This file contains the source for deriving geomagnetic variables from geodetic coordinates. More...

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "geoStars.h"

Include dependency graph for geoMag.c:

Macros
#define	wmmData wmmDta2010

#define	EPOCH 2010.0

#define	snorm p

#define	MAXDEG 12

Functions
static void	geoMagInit (void)

int	geoMag (double alt, double glat, double glon, double time, double dec, double dip, double ti, double gv, double adec, double adip, double ati, double x, double y, double z, double h, double ax, double ay, double az, double *ah)
	This routine computes all of the relevant geomagnetic data. More...

int	geomg1 (double alt, double glat, double glon, double time, double dec, double dip, double ti, double gv)

int	geoMagGetDec (double lat, double lon, double hgt, int month, int day, int year, double *dec)
	This routine computes magnetic declination. More...

double	geoMagGetDecRet (double lat, double lon, double hgt, int month, int day, int year)
	This routine computes and returns magnetic declination for a specific date. More...

double	geoMagGetDecNow (double lat, double lon, double hgt)
	This routine computes magnetic declination for now time. More...

int	geoMagFillDec (GEO_LOCATION l, double dec)

Variables
static WMM_DATA	wmmDta2000 []
	This structure array contains the all of the coefficients for WMM-2000 used in this library. More...

static WMM_DATA	wmmDta2005 []
	This structure array contains the all of the coefficients for WMM-2005 used in this library. More...

static WMM_DATA	wmmDta2010 []

static int	started = 0

static double	c [13][13]
	C - GAUSS COEFFICIENTS OF MAIN GEOMAGNETIC MODEL (NT) More...

static double	cd [13][13]
	CD - GAUSS COEFFICIENTS OF SECULAR GEOMAGNETIC MODEL (NT/YR) More...

static double	tc [13][13]
	TC - TIME ADJUSTED GEOMAGNETIC GAUSS COEFFICIENTS (NT) More...

static double	dp [13][13]
	DP(N,M)- THETA DERIVATIVE OF P(N,M) (UNNORMALIZED) More...

static double	p [13][13]
	SNORM - SCHMIDT NORMALIZATION FACTORS. More...

static double	sp [13]
	SP(M) - SINE OF (M*SPHERICAL COORD. LONGITUDE) More...

static double	cp [13]
	CP(M) - COSINE OF (M*SPHERICAL COORD. LONGITUDE) More...

static double	fn [13]

static double	fm [13]

static double	pp [13]
	PP(N) - ASSOCIATED LEGENDRE POLYNOMIALS FOR M=1 (UNNORMALIZED) More...

static double	k [13][13]

static double	epoch

static int	maxord
	MAXORD - MAXIMUM ORDER OF SPHERICAL HARMONIC MODEL. More...

Detailed Description

This file contains the source for deriving geomagnetic variables from geodetic coordinates.

Definition in file geoMag.c.

Macro Definition Documentation

#define EPOCH 2010.0

Definition at line 15 of file geoMag.c.

Referenced by geoMagInit().

#define MAXDEG 12

Definition at line 395 of file geoMag.c.

Referenced by geoMagInit().

#define snorm p

Flag for limiting multiple initializations

Definition at line 394 of file geoMag.c.

Referenced by geoMagInit().

#define wmmData wmmDta2010

Definition at line 14 of file geoMag.c.

Referenced by geoMagInit().

Function Documentation

int geoMag	(	double	alt,
		double	glat,
		double	glon,
		double	time,
		double *	dec,
		double *	dip,
		double *	ti,
		double *	gv,
		double *	adec,
		double *	adip,
		double *	ati,
		double *	x,
		double *	y,
		double *	z,
		double *	h,
		double *	ax,
		double *	ay,
		double *	az,
		double *	ah
	)

This routine computes all of the relevant geomagnetic data.

Parameters

double	alt : in: altitude in meters
double	glat : in: latitude in decimal degrees
double	glon : in: longitude in decimal degrees
double	time : in: time in decimal years
double	*dec :out: declination in degrees
double	*dip :out: dip in degrees
double	*ti :out: total intensity in nT
double	*gv :out: geomagnetic grid variation
double	*adec :out: Annual declination in degrees
double	*adip :out: Annual dip in degrees
double	*ati :out: Annual total intensity in nT
double	*x :out: X Component of the magnetic field
double	*y :out: Y Component of the magnetic field
double	*z :out: Z Component of the magnetic field
double	*h :out: h Component of the magnetic field
double	*ax :out: Annual X Component of the magnetic field
double	*ay :out: Annual Y Component of the magnetic field
double	*az :out: Annual Z Component of the magnetic field
double	*ah :out: Annual H Component of the magnetic field

Return values

GEO_OK	on success
GEO_ERROR	on error

{

Definition at line 523 of file geoMag.c.

References DEG_TO_MIN, DEG_TO_RAD, GEO_OK, geoMagInit(), and geomg1().

 {
     double time1;
     double dec2, dip2, ti2, rdec, rdip, rdec2, rdip2;
     double x2,y2,z2,h2;
     double c_rdip,c_rdip2;
     //    double rTd=0.017453292;
 
     geoMagInit();
 
     geomg1(alt,glat,glon,time,dec,dip,ti,gv);
     time1 = time + 1.0; // add a year to time
     geomg1(alt,glat,glon,time1,&dec2,&dip2,&ti2,gv);
 
 
 
     /*COMPUTE X, Y, Z, AND H COMPONENTS OF THE MAGNETIC FIELD*/
     rdec = *dec  * DEG_TO_RAD;
     rdip = *dip  * DEG_TO_RAD;
     rdec2 = dec2 * DEG_TO_RAD;
     rdip2 = dip2 * DEG_TO_RAD;
     c_rdip  = cos(rdip);
     c_rdip2 = cos(rdip2);
     /*
       *x= *ti * (cos(rdec) * cos(rdip));
       *y= *ti * (cos(rdip) * sin(rdec));
       *z= *ti * (sin(rdip));
       *h= *ti * (cos(rdip));
 
       x2=ti2*(cos(rdec2) * cos(rdip2));
       y2=ti2*(cos(rdip2) * sin(rdec2));
       z2=ti2*(sin(rdip2));
       h2=ti2*(cos(rdip2));
 */
     *x= *ti * (cos(rdec) * c_rdip);
     *y= *ti * (c_rdip    * sin(rdec));
     *z= *ti * (sin(rdip));
     *h= *ti * (c_rdip);
 
     x2=ti2*(cos(rdec2) * c_rdip2);
     y2=ti2*(c_rdip2    * sin(rdec2));
     z2=ti2*(sin(rdip2));
     h2=ti2*(c_rdip2);
 
 
     /*  COMPUTE ANNUAL CHANGE FOR TOTAL INTENSITY  */
     *ati = ti2 - *ti;
 
     /*  COMPUTE ANNUAL CHANGE FOR DIP & DEC (in minutes) */
     *adip = (dip2 - *dip) * DEG_TO_MIN;
     *adec = (dec2 - *dec) * DEG_TO_MIN;
 
 
     /*  COMPUTE ANNUAL CHANGE FOR X, Y, Z, AND H */
     *ax  = x2 - *x;
     *ay  = y2 - *y;
     *az  = z2 - *z;
     *ah  = h2 - *h;
 
     return(GEO_OK);
 }

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int geoMagFillDec	(	GEO_LOCATION *	l,
		double *	dec
	)

Definition at line 903 of file geoMag.c.

References GEO_LOCATION::Declination, GEO_OK, geoMagGetDec(), GEO_LOCATION::hgt, GEO_LOCATION::lat, and GEO_LOCATION::lon.

Referenced by geoInitLocation().

 {
     struct tm *newtime;
     time_t aclock;
 
     /* Compute the Magnetic Declination */
     time( &aclock );                 /* Get time in seconds */
     newtime = localtime( &aclock );  /* Convert time to struct tm form */
 
     if(newtime->tm_year < 200 ) newtime->tm_year += 1900;
 
     //   printf("%d / %d / %d \n",newtime->tm_mon+1, newtime->tm_mday, newtime->tm_year);
     geoMagGetDec(l->lat,l->lon,l->hgt,
     newtime->tm_mon+1, newtime->tm_mday, newtime->tm_year, dec);
     l->Declination = *dec;
 
     return (GEO_OK);
 }

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int geoMagGetDec	(	double	lat,
		double	lon,
		double	hgt,
		int	month,
		int	day,
		int	year,
		double *	dec
	)

This routine computes magnetic declination.

Parameters

double	lat : in: latitude in decimal degrees
double	lon : in: longitude in decimal degrees
double	hgt : in: altitude in meters
int	month : in: Month of the year
int	day : in: Day of the month
int	year : in: Year
double	dec :out: declination in degrees

Definition at line 825 of file geoMag.c.

References GEO_OK, geoMagInit(), geomg1(), and jday().

Referenced by geoMagFillDec(), and geoMagGetDecNow().

 {
     /* Days in each month 1-12 */
     int jday[] = {0,0,31,59,90,120,151,180,211,242,272,303,333 };
     double time,dip,ti,gv;
 
     /* Determin decimal years from date */
     time = ((jday[month]+day) / 365.0) + year;
 
     /* Determin declination */
     geoMagInit();
     geomg1(hgt,lat,lon,time,dec,&dip,&ti,&gv);
 
     return (GEO_OK);
 
 }

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double geoMagGetDecNow	(	double	lat,
		double	lon,
		double	hgt
	)

This routine computes magnetic declination for now time.

Parameters

double	lat : in: latitude in decimal degrees
double	lon : in: longitude in decimal degrees
double	hgt : in: altitude in meters

Return values

double dec :out: declination in degrees

Definition at line 882 of file geoMag.c.

References geoMagGetDec().

 {
     struct tm *newtime;
     time_t aclock;
     double dec;
 
     /* Compute the Magnetic Declination */
     time( &aclock );                 /* Get time in seconds */
     newtime = localtime( &aclock );  /* Convert time to struct tm form */
 
     if(newtime->tm_year < 200 ) newtime->tm_year += 1900;
 
     //   printf("%d / %d / %d \n",newtime->tm_mon+1, newtime->tm_mday, newtime->tm_year);
     geoMagGetDec(lat,lon,hgt,
     newtime->tm_mon+1, newtime->tm_mday, newtime->tm_year, &dec);
 
     return (dec);
 
 }

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double geoMagGetDecRet	(	double	lat,
		double	lon,
		double	hgt,
		int	month,
		int	day,
		int	year
	)

This routine computes and returns magnetic declination for a specific date.

Parameters

double	lat : in: latitude in decimal degrees
double	lon : in: longitude in decimal degrees
double	hgt : in: altitude in meters
int	month : in: Month of the year
int	day : in: Day of the month
int	year : in: Year

Return values

double dec :out: declination in degrees

Definition at line 855 of file geoMag.c.

References geoMagInit(), geomg1(), and jday().

 {
     /* Days in each month 1-12 */
     double dec;
     int jday[] = {0,0,31,59,90,120,151,180,211,242,272,303,333 };
     double time,dip,ti,gv;
 
     /* Determin decimal years from date */
     time = ((jday[month]+day) / 365.0) + year;
 
     /* Determin declination */
     geoMagInit();
     geomg1(hgt,lat,lon,time,&dec,&dip,&ti,&gv);
 
     return (dec);
 
 }

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static void geoMagInit ( void )

static

Definition at line 424 of file geoMag.c.

References c, cd, cp, dp, EPOCH, epoch, fm, fn, k, MAXDEG, maxord, n(), p, pp, snorm, sp, started, and wmmData.

Referenced by geoMag(), geoMagGetDec(), and geoMagGetDecRet().

 {
     int n,m,i,j;
     double flnmj,n2m1,nm12,n2m1stuff;
 
     /* Only do this once */
     if(started) return;
     started = 1;
 
     // INITIALIZE CONSTANTS
     maxord = MAXDEG;
     sp[0] = 0.0;
     cp[0] = p[0][0] = pp[0] = 1.0;
     dp[0][0] = 0.0;
 
     // READ WORLD MAGNETIC MODEL SPHERICAL HARMONIC COEFFICIENTS
     c[0][0]  = 0.0;
     cd[0][0] = 0.0;
 
     // Load the WMM Coefficients
     epoch=EPOCH;
     for( i=0;i<90;i++)
     {
         n=wmmData[i].n;
         m=wmmData[i].m;
         if (m <= n)
         {
             c[m][n] = wmmData[i].gnm;
             cd[m][n] = wmmData[i].dgnm;
             if (m != 0)
             {
                 c[n][m-1] = wmmData[i].hnm;
                 cd[n][m-1] = wmmData[i].dhnm;
             }
         }
     } //end for
 
 
     /* CONVERT SCHMIDT NORMALIZED GAUSS COEFFICIENTS TO UNNORMALIZED */
 
     snorm[0][0] = 1.0;
     for (n=1; n<=maxord; n++)
     {
         nm12 = (n-1)*(n-1);
         n2m1 = (double)2*n-1;
         n2m1stuff = (double)(n2m1*(2*n-3));
         snorm[0][n] = snorm[0][n-1]*n2m1/(double)n;
         j = 2;
         for (m=0;m<=n;m++)
         {
             k[m][n] = (double)(nm12-(m*m))/n2m1stuff;
             if (m > 0)
             {
                 flnmj = (double)((n-m+1)*j)/(double)(n+m);
                 snorm[m][n] = snorm[m-1][n]*sqrt(flnmj);
                 j = 1;
                 c[n][m-1] = snorm[m][n]*c[n][m-1];
                 cd[n][m-1] = snorm[m][n]*cd[n][m-1];
             }
             c[m][n] = snorm[m][n]*c[m][n];
             cd[m][n] = snorm[m][n]*cd[m][n];
         } //end for m
         fn[n] = (double)(n+1);
         fm[n] = (double)n;
     } //end for n
     k[1][1] = 0.0;
 
 
 }

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int geomg1	(	double	alt,
		double	glat,
		double	glon,
		double	time,
		double *	dec,
		double *	dip,
		double *	ti,
		double *	gv
	)

This is documentation that came with the WMM. It is included here for completeness.

//       MAXDEG - MAXIMUM DEGREE OF SPHERICAL HARMONIC MODEL    (INPUT)
//       TIME   - COMPUTATION TIME (YRS)                        (INPUT)
//                (EG. 1 JULY 1995 = 1995.500)
//       ALT    - GEODETIC ALTITUDE (M)                        (INPUT)
//       GLAT   - GEODETIC LATITUDE (DEG.)                      (INPUT)
//       GLON   - GEODETIC LONGITUDE (DEG.)                     (INPUT)
//       EPOCH  - BASE TIME OF GEOMAGNETIC MODEL (YRS)
//       P(N,M) - ASSOCIATED LEGENDRE POLYNOMIALS (UNNORMALIZED)
//       DEC    - GEOMAGNETIC DECLINATION (DEG.)                (OUTPUT)
//                  EAST=POSITIVE ANGLES
//                  WEST=NEGATIVE ANGLES
//       DIP    - GEOMAGNETIC INCLINATION (DEG.)                (OUTPUT)
//                  DOWN=POSITIVE ANGLES
//                    UP=NEGATIVE ANGLES
//       TI     - GEOMAGNETIC TOTAL INTENSITY (NT)              (OUTPUT)
//       GV     - GEOMAGNETIC GRID VARIATION (DEG.)             (OUTPUT)
//                REFERENCED TO GRID NORTH
//                GRID NORTH REFERENCED TO 0 MERIDIAN
//                OF A POLAR STEREOGRAPHIC PROJECTION
//                (ARCTIC/ANTARCTIC ONLY)
//       A      - SEMIMAJOR AXIS OF WGS-84 ELLIPSOID (KM)
//       B      - SEMIMINOR AXIS OF WGS-84 ELLIPSOID (KM)
//       RE     - MEAN RADIUS OF IAU-66 ELLIPSOID (KM)
//       a2,             // a * a
//       b2,             // b * b
//       c2,             // a2 - b2
//       a4,             // a2 * a2
//       b4,             // b2 * b2
//       c4,             // a4 - b4
//       ct,             //C       CT     - COSINE OF (SPHERICAL COORD. LATITUDE)
//       st,             //C       ST     - SINE OF (SPHERICAL COORD. LATITUDE)
//       r2,
//       r,              //C       R      - SPHERICAL COORDINATE RADIAL POSITION (KM)
//       ca,             //C       CA     - COSINE OF SPHERICAL TO GEODETIC VECTOR ROTATION ANGLE
//       sa,             //C       SA     - SINE OF SPHERICAL TO GEODETIC VECTOR ROTATION ANGLE
//       br,             //C       BR     - RADIAL COMPONENT OF GEOMAGNETIC FIELD (NT)
//       bt,             //C       BT     - THETA COMPONENT OF GEOMAGNETIC FIELD (NT)
//       bp,             //C       BP     - PHI COMPONENT OF GEOMAGNETIC FIELD (NT)
//       bx,             //C       BX     - NORTH GEOMAGNETIC COMPONENT (NT)
//       by,             //C       BY     - EAST GEOMAGNETIC COMPONENT (NT)
//       bz,             //C       BZ     - VERTICALLY DOWN GEOMAGNETIC COMPONENT (NT)
//       bh;             //C       BH     - HORIZONTAL GEOMAGNETIC COMPONENT (NT)

Definition at line 595 of file geoMag.c.

References GEO_ELLIPSOID::a, c, cd, CIRCLE, cp, DEG_TO_RAD, dp, ellips, epoch, fm, fn, GEO_B, GEO_DATUM_WE, GEO_OK, HALF_CIRCLE, k, maxord, n(), p, pp, RAD_TO_DEG, sp, and tc.

Referenced by geoMag(), geoMagGetDec(), and geoMagGetDecRet().

 {
 
     /*!
 This is documentation that came with the WMM. It is included here for completeness.
 \verbatim
 //       MAXDEG - MAXIMUM DEGREE OF SPHERICAL HARMONIC MODEL    (INPUT)
 //       TIME   - COMPUTATION TIME (YRS)                        (INPUT)
 //                (EG. 1 JULY 1995 = 1995.500)
 //       ALT    - GEODETIC ALTITUDE (M)                        (INPUT)
 //       GLAT   - GEODETIC LATITUDE (DEG.)                      (INPUT)
 //       GLON   - GEODETIC LONGITUDE (DEG.)                     (INPUT)
 //       EPOCH  - BASE TIME OF GEOMAGNETIC MODEL (YRS)
 //       P(N,M) - ASSOCIATED LEGENDRE POLYNOMIALS (UNNORMALIZED)
 //       DEC    - GEOMAGNETIC DECLINATION (DEG.)                (OUTPUT)
 //                  EAST=POSITIVE ANGLES
 //                  WEST=NEGATIVE ANGLES
 //       DIP    - GEOMAGNETIC INCLINATION (DEG.)                (OUTPUT)
 //                  DOWN=POSITIVE ANGLES
 //                    UP=NEGATIVE ANGLES
 //       TI     - GEOMAGNETIC TOTAL INTENSITY (NT)              (OUTPUT)
 //       GV     - GEOMAGNETIC GRID VARIATION (DEG.)             (OUTPUT)
 //                REFERENCED TO GRID NORTH
 //                GRID NORTH REFERENCED TO 0 MERIDIAN
 //                OF A POLAR STEREOGRAPHIC PROJECTION
 //                (ARCTIC/ANTARCTIC ONLY)
 //       A      - SEMIMAJOR AXIS OF WGS-84 ELLIPSOID (KM)
 //       B      - SEMIMINOR AXIS OF WGS-84 ELLIPSOID (KM)
 //       RE     - MEAN RADIUS OF IAU-66 ELLIPSOID (KM)
 //       a2,             // a * a
 //       b2,             // b * b
 //       c2,             // a2 - b2
 //       a4,             // a2 * a2
 //       b4,             // b2 * b2
 //       c4,             // a4 - b4
 //       ct,             //C       CT     - COSINE OF (SPHERICAL COORD. LATITUDE)
 //       st,             //C       ST     - SINE OF (SPHERICAL COORD. LATITUDE)
 //       r2,
 //       r,              //C       R      - SPHERICAL COORDINATE RADIAL POSITION (KM)
 //       ca,             //C       CA     - COSINE OF SPHERICAL TO GEODETIC VECTOR ROTATION ANGLE
 //       sa,             //C       SA     - SINE OF SPHERICAL TO GEODETIC VECTOR ROTATION ANGLE
 //       br,             //C       BR     - RADIAL COMPONENT OF GEOMAGNETIC FIELD (NT)
 //       bt,             //C       BT     - THETA COMPONENT OF GEOMAGNETIC FIELD (NT)
 //       bp,             //C       BP     - PHI COMPONENT OF GEOMAGNETIC FIELD (NT)
 //       bx,             //C       BX     - NORTH GEOMAGNETIC COMPONENT (NT)
 //       by,             //C       BY     - EAST GEOMAGNETIC COMPONENT (NT)
 //       bz,             //C       BZ     - VERTICALLY DOWN GEOMAGNETIC COMPONENT (NT)
 //       bh;             //C       BH     - HORIZONTAL GEOMAGNETIC COMPONENT (NT)
 \endverbatim
 */
 
     int m,n;
     double temp1, temp2,d,ar,aor,dt,bpp,
     par, parp,r,r2,sa,ca,st,ct,br,bt,bp,bx,by,bz,bh;
 
     double               rlon,rlat,
     srlon, srlat, crlon, crlat,
     srlat2, crlat2,
     a,              //       A      - SEMIMAJOR AXIS OF WGS-84 ELLIPSOID (KM)
     b,              //       B      - SEMIMINOR AXIS OF WGS-84 ELLIPSOID (KM)
     re,             //       RE     - MEAN RADIUS OF IAU-66 ELLIPSOID (KM)
     a2,             //   a * a
     b2,             //   b * b
     c2,             //   a2 - b2
     a4,             //   a2 * a2
     b4,             //   b2 * b2
     c4,             //   a4 - b4
 
     q, q1, q2;
 
     a = ellips[GEO_DATUM_WE].a; //6378137.0;
     b = GEO_B(ellips[GEO_DATUM_WE].a, (ellips[GEO_DATUM_WE].f1)); //6356752.3142; //wgs-84
     re = 6371200.0;
     a2 = a*a;
     b2 = b*b;
     c2 = a2-b2;
     a4 = a2*a2;
     b4 = b2*b2;
     c4 = a4 - b4;
 
 
     dt = time - epoch;
     //     if (dt < 0.0 || dt > 5.0)
     //                  printf("\n WARNING geoMag - TIME EXTENDS BEYOND MODEL 5-YEAR LIFE SPAN (dt=%f, time=%f)\n",dt,time);
 
     rlon   = glon*DEG_TO_RAD;
     rlat   = glat*DEG_TO_RAD;
     srlon  = sin(rlon);
     srlat  = sin(rlat);
     crlon  = cos(rlon);
     crlat  = cos(rlat);
     srlat2 = srlat*srlat;
     crlat2 = crlat*crlat;
     sp[1]  = srlon;
     cp[1]  = crlon;
 
     /* CONVERT FROM GEODETIC COORDS. TO SPHERICAL COORDS. */
 
     q = sqrt(a2-c2*srlat2);
     q1 = alt*q;
     q2 = ((q1+a2)/(q1+b2))*((q1+a2)/(q1+b2));
     ct = srlat/sqrt(q2*crlat2+srlat2);
     st = sqrt(1.0-(ct*ct));
     r2 = (alt*alt)+2.0*q1+(a4-c4*srlat2)/(q*q);
     r = sqrt(r2);
     d = sqrt(a2*crlat2+b2*srlat2);
     ca = (alt+d)/r;
     sa = c2*crlat*srlat/(r*d);
 
     for (m=2; m<=maxord; m++)
     {
         sp[m] = sp[1]*cp[m-1]+cp[1]*sp[m-1];
         cp[m] = cp[1]*cp[m-1]-sp[1]*sp[m-1];
     }
 
     aor = re/r;
     ar = aor*aor;
     br = bt = bp = bpp = 0.0;
     for (n=1; n<=maxord; n++)
     {
         ar = ar*aor;
         for (m=0;m<=n;m++)
         {
             /*
         COMPUTE UNNORMALIZED ASSOCIATED LEGENDRE POLYNOMIALS
         AND DERIVATIVES VIA RECURSION RELATIONS
      */
             if (n == m)
             {
                 p[m][n]  = st * p[m-1][n-1];
                 dp[m][n] = st * dp[m-1][n-1] + ct * p[m-1][n-1];
                 goto S50;
             }
             if (n == 1 && m == 0)
             {
                 p[m][n]  = ct * p[m][n-1];
                 dp[m][n] = ct * dp[m][n-1] - st * p[m][n-1];
                 goto S50;
             }
             if (n > 1 && n != m)
             {
                 if (m > n-2) p[m][n-2]  = 0.0;
                 if (m > n-2) dp[m][n-2] = 0.0;
                 p[m][n]  = ct * p[m][n-1]  - k[m][n] * p[m][n-2];
                 dp[m][n] = ct * dp[m][n-1] - st * p[m][n-1] - k[m][n] * dp[m][n-2];
             }
 S50:
             //  TIME ADJUST THE GAUSS COEFFICIENTS
             tc[m][n] = c[m][n]+dt*cd[m][n];
             if (m != 0) tc[n][m-1] = c[n][m-1]+dt*cd[n][m-1];
 
             // ACCUMULATE TERMS OF THE SPHERICAL HARMONIC EXPANSIONS
             par = ar * p[m][n];
             if (m == 0)
             {
                 temp1 = tc[m][n]*cp[m];
                 temp2 = tc[m][n]*sp[m];
             }
             else
             {
                 temp1 = tc[m][n]*cp[m]+tc[n][m-1]*sp[m];
                 temp2 = tc[m][n]*sp[m]-tc[n][m-1]*cp[m];
             }
             bt = bt-ar*temp1*dp[m][n];
             bp += (fm[m]*temp2*par);
             br += (fn[n]*temp1*par);
 
             //  SPECIAL CASE:  NORTH/SOUTH GEOGRAPHIC POLES
             if (st == 0.0 && m == 1)
             {
                 if (n == 1) pp[n] = pp[n-1];
                 else pp[n] = ct*pp[n-1]-k[m][n]*pp[n-2];
                 parp = ar*pp[n];
                 bpp += (fm[m]*temp2*parp);
             }
         }
     }
     if (st == 0.0) bp = bpp;
     else bp /= st;
     /*
     ROTATE MAGNETIC VECTOR COMPONENTS FROM SPHERICAL TO
     GEODETIC COORDINATES
 */
     bx = -bt*ca-br*sa;
     by = bp;
     bz = bt*sa-br*ca;
     /*
 **    COMPUTE DECLINATION (DEC), INCLINATION (DIP) AND
 **    TOTAL INTENSITY (TI)
 */
     bh   = sqrt((bx*bx)+(by*by));
     *ti  = sqrt((bh*bh)+(bz*bz));
     *dec = atan2(by,bx)*RAD_TO_DEG;
     *dip = atan2(bz,bh)*RAD_TO_DEG;
 
     /*
 **    COMPUTE MAGNETIC GRID VARIATION IF THE CURRENT
 **    GEODETIC POSITION IS IN THE ARCTIC OR ANTARCTIC
 **    (I.E. GLAT > +55 DEGREES OR GLAT < -55 DEGREES)
 **
 **    OTHERWISE, SET MAGNETIC GRID VARIATION TO -999.0
 */
     *gv = -999.0;
     if (fabs(glat) >= 55.)
     {
         if (glat > 0.0 && glon >= 0.0)  *gv = *dec-glon;
         if (glat > 0.0 && glon < 0.0)   *gv = *dec+fabs(glon);
         if (glat < 0.0 && glon >= 0.0)  *gv = *dec+glon;
         if (glat < 0.0 && glon < 0.0)   *gv = *dec-fabs(glon);
         if (*gv > +HALF_CIRCLE) *gv -= CIRCLE;
         if (*gv < -HALF_CIRCLE) *gv += CIRCLE;
     }
 
     return (GEO_OK);
 
 }

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Variable Documentation

double c[13][13]

static

C - GAUSS COEFFICIENTS OF MAIN GEOMAGNETIC MODEL (NT)

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), geomg1(), and geoSunAA().

double cd[13][13]

static

CD - GAUSS COEFFICIENTS OF SECULAR GEOMAGNETIC MODEL (NT/YR)

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double cp[13]

static

CP(M) - COSINE OF (M*SPHERICAL COORD. LONGITUDE)

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double dp[13][13]

static

DP(N,M)- THETA DERIVATIVE OF P(N,M) (UNNORMALIZED)

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double epoch

static

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double fm[13]

static

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double fn[13]

static

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double k[13][13]

static

Definition at line 404 of file geoMag.c.

Referenced by geoEfg2Llh_vermeille(), geoEfg2Llh_vermeille_fast(), geoMagInit(), and geomg1().

int maxord

static

MAXORD - MAXIMUM ORDER OF SPHERICAL HARMONIC MODEL.

Definition at line 420 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double p[13][13]

static

SNORM - SCHMIDT NORMALIZATION FACTORS.

Definition at line 404 of file geoMag.c.

Referenced by geoEfg2Llh(), geoEfg2Llh_aa(), geoEfg2Llh_aa_fast(), geoEfg2Llh_borkowski(), geoEfg2Llh_borkowski_fast(), geoEfg2Llh_bowring(), geoEfg2Llh_bowring_fast(), geoEfg2Llh_fast(), geoEfg2Llh_heikkinen(), geoEfg2Llh_hm(), geoEfg2Llh_hm_fast(), geoEfg2Llh_torge(), geoEfg2Llh_torge_fast(), geoEfg2Llh_vermeille(), geoEfg2Llh_vermeille_fast(), geoMagInit(), and geomg1().

double pp[13]

static

PP(N) - ASSOCIATED LEGENDRE POLYNOMIALS FOR M=1 (UNNORMALIZED)

Definition at line 404 of file geoMag.c.

Referenced by geoMagInit(), and geomg1().

double sp[13]

static

SP(M) - SINE OF (M*SPHERICAL COORD. LONGITUDE)

Definition at line 404 of file geoMag.c.

Referenced by geoEfg2Llh_heikkinen(), geoMagInit(), and geomg1().

int started = 0

static

Definition at line 392 of file geoMag.c.

Referenced by geoMagInit().

double tc[13][13]

static

TC - TIME ADJUSTED GEOMAGNETIC GAUSS COEFFICIENTS (NT)

Definition at line 404 of file geoMag.c.

Referenced by geomg1().

WMM_DATA wmmDta2000[]

static

This structure array contains the all of the coefficients for WMM-2000 used in this library.

This is documentation that came with the WMM. It is included here for completeness.

C     MODEL:  THE WMM SERIES GEOMAGNETIC MODELS ARE COMPOSED
C             OF TWO PARTS:  THE MAIN FIELD MODEL, WHICH IS
C             VALID AT THE BASE EPOCH OF THE CURRENT MODEL AND
C             A SECULAR VARIATION MODEL, WHICH ACCOUNTS FOR SLOW
C             TEMPORAL VARIATIONS IN THE MAIN GEOMAGNETIC FIELD
C             FROM THE BASE EPOCH TO A MAXIMUM OF 5 YEARS BEYOND
C             THE BASE EPOCH.  FOR EXAMPLE, THE BASE EPOCH OF
C             THE WMM-2005 MODEL IS 2005.0.  THIS MODEL IS THEREFORE
C             CONSIDERED VALID BETWEEN 2005.0 AND 2010.0. THE
C             COMPUTED MAGNETIC PARAMETERS ARE REFERENCED TO THE
C             WGS-84 ELLIPSOID.
C
C***********************************************************************
C
C     ACCURACY:  IN OCEAN AREAS AT THE EARTH'S SURFACE OVER THE
C                ENTIRE 5 YEAR LIFE OF THE DEGREE AND ORDER 12
C                SPHERICAL HARMONIC MODEL WMM-2005, THE ESTIMATED
C                MAXIMUM RMS ERRORS FOR THE VARIOUS MAGNETIC COMPONENTS
C                ARE:
C
C                DEC  -   0.5 Degrees
C                DIP  -   0.5 Degrees
C                TI   - 280.0 nanoTeslas (nT)
C                GV   -   0.5 Degrees
C
C                OTHER MAGNETIC COMPONENTS THAT CAN BE DERIVED FROM
C                THESE FOUR BY SIMPLE TRIGONOMETRIC RELATIONS WILL
C                HAVE THE FOLLOWING APPROXIMATE ERRORS OVER OCEAN AREAS:
C
C                X    - 140 nT (North)
C                Y    - 140 nT (East)
C                Z    - 200 nT (Vertical) Positive is down
C                H    - 200 nT (Horizontal)
C
C                OVER LAND THE MAXIMUM RMS ERRORS ARE EXPECTED TO BE
C                HIGHER, ALTHOUGH THE RMS ERRORS FOR DEC, DIP, AND GV
C                ARE STILL ESTIMATED TO BE LESS THAN 1.0 DEGREE, FOR
C                THE ENTIRE 5-YEAR LIFE OF THE MODEL AT THE EARTH's
C                SURFACE.  THE OTHER COMPONENT ERRORS OVER LAND ARE
C                MORE DIFFICULT TO ESTIMATE AND SO ARE NOT GIVEN.
C
C                THE ACCURACY AT ANY GIVEN TIME FOR ALL OF THESE
C                GEOMAGNETIC PARAMETERS DEPENDS ON THE GEOMAGNETIC
C                LATITUDE.  THE ERRORS ARE LEAST FROM THE EQUATOR TO
C                MID-LATITUDES AND GREATEST NEAR THE MAGNETIC POLES.
C
C                IT IS VERY IMPORTANT TO NOTE THAT A DEGREE AND
C                ORDER 12 MODEL, SUCH AS WMM-2005, DESCRIBES ONLY
C                THE LONG WAVELENGTH SPATIAL MAGNETIC FLUCTUATIONS
C                DUE TO EARTH'S CORE.  NOT INCLUDED IN THE WMM SERIES
C                MODELS ARE INTERMEDIATE AND SHORT WAVELENGTH
C                SPATIAL FLUCTUATIONS OF THE GEOMAGNETIC FIELD
C                WHICH ORIGINATE IN THE EARTH'S MANTLE AND CRUST.
C                CONSEQUENTLY, ISOLATED ANGULAR ERRORS AT VARIOUS
C                POSITIONS ON THE SURFACE (PRIMARILY OVER LAND, IN
C                CONTINENTAL MARGINS AND OVER OCEANIC SEAMOUNTS,
C                RIDGES AND TRENCHES) OF SEVERAL DEGREES MAY BE
C                EXPECTED. ALSO NOT INCLUDED IN THE MODEL ARE
C                NONSECULAR TEMPORAL FLUCTUATIONS OF THE GEOMAGNETIC
C                FIELD OF MAGNETOSPHERIC AND IONOSPHERIC ORIGIN.
C                DURING MAGNETIC STORMS, TEMPORAL FLUCTUATIONS CAN
C                CAUSE SUBSTANTIAL DEVIATIONS OF THE GEOMAGNETIC
C                FIELD FROM MODEL VALUES.  IN ARCTIC AND ANTARCTIC
C                REGIONS, AS WELL AS IN EQUATORIAL REGIONS, DEVIATIONS
C                FROM MODEL VALUES ARE BOTH FREQUENT AND PERSISTENT.
C
C                IF THE REQUIRED DECLINATION ACCURACY IS MORE
C                STRINGENT THAN THE WMM SERIES OF MODELS PROVIDE, THEN
C                THE USER IS ADVISED TO REQUEST SPECIAL (REGIONAL OR
C                LOCAL) SURVEYS BE PERFORMED AND MODELS PREPARED.
C                REQUESTS OF THIS NATURE SHOULD BE MADE TO NIMA
C                AT THE ADDRESS ABOVE.

Definition at line 98 of file geoMag.c.

WMM_DATA wmmDta2005[]

static

This structure array contains the all of the coefficients for WMM-2005 used in this library.

Definition at line 199 of file geoMag.c.

WMM_DATA wmmDta2010[]

static

Definition at line 297 of file geoMag.c.

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