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geomag70.c
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/* http://lists.openstreetmap.org/pipermail/talk/2008-September/029424.html */
/****************************************************************************/
/* */
/* NGDC's Geomagnetic Field Modeling software for the IGRF and WMM */
/* */
/****************************************************************************/
/* */
/* Disclaimer: This program has undergone limited testing. It is */
/* being distributed unoffically. The National Geophysical Data */
/* Center does not guarantee it's correctness. */
/* */
/****************************************************************************/
/* */
/* Version 7.0: */
/* - input file format changed to */
/* -- accept new DGRF2005 coeffs with 0.01 nT precision */
/* -- make sure all values are separated by blanks */
/* -- swapped n and m: first is degree, second is order */
/* - new my_isnan function improves portablility */
/* - corrected feet to km conversion factor */
/* - fixed date conversion errors for yyyy,mm,dd format */
/* - fixed lon/lat conversion errors for deg,min,sec format */
/* - simplified leap year identification */
/* - changed comment: units of ddot and idot are arc-min/yr */
/* - added note that this program computes the secular variation as */
/* the 1-year difference, rather than the instantaneous change, */
/* which can be slightly different */
/* - clarified that height is above ellipsoid, not above mean sea level */
/* although the difference is negligible for magnetics */
/* - changed main(argv,argc) to usual definition main(argc,argv) */
/* - corrected rounding of angles close to 60 minutes */
/* Thanks to all who provided bug reports and suggested fixes */
/* */
/* Stefan Maus Jan-25-2010 */
/* */
/****************************************************************************/
/* */
/* Version 6.1: */
/* Included option to read coordinates from a file and output the */
/* results to a new file, repeating the input and adding columns */
/* for the output */
/* Stefan Maus Jan-31-2008 */
/* */
/****************************************************************************/
/* */
/* Version 6.0: */
/* Bug fixes for the interpolation between models. Also added warnings */
/* for declination at low H and corrected behaviour at geogr. poles. */
/* Placed print-out commands into separate routines to facilitate */
/* fine-tuning of the tables */
/* Stefan Maus Aug-24-2004 */
/* */
/****************************************************************************/
#include <all.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>
#include <geomag70.h>
#define NaN log(-1.0)
#define FT2KM (1.0/0.0003048)
#define RAD2DEG (180.0/PI)
#define IEXT 0
#define FALSE 0
#define TRUE 1 /* constants */
#define RECL 81
#define MAXINBUFF RECL+14
#define MAXREAD MAXINBUFF-2
#define MAXMOD 30
#define PATH MAXREAD
#define EXT_COEFF1 (double)0
#define EXT_COEFF2 (double)0
#define EXT_COEFF3 (double)0
#define MAXDEG 13
#define MAXCOEFF (MAXDEG*(MAXDEG+2)+1) /* index starts with 1!, (from old Fortran?) */
static void print_result(double date, double d, double i, double h, double x, double y, double z, double f, int *ret_dd, int *ret_dm, int *ret_id, int *ret_im);
static double julday();
static int interpsh();
static int extrapsh();
static int shval3();
static int dihf();
static int getshc();
static double gh1[MAXCOEFF];
static double gh2[MAXCOEFF];
static double gha[MAXCOEFF]; /* Geomag global variables */
static double ghb[MAXCOEFF];
static double d = 0, f = 0, h = 0, i = 0;
static double dtemp, ftemp, htemp, itemp;
static double x = 0, y = 0, z = 0;
static double xtemp, ytemp, ztemp;
static int nmax;
static double sdate = -1;
/****************************************************************************/
/* */
/* Program Geomag */
/* */
/****************************************************************************/
/* */
/* This program, originally written in FORTRAN, was developed using */
/* subroutines written by */
/* A. Zunde */
/* USGS, MS 964, Box 25046 Federal Center, Denver, Co. 80225 */
/* and */
/* S.R.C. Malin & D.R. Barraclough */
/* Institute of Geological Sciences, United Kingdom. */
/* */
/* Translated */
/* into C by : Craig H. Shaffer */
/* 29 July, 1988 */
/* */
/* Rewritten by : David Owens */
/* For Susan McLean */
/* */
/* Maintained by: Stefan Maus */
/* Contact : [email protected] */
/* National Geophysical Data Center */
/* World Data Center-A for Solid Earth Geophysics */
/* NOAA, E/GC1, 325 Broadway, */
/* Boulder, CO 80303 */
/* */
/* */
/****************************************************************************/
int init_declination(char *mdfile, int year, int month, int day) {
int modelI;
int max1[MAXMOD];
int max2[MAXMOD];
int max3[MAXMOD];
int fileline;
long irec_pos[MAXMOD];
char inbuff[MAXINBUFF];
char model[MAXMOD][9];
double epoch[MAXMOD];
double yrmin[MAXMOD];
double yrmax[MAXMOD];
double minyr = 0;
double maxyr = 0;
double altmin[MAXMOD];
double altmax[MAXMOD];
FILE *stream = NULL; /* Pointer to specified model data file */
inbuff[MAXREAD + 1] = '\0'; /* Just to protect mem. */
inbuff[MAXINBUFF - 1] = '\0'; /* Just to protect mem. */
stream = fopen(mdfile, "rt");
if (stream == NULL) {
SDL_Log("geomag: file not found: %s\n", mdfile);
return 0;
}
fileline = 0; /* First line will be 1 */
modelI = -1; /* First model will be 0 */
while (fgets(inbuff, MAXREAD, stream)) {
fileline++; /* On new line */
// if (strlen(inbuff) != RECL + 1) {
// SDL_Log("Corrupt record in file %s on line %d.\n", mdfile, fileline);
// fclose(stream);
// exit(5);
// }
if (!strncmp(inbuff, " ", 3)) {
modelI++; /* New model */
if (modelI > MAXMOD) {
SDL_Log("Too many models in file %s on line %d.", mdfile, fileline);
fclose(stream);
return 6;
}
irec_pos[modelI] = ftell(stream);
sscanf(inbuff, "%s%lg%d%d%d%lg%lg%lg%lg", model[modelI], &epoch[modelI], &max1[modelI], &max2[modelI], &max3[modelI], &yrmin[modelI], &yrmax[modelI], &altmin[modelI], &altmax[modelI]);
if (modelI == 0) {
minyr = yrmin[0];
maxyr = yrmax[0];
} else {
if (yrmin[modelI] < minyr) {
minyr = yrmin[modelI];
}
if (yrmax[modelI] > maxyr) {
maxyr = yrmax[modelI];
}
}
}
}
fclose(stream);
sdate = julday(month, day, year);
if ((sdate > maxyr) && (sdate < maxyr + 1)) {
SDL_Log("\nWarning: The date %4.2f is out of range,\n", sdate);
SDL_Log(" but still within one year of model expiration date.\n");
SDL_Log(" An updated model file is available before 1.1.%4.0f\n", maxyr);
}
if (max2[modelI] == 0) {
getshc(mdfile, 1, irec_pos[modelI], max1[modelI], 1);
getshc(mdfile, 1, irec_pos[modelI + 1], max1[modelI + 1], 2);
nmax = interpsh(sdate, yrmin[modelI], max1[modelI], yrmin[modelI + 1], max1[modelI + 1], 3);
nmax = interpsh(sdate + 1, yrmin[modelI] , max1[modelI], yrmin[modelI + 1], max1[modelI + 1], 4);
} else {
getshc(mdfile, 1, irec_pos[modelI], max1[modelI], 1);
getshc(mdfile, 0, irec_pos[modelI], max2[modelI], 2);
nmax = extrapsh(sdate, epoch[modelI], max1[modelI], max2[modelI], 3);
nmax = extrapsh(sdate + 1, epoch[modelI], max1[modelI], max2[modelI], 4);
}
return 0;
}
int get_declination(double latitude, double longitude, double alt, int *ret_dd, int *ret_dm, int *ret_id, int *ret_im) {
alt *= 0.001;
shval3(1, latitude, longitude, alt, nmax, 3, IEXT, EXT_COEFF1, EXT_COEFF2, EXT_COEFF3);
dihf(3);
shval3(1, latitude, longitude, alt, nmax, 4, IEXT, EXT_COEFF1, EXT_COEFF2, EXT_COEFF3);
dihf(4);
d = d * (RAD2DEG);
i = i * (RAD2DEG);
if (h < 100.0) {
d = NaN;
}
if (90.0 - fabs(latitude) <= 0.001) {
x = NaN;
y = NaN;
d = NaN;
}
print_result(sdate, d, i, h, x, y, z, f, ret_dd, ret_dm, ret_id, ret_im);
return 0;
}
static void print_result(double date, double d, double i, double h, double x, double y, double z, double f, int *ret_dd, int *ret_dm, int *ret_id, int *ret_im) {
int ddeg, ideg;
double dmin, imin;
/* Change d and i to deg and min */
ddeg = (int)d;
dmin = (d - (double)ddeg) * 60;
if (d > 0 && dmin >= 59.5) {
dmin -= 60.0;
ddeg++;
}
if (d < 0 && dmin <= -59.5) {
dmin += 60.0;
ddeg--;
}
if (ddeg != 0) {
dmin = fabs(dmin);
}
ideg = (int)i;
imin = (i - (double)ideg) * 60;
if (i > 0 && imin >= 59.5) {
imin -= 60.0;
ideg++;
}
if (i < 0 && imin <= -59.5) {
imin += 60.0;
ideg--;
}
if (ideg != 0) {
imin = fabs(imin);
}
*ret_dd = (int)ddeg;
*ret_dm = (int)dmin;
*ret_id = (int)ideg;
*ret_im = (int)imin;
// SDL_Log("%id %im\n", ddeg, (int)dmin);
return;
} /* print_result */
/****************************************************************************/
/* */
/* Subroutine julday */
/* */
/****************************************************************************/
/* */
/* Computes the decimal day of year from month, day, year. */
/* Supplied by Daniel Bergstrom */
/* */
/* References: */
/* */
/* 1. Nachum Dershowitz and Edward M. Reingold, Calendrical Calculations, */
/* Cambridge University Press, 3rd edition, ISBN 978-0-521-88540-9. */
/* */
/* 2. Claus Tøndering, Frequently Asked Questions about Calendars, */
/* Version 2.9, http://www.tondering.dk/claus/calendar.html */
/* */
/****************************************************************************/
static double julday(month, day, year)
int month;
int day;
int year;
{
int days[12] = { 0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334};
int leap_year = (((year % 4) == 0) &&
(((year % 100) != 0) || ((year % 400) == 0)));
double day_in_year = (days[month - 1] + day + (month > 2 ? leap_year : 0));
return ((double)year + (day_in_year / (365.0 + leap_year)));
}
/****************************************************************************/
/* */
/* Subroutine getshc */
/* */
/****************************************************************************/
/* */
/* Reads spherical harmonic coefficients from the specified */
/* model into an array. */
/* */
/* Input: */
/* stream - Logical unit number */
/* iflag - Flag for SV equal to ) or not equal to 0 */
/* for designated read statements */
/* strec - Starting record number to read from model */
/* nmax_of_gh - Maximum degree and order of model */
/* */
/* Output: */
/* gh1 or 2 - Schmidt quasi-normal internal spherical */
/* harmonic coefficients */
/* */
/* FORTRAN */
/* Bill Flanagan */
/* NOAA CORPS, DESDIS, NGDC, 325 Broadway, Boulder CO. 80301 */
/* */
/* C */
/* C. H. Shaffer */
/* Lockheed Missiles and Space Company, Sunnyvale CA */
/* August 15, 1988 */
/* */
/****************************************************************************/
static int getshc(file, iflag, strec, nmax_of_gh, gh)
char file[PATH];
int iflag;
long int strec;
int nmax_of_gh;
int gh;
{
char inbuff[MAXINBUFF];
char irat[9];
int ii, m, n, mm, nn;
int ios = 0;
int line_num = 0;
double g, hh;
double trash;
FILE *stream = NULL; /* Pointer to specified model data file */
stream = fopen(file, "rt");
if (stream == NULL) {
SDL_Log("\nError on opening file %s", file);
} else {
ii = 0;
ios = 0;
fseek(stream, strec, 0);
for (nn = 1; nn <= nmax_of_gh; ++nn) {
for (mm = 0; mm <= nn; ++mm) {
if (iflag == 1) {
fgets(inbuff, MAXREAD, stream);
sscanf(inbuff, "%d%d%lg%lg%lg%lg%s%d",
&n, &m, &g, &hh, &trash, &trash, irat, &line_num);
} else {
fgets(inbuff, MAXREAD, stream);
sscanf(inbuff, "%d%d%lg%lg%lg%lg%s%d",
&n, &m, &trash, &trash, &g, &hh, irat, &line_num);
}
if ((nn != n) || (mm != m)) {
ios = -2;
fclose(stream);
return (ios);
}
ii = ii + 1;
switch (gh) {
case 1:
gh1[ii] = g;
break;
case 2:
gh2[ii] = g;
break;
default:
SDL_Log("\nError in subroutine getshc");
break;
}
if (m != 0) {
ii = ii + 1;
switch (gh) {
case 1:
gh1[ii] = hh;
break;
case 2:
gh2[ii] = hh;
break;
default:
SDL_Log("\nError in subroutine getshc");
break;
}
}
}
}
}
fclose(stream);
return (ios);
}
/****************************************************************************/
/* */
/* Subroutine extrapsh */
/* */
/****************************************************************************/
/* */
/* Extrapolates linearly a spherical harmonic model with a */
/* rate-of-change model. */
/* */
/* Input: */
/* date - date of resulting model (in decimal year) */
/* dte1 - date of base model */
/* nmax1 - maximum degree and order of base model */
/* gh1 - Schmidt quasi-normal internal spherical */
/* harmonic coefficients of base model */
/* nmax2 - maximum degree and order of rate-of-change model */
/* gh2 - Schmidt quasi-normal internal spherical */
/* harmonic coefficients of rate-of-change model */
/* */
/* Output: */
/* gha or b - Schmidt quasi-normal internal spherical */
/* harmonic coefficients */
/* nmax - maximum degree and order of resulting model */
/* */
/* FORTRAN */
/* A. Zunde */
/* USGS, MS 964, box 25046 Federal Center, Denver, CO. 80225 */
/* */
/* C */
/* C. H. Shaffer */
/* Lockheed Missiles and Space Company, Sunnyvale CA */
/* August 16, 1988 */
/* */
/****************************************************************************/
static int extrapsh(date, dte1, nmax1, nmax2, gh)
double date;
double dte1;
int nmax1;
int nmax2;
int gh;
{
int nmax;
int k, l;
int ii;
double factor;
factor = date - dte1;
if (nmax1 == nmax2) {
k = nmax1 * (nmax1 + 2);
nmax = nmax1;
} else {
if (nmax1 > nmax2) {
k = nmax2 * (nmax2 + 2);
l = nmax1 * (nmax1 + 2);
switch (gh) {
case 3:
for (ii = k + 1; ii <= l; ++ii) {
gha[ii] = gh1[ii];
}
break;
case 4:
for (ii = k + 1; ii <= l; ++ii) {
ghb[ii] = gh1[ii];
}
break;
default:
SDL_Log("\nError in subroutine extrapsh");
break;
}
nmax = nmax1;
} else {
k = nmax1 * (nmax1 + 2);
l = nmax2 * (nmax2 + 2);
switch (gh) {
case 3:
for (ii = k + 1; ii <= l; ++ii) {
gha[ii] = factor * gh2[ii];
}
break;
case 4:
for (ii = k + 1; ii <= l; ++ii) {
ghb[ii] = factor * gh2[ii];
}
break;
default:
SDL_Log("\nError in subroutine extrapsh");
break;
}
nmax = nmax2;
}
}
switch (gh) {
case 3:
for (ii = 1; ii <= k; ++ii) {
gha[ii] = gh1[ii] + factor * gh2[ii];
}
break;
case 4:
for (ii = 1; ii <= k; ++ii) {
ghb[ii] = gh1[ii] + factor * gh2[ii];
}
break;
default:
SDL_Log("\nError in subroutine extrapsh");
break;
}
return (nmax);
}
/****************************************************************************/
/* */
/* Subroutine interpsh */
/* */
/****************************************************************************/
/* */
/* Interpolates linearly, in time, between two spherical harmonic */
/* models. */
/* */
/* Input: */
/* date - date of resulting model (in decimal year) */
/* dte1 - date of earlier model */
/* nmax1 - maximum degree and order of earlier model */
/* gh1 - Schmidt quasi-normal internal spherical */
/* harmonic coefficients of earlier model */
/* dte2 - date of later model */
/* nmax2 - maximum degree and order of later model */
/* gh2 - Schmidt quasi-normal internal spherical */
/* harmonic coefficients of internal model */
/* */
/* Output: */
/* gha or b - coefficients of resulting model */
/* nmax - maximum degree and order of resulting model */
/* */
/* FORTRAN */
/* A. Zunde */
/* USGS, MS 964, box 25046 Federal Center, Denver, CO. 80225 */
/* */
/* C */
/* C. H. Shaffer */
/* Lockheed Missiles and Space Company, Sunnyvale CA */
/* August 17, 1988 */
/* */
/****************************************************************************/
static int interpsh(date, dte1, nmax1, dte2, nmax2, gh)
double date;
double dte1;
int nmax1;
double dte2;
int nmax2;
int gh;
{
int nmax;
int k, l;
int ii;
double factor;
factor = (date - dte1) / (dte2 - dte1);
if (nmax1 == nmax2) {
k = nmax1 * (nmax1 + 2);
nmax = nmax1;
} else {
if (nmax1 > nmax2) {
k = nmax2 * (nmax2 + 2);
l = nmax1 * (nmax1 + 2);
switch (gh) {
case 3:
for (ii = k + 1; ii <= l; ++ii) {
gha[ii] = gh1[ii] + factor * (-gh1[ii]);
}
break;
case 4:
for (ii = k + 1; ii <= l; ++ii) {
ghb[ii] = gh1[ii] + factor * (-gh1[ii]);
}
break;
default:
SDL_Log("\nError in subroutine extrapsh");
break;
}
nmax = nmax1;
} else {
k = nmax1 * (nmax1 + 2);
l = nmax2 * (nmax2 + 2);
switch (gh) {
case 3:
for (ii = k + 1; ii <= l; ++ii) {
gha[ii] = factor * gh2[ii];
}
break;
case 4:
for (ii = k + 1; ii <= l; ++ii) {
ghb[ii] = factor * gh2[ii];
}
break;
default:
SDL_Log("\nError in subroutine extrapsh");
break;
}
nmax = nmax2;
}
}
switch (gh) {
case 3:
for (ii = 1; ii <= k; ++ii) {
gha[ii] = gh1[ii] + factor * (gh2[ii] - gh1[ii]);
}
break;
case 4:
for (ii = 1; ii <= k; ++ii) {
ghb[ii] = gh1[ii] + factor * (gh2[ii] - gh1[ii]);
}
break;
default:
SDL_Log("\nError in subroutine extrapsh");
break;
}
return (nmax);
}
/****************************************************************************/
/* */
/* Subroutine shval3 */
/* */
/****************************************************************************/
/* */
/* Calculates field components from spherical harmonic (sh) */
/* models. */
/* */
/* Input: */
/* igdgc - indicates coordinate system used; set equal */
/* to 1 if geodetic, 2 if geocentric */
/* latitude - north latitude, in degrees */
/* longitude - east longitude, in degrees */
/* elev - WGS84 altitude above ellipsoid (igdgc=1), or */
/* radial distance from earth's center (igdgc=2) */
/* a2,b2 - squares of semi-major and semi-minor axes of */
/* the reference spheroid used for transforming */
/* between geodetic and geocentric coordinates */
/* or components */
/* nmax - maximum degree and order of coefficients */
/* iext - external coefficients flag (=0 if none) */
/* ext1,2,3 - the three 1st-degree external coefficients */
/* (not used if iext = 0) */
/* */
/* Output: */
/* x - northward component */
/* y - eastward component */
/* z - vertically-downward component */
/* */
/* based on subroutine 'igrf' by D. R. Barraclough and S. R. C. Malin, */
/* report no. 71/1, institute of geological sciences, U.K. */
/* */
/* FORTRAN */
/* Norman W. Peddie */
/* USGS, MS 964, box 25046 Federal Center, Denver, CO. 80225 */
/* */
/* C */
/* C. H. Shaffer */
/* Lockheed Missiles and Space Company, Sunnyvale CA */
/* August 17, 1988 */
/* */
/****************************************************************************/
static int shval3(igdgc, flat, flon, elev, nmax, gh, iext, ext1, ext2, ext3)
int igdgc;
double flat;
double flon;
double elev;
int nmax;
int gh;
int iext;
double ext1;
double ext2;
double ext3;
{
double earths_radius = 6371.2;
double dtr = 0.01745329;
double slat;
double clat;
double ratio;
double aa, bb, cc, dd;
double sd;
double cd;
double r;
double a2;
double b2;
double rr = 0;
double fm = 0;
double fn = 0;
double sl[14];
double cl[14];
double p[119];
double q[119];
int ii, j, k, l, m, n;
int npq;
int ios;
double argument;
double power;
a2 = 40680631.59; /* WGS84 */
b2 = 40408299.98; /* WGS84 */
ios = 0;
r = elev;
argument = flat * dtr;
slat = sin(argument);
if ((90.0 - flat) < 0.001) {
aa = 89.999; /* 300 ft. from North pole */
} else {
if ((90.0 + flat) < 0.001) {
aa = -89.999;
} else {
aa = flat;
}
}
argument = aa * dtr;
clat = cos(argument);
argument = flon * dtr;
sl[1] = sin(argument);
cl[1] = cos(argument);
switch (gh) {
case 3:
x = 0;
y = 0;
z = 0;
break;
case 4:
xtemp = 0;
ytemp = 0;
ztemp = 0;
break;
default:
SDL_Log("\nError in subroutine shval3");
break;
}
sd = 0.0;
cd = 1.0;
l = 1;
n = 0;
m = 1;
npq = (nmax * (nmax + 3)) / 2;
if (igdgc == 1) {
aa = a2 * clat * clat;
bb = b2 * slat * slat;
cc = aa + bb;
argument = cc;
dd = sqrt(argument);
argument = elev * (elev + 2.0 * dd) + (a2 * aa + b2 * bb) / cc;
r = sqrt(argument);
cd = (elev + dd) / r;
sd = (a2 - b2) / dd * slat * clat / r;
aa = slat;
slat = slat * cd - clat * sd;
clat = clat * cd + aa * sd;
}
ratio = earths_radius / r;
argument = 3.0;
aa = sqrt(argument);
p[1] = 2.0 * slat;
p[2] = 2.0 * clat;
p[3] = 4.5 * slat * slat - 1.5;
p[4] = 3.0 * aa * clat * slat;
q[1] = -clat;
q[2] = slat;
q[3] = -3.0 * clat * slat;
q[4] = aa * (slat * slat - clat * clat);
for (k = 1; k <= npq; ++k) {
if (n < m) {
m = 0;
n = n + 1;
argument = ratio;
power = n + 2;
rr = pow(argument, power);
fn = n;
}
fm = m;
if (k >= 5) {
if (m == n) {
argument = (1.0 - 0.5 / fm);
aa = sqrt(argument);
j = k - n - 1;
p[k] = (1.0 + 1.0 / fm) * aa * clat * p[j];
q[k] = aa * (clat * q[j] + slat / fm * p[j]);
sl[m] = sl[m - 1] * cl[1] + cl[m - 1] * sl[1];
cl[m] = cl[m - 1] * cl[1] - sl[m - 1] * sl[1];
} else {
argument = fn * fn - fm * fm;
aa = sqrt(argument);
argument = ((fn - 1.0) * (fn - 1.0)) - (fm * fm);
bb = sqrt(argument) / aa;
cc = (2.0 * fn - 1.0) / aa;
ii = k - n;
j = k - 2 * n + 1;
p[k] = (fn + 1.0) * (cc * slat / fn * p[ii] - bb / (fn - 1.0) * p[j]);
q[k] = cc * (slat * q[ii] - clat / fn * p[ii]) - bb * q[j];
}
}
switch (gh) {
case 3:
aa = rr * gha[l];
break;
case 4:
aa = rr * ghb[l];
break;
default:
SDL_Log("\nError in subroutine shval3");
break;
}
if (m == 0) {
switch (gh) {
case 3:
x = x + aa * q[k];
z = z - aa * p[k];
break;
case 4:
xtemp = xtemp + aa * q[k];
ztemp = ztemp - aa * p[k];
break;
default:
SDL_Log("\nError in subroutine shval3");
break;
}
l = l + 1;
} else {
switch (gh) {
case 3:
bb = rr * gha[l + 1];
cc = aa * cl[m] + bb * sl[m];
x = x + cc * q[k];
z = z - cc * p[k];
if (clat > 0) {
y = y + (aa * sl[m] - bb * cl[m]) *
fm * p[k] / ((fn + 1.0) * clat);
} else {
y = y + (aa * sl[m] - bb * cl[m]) * q[k] * slat;
}
l = l + 2;
break;
case 4:
bb = rr * ghb[l + 1];
cc = aa * cl[m] + bb * sl[m];
xtemp = xtemp + cc * q[k];
ztemp = ztemp - cc * p[k];
if (clat > 0) {
ytemp = ytemp + (aa * sl[m] - bb * cl[m]) *
fm * p[k] / ((fn + 1.0) * clat);
} else {
ytemp = ytemp + (aa * sl[m] - bb * cl[m]) *
q[k] * slat;
}
l = l + 2;
break;
default:
SDL_Log("\nError in subroutine shval3");
break;
}
}
m = m + 1;
}
if (iext != 0) {
aa = ext2 * cl[1] + ext3 * sl[1];
switch (gh) {
case 3:
x = x - ext1 * clat + aa * slat;
y = y + ext2 * sl[1] - ext3 * cl[1];
z = z + ext1 * slat + aa * clat;
break;
case 4:
xtemp = xtemp - ext1 * clat + aa * slat;
ytemp = ytemp + ext2 * sl[1] - ext3 * cl[1];
ztemp = ztemp + ext1 * slat + aa * clat;
break;
default:
SDL_Log("\nError in subroutine shval3");
break;
}
}
switch (gh) {
case 3:
aa = x;
x = x * cd + z * sd;
z = z * cd - aa * sd;
break;
case 4:
aa = xtemp;
xtemp = xtemp * cd + ztemp * sd;
ztemp = ztemp * cd - aa * sd;
break;
default:
SDL_Log("\nError in subroutine shval3");
break;
}
return (ios);
}
/****************************************************************************/
/* */
/* Subroutine dihf */
/* */
/****************************************************************************/
/* */
/* Computes the geomagnetic d, i, h, and f from x, y, and z. */
/* */
/* Input: */
/* x - northward component */
/* y - eastward component */
/* z - vertically-downward component */
/* */
/* Output: */
/* d - declination */
/* i - inclination */
/* h - horizontal intensity */
/* f - total intensity */
/* */
/* FORTRAN */
/* A. Zunde */
/* USGS, MS 964, box 25046 Federal Center, Denver, CO. 80225 */
/* */
/* C */
/* C. H. Shaffer */
/* Lockheed Missiles and Space Company, Sunnyvale CA */
/* August 22, 1988 */
/* */
/****************************************************************************/
static int dihf(gh)
int gh;
{
int ios;
int j;
double sn;
double h2;
double hpx;
double argument, argument2;
ios = gh;
sn = 0.0001;
switch (gh) {
case 3:
for (j = 1; j <= 1; ++j) {
h2 = x * x + y * y;
argument = h2;
h = sqrt(argument); /* calculate horizontal intensity */
argument = h2 + z * z;
f = sqrt(argument); /* calculate total intensity */
if (f < sn) {
d = NaN; /* If d and i cannot be determined, */
i = NaN; /* set equal to NaN */
} else {
argument = z;
argument2 = h;
i = atan2(argument, argument2);
if (h < sn) {
d = NaN;
} else {
hpx = h + x;
if (hpx < sn) {
d = PI;
} else {
argument = y;
argument2 = hpx;
d = 2.0 * atan2(argument, argument2);
}
}
}
}
break;
case 4:
for (j = 1; j <= 1; ++j) {
h2 = xtemp * xtemp + ytemp * ytemp;
argument = h2;
htemp = sqrt(argument);
argument = h2 + ztemp * ztemp;
ftemp = sqrt(argument);
if (ftemp < sn) {
dtemp = NaN; /* If d and i cannot be determined, */
itemp = NaN; /* set equal to 999.0 */
} else {
argument = ztemp;
argument2 = htemp;
itemp = atan2(argument, argument2);
if (htemp < sn) {
dtemp = NaN;
} else {
hpx = htemp + xtemp;
if (hpx < sn) {
dtemp = PI;
} else {
argument = ytemp;