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geomag.c
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// March 2020: Made to work as a small and easy to use library for GNU/Linux C programs by M. Wirth
// Original notes provided below
/* PROGRAM MAGPOINT (GEOMAG DRIVER) */
/************************************************************************
Contact Information
Software and Model Support
National Geophysical Data Center
NOAA EGC/2
325 Broadway
Boulder, CO 80303 USA
Attn: Manoj Nair or Stefan Maus
Phone: (303) 497-4642 or -6522
Email: [email protected] or [email protected]
Web: http://www.ngdc.noaa.gov/geomag/WMM/
Sponsoring Government Agency
National Geospatial-Intelligence Agency
PRG / CSAT, M.S. L-41
3838 Vogel Road
Arnold, MO 63010
Attn: Craig Rollins
Phone: (314) 263-4186
Email: [email protected]
Original Program By:
Dr. John Quinn
FLEET PRODUCTS DIVISION, CODE N342
NAVAL OCEANOGRAPHIC OFFICE (NAVOCEANO)
STENNIS SPACE CENTER (SSC), MS 39522-5001
3/25/05 Version 2.0 Stefan Maus corrected 2 bugs:
- use %c instead of %s for character read
- help text: positive inclination is downward
1/29/2010 Version 3.0 Manoj Nair
Converted floating variables from single precision to double
Changed : height above AMSL (WGS84) to Height above WGS84 Ellipsoid
Removed the NaN forcing at the geographic poles
A new function "my_isnan" for improved portablility
*/
// Copyright Notice
//
// As required by 17 U.S.C. 403, third parties producing copyrighted works
// consisting predominantly of the material produced by U.S. government agencies
// must provide notice with such work(s) identifying the U.S. Government material
// incorporated and stating that such material is not subject to copyright
// protection within the United States. The information on government web pages
// is in the public domain and not subject to copyright protection within the
// United States unless specifically annotated otherwise (copyright may be held
// elsewhere). Foreign copyrights may apply.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#define NaN log(-1.0)
static char **wmm_lines;
static char *wmm_string;
static int wmm_index;
static int maxdeg;
static double epochlowlim,epochuplim,epoch;
char decd[7], dipd[7],modl[20];
static char* goodbye = "\n -- End of WMM Point Calculation Program -- \n\n";
static int my_isnan(double d)
{
return (d != d); /* IEEE: only NaN is not equal to itself */
}
static int geomag_E0_init(int *maxdeg);
static char geomag_introduction(double epochlowlim);
int geomag_destroy() {
return 0;
}
int geomag_init()
{
// hard code WMM2020, this can easily enough be replaced
// i don't like having to read a file, better to have the data in the source code.
// when replacing this, make sure to add \n\ at the end of each line to the text from the WMM.COF
// also make sure the indentation stays as it is ... some code depends on that.
wmm_string = strdup("\
2020.0 WMM-2020 12/10/2019\n\
1 0 -29404.5 0.0 6.7 0.0\n\
1 1 -1450.7 4652.9 7.7 -25.1\n\
2 0 -2500.0 0.0 -11.5 0.0\n\
2 1 2982.0 -2991.6 -7.1 -30.2\n\
2 2 1676.8 -734.8 -2.2 -23.9\n\
3 0 1363.9 0.0 2.8 0.0\n\
3 1 -2381.0 -82.2 -6.2 5.7\n\
3 2 1236.2 241.8 3.4 -1.0\n\
3 3 525.7 -542.9 -12.2 1.1\n\
4 0 903.1 0.0 -1.1 0.0\n\
4 1 809.4 282.0 -1.6 0.2\n\
4 2 86.2 -158.4 -6.0 6.9\n\
4 3 -309.4 199.8 5.4 3.7\n\
4 4 47.9 -350.1 -5.5 -5.6\n\
5 0 -234.4 0.0 -0.3 0.0\n\
5 1 363.1 47.7 0.6 0.1\n\
5 2 187.8 208.4 -0.7 2.5\n\
5 3 -140.7 -121.3 0.1 -0.9\n\
5 4 -151.2 32.2 1.2 3.0\n\
5 5 13.7 99.1 1.0 0.5\n\
6 0 65.9 0.0 -0.6 0.0\n\
6 1 65.6 -19.1 -0.4 0.1\n\
6 2 73.0 25.0 0.5 -1.8\n\
6 3 -121.5 52.7 1.4 -1.4\n\
6 4 -36.2 -64.4 -1.4 0.9\n\
6 5 13.5 9.0 -0.0 0.1\n\
6 6 -64.7 68.1 0.8 1.0\n\
7 0 80.6 0.0 -0.1 0.0\n\
7 1 -76.8 -51.4 -0.3 0.5\n\
7 2 -8.3 -16.8 -0.1 0.6\n\
7 3 56.5 2.3 0.7 -0.7\n\
7 4 15.8 23.5 0.2 -0.2\n\
7 5 6.4 -2.2 -0.5 -1.2\n\
7 6 -7.2 -27.2 -0.8 0.2\n\
7 7 9.8 -1.9 1.0 0.3\n\
8 0 23.6 0.0 -0.1 0.0\n\
8 1 9.8 8.4 0.1 -0.3\n\
8 2 -17.5 -15.3 -0.1 0.7\n\
8 3 -0.4 12.8 0.5 -0.2\n\
8 4 -21.1 -11.8 -0.1 0.5\n\
8 5 15.3 14.9 0.4 -0.3\n\
8 6 13.7 3.6 0.5 -0.5\n\
8 7 -16.5 -6.9 0.0 0.4\n\
8 8 -0.3 2.8 0.4 0.1\n\
9 0 5.0 0.0 -0.1 0.0\n\
9 1 8.2 -23.3 -0.2 -0.3\n\
9 2 2.9 11.1 -0.0 0.2\n\
9 3 -1.4 9.8 0.4 -0.4\n\
9 4 -1.1 -5.1 -0.3 0.4\n\
9 5 -13.3 -6.2 -0.0 0.1\n\
9 6 1.1 7.8 0.3 -0.0\n\
9 7 8.9 0.4 -0.0 -0.2\n\
9 8 -9.3 -1.5 -0.0 0.5\n\
9 9 -11.9 9.7 -0.4 0.2\n\
10 0 -1.9 0.0 0.0 0.0\n\
10 1 -6.2 3.4 -0.0 -0.0\n\
10 2 -0.1 -0.2 -0.0 0.1\n\
10 3 1.7 3.5 0.2 -0.3\n\
10 4 -0.9 4.8 -0.1 0.1\n\
10 5 0.6 -8.6 -0.2 -0.2\n\
10 6 -0.9 -0.1 -0.0 0.1\n\
10 7 1.9 -4.2 -0.1 -0.0\n\
10 8 1.4 -3.4 -0.2 -0.1\n\
10 9 -2.4 -0.1 -0.1 0.2\n\
10 10 -3.9 -8.8 -0.0 -0.0\n\
11 0 3.0 0.0 -0.0 0.0\n\
11 1 -1.4 -0.0 -0.1 -0.0\n\
11 2 -2.5 2.6 -0.0 0.1\n\
11 3 2.4 -0.5 0.0 0.0\n\
11 4 -0.9 -0.4 -0.0 0.2\n\
11 5 0.3 0.6 -0.1 -0.0\n\
11 6 -0.7 -0.2 0.0 0.0\n\
11 7 -0.1 -1.7 -0.0 0.1\n\
11 8 1.4 -1.6 -0.1 -0.0\n\
11 9 -0.6 -3.0 -0.1 -0.1\n\
11 10 0.2 -2.0 -0.1 0.0\n\
11 11 3.1 -2.6 -0.1 -0.0\n\
12 0 -2.0 0.0 0.0 0.0\n\
12 1 -0.1 -1.2 -0.0 -0.0\n\
12 2 0.5 0.5 -0.0 0.0\n\
12 3 1.3 1.3 0.0 -0.1\n\
12 4 -1.2 -1.8 -0.0 0.1\n\
12 5 0.7 0.1 -0.0 -0.0\n\
12 6 0.3 0.7 0.0 0.0\n\
12 7 0.5 -0.1 -0.0 -0.0\n\
12 8 -0.2 0.6 0.0 0.1\n\
12 9 -0.5 0.2 -0.0 -0.0\n\
12 10 0.1 -0.9 -0.0 -0.0\n\
12 11 -1.1 -0.0 -0.0 0.0\n\
12 12 -0.3 0.5 -0.1 -0.1\n\
999999999999999999999999999999999999999999999999\n\
999999999999999999999999999999999999999999999999\n\
");
wmm_lines = malloc(sizeof(char*) * 256);
if (!wmm_lines) {
fprintf(stderr, "malloc fail in geomag.c\n");
return -1;
}
wmm_index = 0;
char *saveptr = NULL;
wmm_lines[wmm_index] = strtok_r(wmm_string, "\n", &saveptr);
while (wmm_lines[wmm_index]) {
wmm_index++;
wmm_lines[wmm_index] = strtok_r(NULL, "\n", &saveptr);
}
if (wmm_lines[0] == NULL || sscanf(wmm_lines[0],"%lf%s",&epochlowlim,modl) < 2)
{
fprintf(stderr, "Invalid header in model wmm_string in geomag.c\n");
return -1;
}
/* INITIALIZE GEOMAG ROUTINE */
maxdeg = 12;
int result = geomag_E0_init(&maxdeg);
free(wmm_lines);
wmm_lines = NULL;
free(wmm_string);
wmm_string = NULL;
return result;
}
/*************************************************************************/
static int E0000(int IENTRY, int *maxdeg, double alt, double glat, double glon, double time, double *dec, double *dip, double *ti, double *gv)
{
static int maxord,i,icomp,n,m,j,D1,D2,D3,D4;
static double c[13][13],cd[13][13],tc[13][13],dp[13][13],snorm[169],
sp[13],cp[13],fn[13],fm[13],pp[13],k[13][13],pi,dtr,a,b,re,
a2,b2,c2,a4,b4,c4,gnm,hnm,dgnm,dhnm,flnmj,
dt,rlon,rlat,srlon,srlat,crlon,crlat,srlat2,
crlat2,q,q1,q2,ct,st,r2,r,d,ca,sa,aor,ar,br,bt,bp,bpp,
par,temp1,temp2,parp,bx,by,bz,bh;
static char model[20], c_new[5];
static double *p = snorm;
switch(IENTRY){case 0: goto INIT; case 1: goto CALC;}
INIT:
/* INITIALIZE CONSTANTS */
maxord = *maxdeg;
sp[0] = 0.0;
cp[0] = *p = pp[0] = 1.0;
dp[0][0] = 0.0;
a = 6378.137;
b = 6356.7523142;
re = 6371.2;
a2 = a*a;
b2 = b*b;
c2 = a2-b2;
a4 = a2*a2;
b4 = b2*b2;
c4 = a4 - b4;
/* READ WORLD MAGNETIC MODEL SPHERICAL HARMONIC COEFFICIENTS */
c[0][0] = 0.0;
cd[0][0] = 0.0;
wmm_index = 0;
if (wmm_lines[wmm_index] == NULL || sscanf(wmm_lines[wmm_index],"%lf%s",&epoch,model) < 2)
{
fprintf(stderr, "Invalid header in model wmm_string in geomag.c\n");
return -1;
}
S3:
wmm_index++;
if (wmm_lines[wmm_index] == NULL) goto S4;
/* CHECK FOR LAST LINE IN FILE */
for (i=0; i<4 && (wmm_lines[wmm_index][i] != '\0'); i++)
{
c_new[i] = wmm_lines[wmm_index][i];
c_new[i+1] = '\0';
}
icomp = strcmp("9999", c_new);
if (icomp == 0) goto S4;
/* END OF FILE NOT ENCOUNTERED, GET VALUES */
sscanf(wmm_lines[wmm_index], "%d%d%lf%lf%lf%lf",&n,&m,&gnm,&hnm,&dgnm,&dhnm);
if (n > maxord) goto S4;
if (m > n || m < 0.0)
{
fprintf(stderr, "%d\n", wmm_index);
fprintf(stderr, "Corrupt record in model wmm_string in geomag.c\n");
return -1;
}
if (m <= n)
{
c[m][n] = gnm;
cd[m][n] = dgnm;
if (m != 0)
{
c[n][m-1] = hnm;
cd[n][m-1] = dhnm;
}
}
goto S3;
/* CONVERT SCHMIDT NORMALIZED GAUSS COEFFICIENTS TO UNNORMALIZED */
S4:
*snorm = 1.0;
fm[0] = 0.0;
for (n=1; n<=maxord; n++)
{
*(snorm+n) = *(snorm+n-1)*(double)(2*n-1)/(double)n;
j = 2;
for (m=0,D1=1,D2=(n-m+D1)/D1; D2>0; D2--,m+=D1)
{
k[m][n] = (double)(((n-1)*(n-1))-(m*m))/(double)((2*n-1)*(2*n-3));
if (m > 0)
{
flnmj = (double)((n-m+1)*j)/(double)(n+m);
*(snorm+n+m*13) = *(snorm+n+(m-1)*13)*sqrt(flnmj);
j = 1;
c[n][m-1] = *(snorm+n+m*13)*c[n][m-1];
cd[n][m-1] = *(snorm+n+m*13)*cd[n][m-1];
}
c[m][n] = *(snorm+n+m*13)*c[m][n];
cd[m][n] = *(snorm+n+m*13)*cd[m][n];
}
fn[n] = (double)(n+1);
fm[n] = (double)n;
}
k[1][1] = 0.0;
return 0;
/*************************************************************************/
CALC:
dt = time - epoch;
pi = 3.14159265359;
dtr = pi/180.0;
rlon = glon*dtr;
rlat = glat*dtr;
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,D3=1,D4=(n+m+D3)/D3; D4>0; D4--,m+=D3)
{
/*
COMPUTE UNNORMALIZED ASSOCIATED LEGENDRE POLYNOMIALS
AND DERIVATIVES VIA RECURSION RELATIONS
*/
if (n == m)
{
*(p+n+m*13) = st**(p+n-1+(m-1)*13);
dp[m][n] = st*dp[m-1][n-1]+ct**(p+n-1+(m-1)*13);
goto S50;
}
if (n == 1 && m == 0)
{
*(p+n+m*13) = ct**(p+n-1+m*13);
dp[m][n] = ct*dp[m][n-1]-st**(p+n-1+m*13);
goto S50;
}
if (n > 1 && n != m)
{
if (m > n-2) *(p+n-2+m*13) = 0.0;
if (m > n-2) dp[m][n-2] = 0.0;
*(p+n+m*13) = ct**(p+n-1+m*13)-k[m][n]**(p+n-2+m*13);
dp[m][n] = ct*dp[m][n-1] - st**(p+n-1+m*13)-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+n+m*13);
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)/dtr;
*dip = atan2(bz,bh)/dtr;
/*
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 > +180.0) *gv -= 360.0;
if (*gv < -180.0) *gv += 360.0;
}
return 0;
}
/*************************************************************************/
static int geomag_E0_init(int *maxdeg)
{
return E0000(0,maxdeg,0.0,0.0,0.0,0.0,NULL,NULL,NULL,NULL);
}
/*************************************************************************/
int geomag_calc(double alt, double glat, double glon, double time, double *dec, double *dip, double *ti, double *gv)
{
return E0000(1,NULL,alt,glat,glon,time,dec,dip,ti,gv);
}
/*************************************************************************/
static char geomag_introduction(double epochlowlim)
{
char help;
static char ans;
int res = 0;
res++;
printf("\n\n Welcome to the World Magnetic Model (WMM) %4.0lf C-Program\n\n", epochlowlim);
printf(" --- Version 3.0, January 2010 ---\n\n");
printf("\n This program estimates the strength and direction of ");
printf("\n Earth's main magnetic field for a given point/area.");
printf("\n Enter h for help and contact information or c to continue.");
printf ("\n >");
res = scanf("%c%*[^\n]",&help);
getchar();
if ((help == 'h') || (help == 'H'))
{
printf("\n Help information ");
printf("\n The World Magnetic Model (WMM) for %7.2lf", epochlowlim);
printf("\n is a model of Earth's main magnetic field. The WMM");
printf("\n is recomputed every five (5) years, in years divisible by ");
printf("\n five (i.e. 2010, 2015). See the contact information below");
printf("\n to obtain more information on the WMM and associated software.");
printf("\n ");
printf("\n Input required is the location in geodetic latitude and");
printf("\n longitude (positive for northern latitudes and eastern ");
printf("\n longitudes), geodetic altitude in meters, and the date of ");
printf("\n interest in years.");
printf("\n\n\n The program computes the estimated magnetic Declination");
printf("\n (D) which is sometimes called MAGVAR, Inclination (I), Total");
printf("\n Intensity (F or TI), Horizontal Intensity (H or HI), Vertical");
printf("\n Intensity (Z), and Grid Variation (GV). Declination and Grid");
printf("\n Variation are measured in units of degrees and are considered");
printf("\n positive when east or north. Inclination is measured in units");
printf("\n of degrees and is considered positive when pointing down (into");
printf("\n the Earth). The WMM is reference to the WGS-84 ellipsoid and");
printf("\n is valid for 5 years after the base epoch.");
printf("\n\n\n It is very important to note that a degree and order 12 model,");
printf("\n such as WMM, describes only the long wavelength spatial magnetic ");
printf("\n fluctuations due to Earth's core. Not included in the WMM series");
printf("\n models are intermediate and short wavelength spatial fluctuations ");
printf("\n that originate in Earth's mantle and crust. Consequently, isolated");
printf("\n angular errors at various positions on the surface (primarily over");
printf("\n land, incontinental margins and over oceanic seamounts, ridges and");
printf("\n trenches) of several degrees may be expected. Also not included in");
printf("\n the model are temporal fluctuations of magnetospheric and ionospheric");
printf("\n origin. On the days during and immediately following magnetic storms,");
printf("\n temporal fluctuations can cause substantial deviations of the geomagnetic");
printf("\n field from model values. If the required declination accuracy is");
printf("\n more stringent than the WMM series of models provide, the user is");
printf("\n advised to request special (regional or local) surveys be performed");
printf("\n and models prepared. Please make requests of this nature to the");
printf("\n National Geospatial-Intelligence Agency (NGA) at the address below.");
printf("\n\n\n Contact Information");
printf("\n Software and Model Support");
printf("\n National Geophysical Data Center");
printf("\n NOAA EGC/2");
printf("\n 325 Broadway");
printf("\n Boulder, CO 80303 USA");
printf("\n Attn: Susan McLean or Stefan Maus");
printf("\n Phone: (303) 497-6478 or -6522");
printf("\n Email: [email protected] or [email protected] ");
printf("\n\n\n Continue with program? (y or n) ");
res = scanf("%c%*[^\n]", &ans);
getchar();
}
else
{
ans = 'y';
}
return(ans);
}
void geomag_interactive() {
int warn_H, warn_H_strong, warn_P;
double warn_H_val, warn_H_strong_val;
char answer;
double x1,x2,y1,y2,z1,z2,h1,h2;
double altm, dlat, dlon;
double ati, adec, adip;
double alt, time, dec, dip, ti, gv;
double time1, dec1, dip1, ti1;
double dec2, dip2, ti2;
double ax,ay,az,ah;
double rTd=0.017453292;
double epochrange = 5.0;
double dmin, imin, ddeg, ideg;
int res = 0;
res++;
char ans = geomag_introduction(epochlowlim);
if ((ans == 'y') || (ans == 'Y'))
S1:
maxdeg = 12;
warn_H = 0;
warn_H_val = 99999.0;
warn_H_strong = 0;
warn_H_strong_val = 99999.0;
warn_P = 0;
printf("\n\n\nENTER LATITUDE IN DECIMAL DEGREES ");
printf("\n(North latitude positive, South latitude negative \n");
printf("i.e. 25.5 for 25 degrees 30 minutes north.) \n");
res = scanf("%lf%*[^\n]", &dlat);
getchar();
printf("ENTER LONGITUDE IN DECIMAL DEGREES");
printf("(East longitude positive, West negative \n");
printf("i.e.- 100.0 for 100.0 degrees west.)\n");
res = scanf("%lf%*[^\n]", &dlon);
getchar();
printf("ENTER ALTITUDE IN KILOMETERS ABOVE WGS84 ELLIPSOID\n");
res = scanf("%lf%*[^\n]", &altm);
getchar();
alt = altm;
epochuplim = epochlowlim + epochrange;
printf("ENTER TIME IN DECIMAL YEAR (%-7.2lf - %-7.2lf)\n",epochlowlim,epochuplim);
res = scanf("%lf%*[^\n]",&time);
getchar();
double dt = time - epoch;
printf("%.1f %.1f\n", time, epoch);
if (time < 0.0 || (dt < 0.0 || dt > 5.0))
{
printf("\n\n WARNING - TIME EXTENDS BEYOND MODEL 5-YEAR LIFE SPAN");
printf("\n CONTACT NGDC FOR PRODUCT UPDATES:");
printf("\n National Geophysical Data Center");
printf("\n NOAA EGC/2");
printf("\n 325 Broadway");
printf("\n Boulder, CO 80303 USA");
printf("\n Attn: Manoj Nair or Stefan Maus");
printf("\n Phone: (303) 497-4642 or -6522");
printf("\n Email: [email protected]");
printf("\n or");
printf("\n [email protected]");
printf("\n Web: http://www.ngdc.noaa.gov/geomag/WMM/");
printf("\n\n EPOCH = %.3lf",epoch);
printf("\n TIME = %.3lf",time);
printf("\n Do you wish to continue? (y or n) ");
res = scanf("%c%*[^\n]",&answer);
getchar();
if ((answer == 'n') || (answer == 'N'))
goto MORE;
}
geomag_calc(alt,dlat,dlon,time,&dec,&dip,&ti,&gv);
time1 = time;
dec1 = dec;
dip1 = dip;
ti1 = ti;
time = time1 + 1.0;
geomag_calc(alt,dlat,dlon,time,&dec,&dip,&ti,&gv);
dec2 = dec;
dip2 = dip;
ti2 = ti;
/*COMPUTE X, Y, Z, AND H COMPONENTS OF THE MAGNETIC FIELD*/
x1=ti1*(cos((dec1*rTd))*cos((dip1*rTd)));
x2=ti2*(cos((dec2*rTd))*cos((dip2*rTd)));
y1=ti1*(cos((dip1*rTd))*sin((dec1*rTd)));
y2=ti2*(cos((dip2*rTd))*sin((dec2*rTd)));
z1=ti1*(sin((dip1*rTd)));
z2=ti2*(sin((dip2*rTd)));
h1=ti1*(cos((dip1*rTd)));
h2=ti2*(cos((dip2*rTd)));
/* COMPUTE ANNUAL CHANGE FOR TOTAL INTENSITY */
ati = ti2 - ti1;
/* COMPUTE ANNUAL CHANGE FOR DIP & DEC */
adip = (dip2 - dip1) * 60.;
adec = (dec2 - dec1) * 60.;
/* COMPUTE ANNUAL CHANGE FOR X, Y, Z, AND H */
ax = x2-x1;
ay = y2-y1;
az = z2-z1;
ah = h2-h1;
if (dec1 < 0.0) {
strcpy (decd,"(WEST)");
}
else
{
strcpy(decd,"(EAST)");
}
if (dip1 < 0.0)
{
strcpy(dipd,"(UP) ");
}
else
{
strcpy(dipd,"(DOWN)");
}
/* deal with geographic and magnetic poles */
if (h1 < 100.0) /* at magnetic poles */
{
dec1 = NaN;
adec = NaN;
strcpy(decd,"(VOID)");
/* while rest is ok */
}
if (h1 < 1000.0)
{
warn_H = 0;
warn_H_strong = 1;
warn_H_strong_val = h1;
}
else if (h1 < 5000.0 && !warn_H_strong)
{
warn_H = 1;
warn_H_val = h1;
}
/* convert D and I to deg and min */
if (my_isnan(dec1)) ddeg = dec1; else ddeg=(int)dec1;
dmin=(dec1-(double)ddeg)*60;
if (dec1 > 0 && dmin >= 59.5)
{
dmin -= 60.0;
ddeg++;
}
if (dec1 < 0 && dmin <= -59.5)
{
dmin += 60.0;
ddeg--;
}
if(ddeg!=0) dmin=fabs(dmin);
if (my_isnan(dip1)) ideg = dip1; else ideg=(int)dip1;
imin=(dip1-(double)ideg)*60;
if (dip1 > 0 && imin >= 59.5)
{
imin -= 60.0;
ideg++;
}
if (dip1 < 0 && imin <= -59.5)
{
imin += 60.0;
ideg--;
}
if(ideg!=0) imin=fabs(imin);
printf("\n Results For \n");
if (dlat < 0)
printf("\n LATITUDE: %7.2lfS",-dlat);
else
printf("\n LATITUDE: %7.2lfN",dlat);
if (dlon < 0)
printf("\n LONGITUDE: %7.2lfW",-dlon);
else
printf("\n LONGITUDE: %7.2lfE",dlon);
printf("\n ALTITUDE: %8.2lf KM ABOVE WGS84 ELLIPSOID",altm);
printf("\n DATE: %6.1lf\n",time1);
printf("\n Main Field \t\t\t Secular Change");
printf("\n F = %-9.1lf nT\t\t dF = %-8.1lf nT/yr",ti1,ati);
if (my_isnan(h1))
printf("\n H = NaN \t\t dH = NaN");
else
printf("\n H = %-9.1lf nT\t\t dH = %-8.1lf nT/yr",h1,ah);
if (my_isnan(x1))
printf("\n X = NaN \t\t dX = NaN");
else
printf("\n X = %-9.1lf nT\t\t dX = %-8.1lf nT/yr ",x1,ax);
if (my_isnan(y1))
printf("\n Y = NaN \t\t dY = NaN");
else
printf("\n Y = %-9.1lf nT\t\t dY = %-8.1lf nT/yr ",y1,ay);
printf("\n Z = %-9.1lf nT\t\t dZ = %-8.1lf nT/yr ",z1,az);
if (my_isnan(dec1))
printf("\n D = NaN \t\t dD = NaN");
else
printf("\n D = %4.0lf Deg %3.0lf Min %s\t dD = %-8.1lf Min/yr",ddeg,dmin,decd,adec);
printf("\n I = %4.0lf Deg %3.0lf Min %s\t dI = %-8.1lf Min/yr",ideg,imin,dipd,adip);
if (warn_H)
{
printf("\n\nWarning: The horizontal field strength at this location is only %6.1lf nT\n",warn_H_val);
printf(" Compass readings have large uncertainties in areas where H is\n");
printf(" smaller than 5000 nT\n");
}
if (warn_H_strong)
{
printf("\n\nWarning: The horizontal field strength at this location is only %6.1lf nT\n",warn_H_strong_val);
printf(" Compass readings have VERY LARGE uncertainties in areas where H is\n");
printf(" smaller than 1000 nT\n");
}
if (warn_P)
{
printf("\n\nWarning: Location is at geographic pole where X, Y, and Decl are undefined\n");
}
MORE:
printf("\n\nDO YOU NEED MORE POINT DATA? (y or n) ");
res = scanf("%c%*[^\n]", &answer);
getchar();
if ((answer =='y')||(answer == 'Y')) goto S1;
else
{
printf("%s",goodbye);
}
}