeod;
+
+/**
+ * Magnetic variation wrapper class.
+ *
+ * The SGMagVar class calculates the magnetic variation and dip for
+ * any position, altitude, and time. It is a complete
+ * re-implimentation of the NIMA WMM 2000 (not derived from their demo
+ * code.)
+ *
+ * The SGMagVar class is really a simple wrapper around the core Ed
+ * Williams code which does all the hard work. This class allows you
+ * to crunch the math once and then do multiple polls of the
+ * data. However, if your position, altitude, or time has changed
+ * significantly, you should call the update() method to recrunch new
+ * numbers.
+ */
+class SGMagVar {
+
+private:
+
+ double magvar;
+ double magdip;
+
+public:
+
+ /**
+ * This creates an instance of the SGMagVar object.
+ * You must call the update() method before any queries will be valid.
+ */
+ SGMagVar();
+
+ /** Destructor */
+ ~SGMagVar();
+
+ /** Recalculate the magnetic offset and dip.
+ * The update() method requires you to pass in your position and
+ * the julian date. Lon and lat are specified in radians, altitude
+ * is specified in meters. Julian date can be conveniently
+ * calculated by using an instance of the SGTime class.
+ * @param lon longitude in radians
+ * @param lat latitude in radians
+ * @param alt_m altitude above sea level in meters
+ * @param jd julian date
+ */
+ void update( double lon, double lat, double alt_m, double jd );
+ /**
+ * overloaded variant taking an SGGeod to specify position
+ */
+ void update( const SGGeod& geod, double jd );
-/* Convert date to Julian day 1950-2049 */
-unsigned long int yymmdd_to_julian_days( int yy, int mm, int dd );
+ /** @return the current magnetic variation in radians. */
+ double get_magvar() const { return magvar; }
-/* Convert degrees to radians */
-double deg_to_rad( double deg );
+ /** @return the current magnetic dip in radians. */
+ double get_magdip() const { return magdip; }
+};
-/* Convert radians to degrees */
-double rad_to_deg( double rad );
-/* return variation (in degrees) given geodetic latitude (radians), longitude
-(radians) ,height (km) and (Julian) date
-N and E lat and long are positive, S and W negative
-*/
-double SGMagVar( double lat, double lon, double h, long dat, double* field );
+/**
+ * \relates SGMagVar
+ * Lookup the magvar for any arbitrary location (This function doesn't
+ * save state like the SGMagVar class. This function triggers a fair
+ * amount of CPU work, so use it cautiously.
+ * @return the magvar in radians
+ */
+double sgGetMagVar( double lon, double lat, double alt_m, double jd );
+/**
+ * overload version of the above to take a SGGeod
+ */
+double sgGetMagVar( const SGGeod& pos, double jd );
-#endif // SG_MAGVAR_HXX
+#endif // _MAGVAR_HXX
projects / simgear.git / blobdiff