| 1 | /* DoD NIMA World Magnetic Model.
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| 2 | * from http://www.ngdc.noaa.gov
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| 3 | *
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| 4 | #define TEST_MAIN
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| 5 | */
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| 6 |
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| 7 |
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| 8 | #include <math.h>
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| 9 | #include <stdio.h>
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| 10 | #include <string.h>
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| 11 | #include <errno.h>
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| 12 |
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| 13 | #include "astro.h"
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| 14 |
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| 15 | static char mfn[] = "wmm.cof"; /* file with model coefficients */
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| 16 |
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| 17 | static int geomag(FILE *wmmdat, int *maxdeg);
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| 18 | static int geomg1(FILE *wmmdat, float alt, float glat, float glon,
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| 19 | float t, float *dec, float *mdp, float *ti, float *gv);
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| 20 |
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| 21 | /* compute magnetic declination for given location, elevation and time.
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| 22 | * sign is such that mag bearing = true az + mag deviation.
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| 23 | * return 0 if ok, -1 if no model file, -2 if time outside model range.
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| 24 | * fill err[] with excuse if return < 0.
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| 25 | */
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| 26 | int
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| 27 | magdecl (
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| 28 | double l, double L, /* geodesic lat, +N, long, +E, rads */
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| 29 | double e, /* elevation, m */
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| 30 | double y, /* time, decimal year */
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| 31 | char *dir, /* dir for model file */
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| 32 | double *mdp, /* magnetic deviation, rads E of N */
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| 33 | char *err) /* err message if return < 0 */
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| 34 | {
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| 35 | float dlat = raddeg(l);
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| 36 | float dlon = raddeg(L);
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| 37 | float alt = e/1000.;
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| 38 | int maxdeg = 12;
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| 39 | float dec, dp, ti, gv;
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| 40 | char mfile[1024];
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| 41 | FILE *wmmdat;
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| 42 | int s;
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| 43 |
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| 44 | /* open model file */
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| 45 | sprintf (mfile, "%s/%s", dir, mfn);
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| 46 | wmmdat = fopen (mfile, "r");
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| 47 | if (!wmmdat) {
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| 48 | sprintf (err, "%s: %s", mfile, strerror(errno));
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| 49 | return (-1);
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| 50 | }
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| 51 |
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| 52 | /* compute deviation */
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| 53 | geomag(wmmdat, &maxdeg);
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| 54 | s = geomg1(wmmdat,alt,dlat,dlon,y,&dec,&dp,&ti,&gv);
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| 55 | fclose(wmmdat);
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| 56 | if (s < 0) {
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| 57 | sprintf (err, "Magnetic model only available for %g .. %g. See http://www.ngdc.noaa.gov", ti, ti+5);
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| 58 | return (-2);
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| 59 | }
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| 60 | *mdp = degrad(dec);
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| 61 | return (0);
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| 62 | }
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| 63 |
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| 64 | #if defined(TEST_MAIN)
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| 65 |
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| 66 | int
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| 67 | main(int ac, char *av[])
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| 68 | {
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| 69 | char err[1024];
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| 70 | float altm, dlat, dlon;
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| 71 | float t;
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| 72 | double dec;
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| 73 |
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| 74 | S1:
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| 75 | printf("\n\n\n ENTER LATITUDE IN DECIMAL DEGREES (+25.0)\n");
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| 76 | scanf("%f", &dlat);
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| 77 |
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| 78 | printf(" ENTER LONGITUDE IN DECIMAL DEGREES (-100.0)\n");
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| 79 | scanf("%f", &dlon);
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| 80 |
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| 81 | printf(" ENTER ALTITUDE IN METERS\n");
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| 82 | scanf("%f", &altm);
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| 83 |
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| 84 | printf(" ENTER TIME IN DECIMAL YEAR\n");
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| 85 | scanf("%f",&t);
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| 86 |
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| 87 | if (magdecl (degrad(dlat), degrad(dlon), altm, t, "auxil", &dec,
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| 88 | err) < 0) {
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| 89 | printf ("%s\n", err);
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| 90 | return(1);
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| 91 | }
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| 92 |
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| 93 | printf("\n LATITUDE: = %-7.2f DEG",dlat);
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| 94 | printf("\n LONGITUDE: = %-7.2f DEG\n",dlon);
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| 95 | printf("\n ALTITUDE = %.2f METERS",altm);
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| 96 | printf("\n DATE = %-5.1f\n",t);
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| 97 |
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| 98 | printf("\n\t\t\t OUTPUT\n\t\t\t ------");
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| 99 |
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| 100 | printf("\n DEC = %-7.2f DEG", raddeg(dec));
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| 101 |
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| 102 | printf("\n\n\n DO YOU NEED MORE POINT DATA? (y or n)\n");
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| 103 | scanf("%s", err);
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| 104 | if ((err[0] =='y')||(err[0] == 'Y')) goto S1;
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| 105 |
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| 106 | return(0);
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| 107 | }
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| 108 | #endif /* defined(TEST_MAIN) */
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| 109 |
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| 110 | /*************************************************************************
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| 111 | * return 0 if ok, -1 if time is out of range with base epoc in *ti
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| 112 | */
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| 113 |
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| 114 | static int E0000(FILE *wmmdat, int IENTRY, int *maxdeg, float alt,
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| 115 | float glat, float glon, float t, float *dec, float *mdp, float *ti,
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| 116 | float *gv)
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| 117 | {
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| 118 | static int maxord,i,icomp,n,m,j,D1,D2,D3,D4;
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| 119 | static float c[13][13],cd[13][13],tc[13][13],dp[13][13],snorm[169],
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| 120 | sp[13],cp[13],fn[13],fm[13],pp[13],k[13][13],pi,dtr,a,b,re,
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| 121 | a2,b2,c2,a4,b4,c4,epoc,gnm,hnm,dgnm,dhnm,flnmj,otime,oalt,
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| 122 | olat,olon,dt,rlon,rlat,srlon,srlat,crlon,crlat,srlat2,
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| 123 | crlat2,q,q1,q2,ct,st,r2,r,d,ca,sa,aor,ar,br,bt,bp,bpp,
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| 124 | par,temp1,temp2,parp,bx,by,bz,bh;
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| 125 | static char model[20], c_str[81], c_new[5];
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| 126 | static float *p = snorm;
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| 127 |
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| 128 | switch(IENTRY){case 0: goto GEOMAG; case 1: goto GEOMG1;}
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| 129 |
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| 130 | GEOMAG:
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| 131 |
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| 132 | /* INITIALIZE CONSTANTS */
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| 133 | maxord = *maxdeg;
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| 134 | sp[0] = 0.0;
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| 135 | cp[0] = *p = pp[0] = 1.0;
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| 136 | dp[0][0] = 0.0;
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| 137 | a = 6378.137;
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| 138 | b = 6356.7523142;
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| 139 | re = 6371.2;
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| 140 | a2 = a*a;
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| 141 | b2 = b*b;
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| 142 | c2 = a2-b2;
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| 143 | a4 = a2*a2;
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| 144 | b4 = b2*b2;
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| 145 | c4 = a4 - b4;
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| 146 |
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| 147 | /* READ WORLD MAGNETIC MODEL SPHERICAL HARMONIC COEFFICIENTS */
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| 148 | c[0][0] = 0.0;
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| 149 | cd[0][0] = 0.0;
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| 150 | fgets(c_str, 80, wmmdat);
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| 151 | sscanf(c_str,"%f%s",&epoc,model);
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| 152 | S3:
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| 153 | fgets(c_str, 80, wmmdat);
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| 154 | /* CHECK FOR LAST LINE IN FILE */
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| 155 | for (i=0; i<4 && (c_str[i] != '\0'); i++)
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| 156 | {
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| 157 | c_new[i] = c_str[i];
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| 158 | c_new[i+1] = '\0';
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| 159 | }
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| 160 | icomp = strcmp("9999", c_new);
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| 161 | if (icomp == 0) goto S4;
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| 162 | /* END OF FILE NOT ENCOUNTERED, GET VALUES */
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| 163 | sscanf(c_str,"%d%d%f%f%f%f",&n,&m,&gnm,&hnm,&dgnm,&dhnm);
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| 164 | if (m <= n)
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| 165 | {
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| 166 | c[m][n] = gnm;
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| 167 | cd[m][n] = dgnm;
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| 168 | if (m != 0)
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| 169 | {
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| 170 | c[n][m-1] = hnm;
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| 171 | cd[n][m-1] = dhnm;
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| 172 | }
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| 173 | }
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| 174 | goto S3;
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| 175 |
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| 176 | /* CONVERT SCHMIDT NORMALIZED GAUSS COEFFICIENTS TO UNNORMALIZED */
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| 177 | S4:
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| 178 | *snorm = 1.0;
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| 179 | for (n=1; n<=maxord; n++)
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| 180 | {
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| 181 | *(snorm+n) = *(snorm+n-1)*(float)(2*n-1)/(float)n;
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| 182 | j = 2;
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| 183 | for (m=0,D1=1,D2=(n-m+D1)/D1; D2>0; D2--,m+=D1)
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| 184 | {
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| 185 | k[m][n] = (float)(((n-1)*(n-1))-(m*m))/(float)((2*n-1)*(2*n-3));
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| 186 | if (m > 0)
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| 187 | {
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| 188 | flnmj = (float)((n-m+1)*j)/(float)(n+m);
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| 189 | *(snorm+n+m*13) = *(snorm+n+(m-1)*13)*sqrt(flnmj);
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| 190 | j = 1;
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| 191 | c[n][m-1] = *(snorm+n+m*13)*c[n][m-1];
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| 192 | cd[n][m-1] = *(snorm+n+m*13)*cd[n][m-1];
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| 193 | }
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| 194 | c[m][n] = *(snorm+n+m*13)*c[m][n];
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| 195 | cd[m][n] = *(snorm+n+m*13)*cd[m][n];
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| 196 | }
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| 197 | fn[n] = (float)(n+1);
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| 198 | fm[n] = (float)n;
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| 199 | }
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| 200 | k[1][1] = 0.0;
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| 201 |
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| 202 | otime = oalt = olat = olon = -1000.0;
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| 203 | return (0);
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| 204 |
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| 205 | /*************************************************************************/
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| 206 |
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| 207 | GEOMG1:
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| 208 |
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| 209 | dt = t - epoc;
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| 210 | if (otime < 0.0 && (dt < 0.0 || dt > 5.0)) {
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| 211 | *ti = epoc; /* pass back base time for diag msg */
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| 212 | return (-1);
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| 213 | }
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| 214 |
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| 215 | pi = 3.14159265359;
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| 216 | dtr = pi/180.0;
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| 217 | rlon = glon*dtr;
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| 218 | rlat = glat*dtr;
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| 219 | srlon = sin(rlon);
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| 220 | srlat = sin(rlat);
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| 221 | crlon = cos(rlon);
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| 222 | crlat = cos(rlat);
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| 223 | srlat2 = srlat*srlat;
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| 224 | crlat2 = crlat*crlat;
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| 225 | sp[1] = srlon;
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| 226 | cp[1] = crlon;
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| 227 |
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| 228 | /* CONVERT FROM GEODETIC COORDS. TO SPHERICAL COORDS. */
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| 229 | if (alt != oalt || glat != olat)
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| 230 | {
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| 231 | q = sqrt(a2-c2*srlat2);
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| 232 | q1 = alt*q;
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| 233 | q2 = ((q1+a2)/(q1+b2))*((q1+a2)/(q1+b2));
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| 234 | ct = srlat/sqrt(q2*crlat2+srlat2);
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| 235 | st = sqrt(1.0-(ct*ct));
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| 236 | r2 = (alt*alt)+2.0*q1+(a4-c4*srlat2)/(q*q);
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| 237 | r = sqrt(r2);
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| 238 | d = sqrt(a2*crlat2+b2*srlat2);
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| 239 | ca = (alt+d)/r;
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| 240 | sa = c2*crlat*srlat/(r*d);
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| 241 | }
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| 242 | if (glon != olon)
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| 243 | {
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| 244 | for (m=2; m<=maxord; m++)
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| 245 | {
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| 246 | sp[m] = sp[1]*cp[m-1]+cp[1]*sp[m-1];
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| 247 | cp[m] = cp[1]*cp[m-1]-sp[1]*sp[m-1];
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| 248 | }
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| 249 | }
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| 250 | aor = re/r;
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| 251 | ar = aor*aor;
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| 252 | br = bt = bp = bpp = 0.0;
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| 253 | for (n=1; n<=maxord; n++)
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| 254 | {
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| 255 | ar = ar*aor;
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| 256 | for (m=0,D3=1,D4=(n+m+D3)/D3; D4>0; D4--,m+=D3)
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| 257 | {
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| 258 | /*
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| 259 | COMPUTE UNNORMALIZED ASSOCIATED LEGENDRE POLYNOMIALS
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| 260 | AND DERIVATIVES VIA RECURSION RELATIONS
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| 261 | */
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| 262 | if (alt != oalt || glat != olat)
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| 263 | {
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| 264 | if (n == m)
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| 265 | {
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| 266 | *(p+n+m*13) = st**(p+n-1+(m-1)*13);
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| 267 | dp[m][n] = st*dp[m-1][n-1]+ct**(p+n-1+(m-1)*13);
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| 268 | goto S50;
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| 269 | }
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| 270 | if (n == 1 && m == 0)
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| 271 | {
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| 272 | *(p+n+m*13) = ct**(p+n-1+m*13);
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| 273 | dp[m][n] = ct*dp[m][n-1]-st**(p+n-1+m*13);
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| 274 | goto S50;
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| 275 | }
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| 276 | if (n > 1 && n != m)
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| 277 | {
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| 278 | if (m > n-2) *(p+n-2+m*13) = 0.0;
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| 279 | if (m > n-2) dp[m][n-2] = 0.0;
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| 280 | *(p+n+m*13) = ct**(p+n-1+m*13)-k[m][n]**(p+n-2+m*13);
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| 281 | dp[m][n] = ct*dp[m][n-1] - st**(p+n-1+m*13)-k[m][n]*dp[m][n-2];
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| 282 | }
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| 283 | }
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| 284 | S50:
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| 285 | /*
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| 286 | TIME ADJUST THE GAUSS COEFFICIENTS
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| 287 | */
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| 288 | if (t != otime)
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| 289 | {
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| 290 | tc[m][n] = c[m][n]+dt*cd[m][n];
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| 291 | if (m != 0) tc[n][m-1] = c[n][m-1]+dt*cd[n][m-1];
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| 292 | }
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| 293 | /*
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| 294 | ACCUMULATE TERMS OF THE SPHERICAL HARMONIC EXPANSIONS
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| 295 | */
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| 296 | par = ar**(p+n+m*13);
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| 297 | if (m == 0)
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| 298 | {
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| 299 | temp1 = tc[m][n]*cp[m];
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| 300 | temp2 = tc[m][n]*sp[m];
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| 301 | }
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| 302 | else
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| 303 | {
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| 304 | temp1 = tc[m][n]*cp[m]+tc[n][m-1]*sp[m];
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| 305 | temp2 = tc[m][n]*sp[m]-tc[n][m-1]*cp[m];
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| 306 | }
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| 307 | bt = bt-ar*temp1*dp[m][n];
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| 308 | bp += (fm[m]*temp2*par);
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| 309 | br += (fn[n]*temp1*par);
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| 310 | /*
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| 311 | SPECIAL CASE: NORTH/SOUTH GEOGRAPHIC POLES
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| 312 | */
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| 313 | if (st == 0.0 && m == 1)
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| 314 | {
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| 315 | if (n == 1) pp[n] = pp[n-1];
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| 316 | else pp[n] = ct*pp[n-1]-k[m][n]*pp[n-2];
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| 317 | parp = ar*pp[n];
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| 318 | bpp += (fm[m]*temp2*parp);
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| 319 | }
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| 320 | }
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| 321 | }
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| 322 | if (st == 0.0) bp = bpp;
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| 323 | else bp /= st;
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| 324 | /*
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| 325 | ROTATE MAGNETIC VECTOR COMPONENTS FROM SPHERICAL TO
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| 326 | GEODETIC COORDINATES
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| 327 | */
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| 328 | bx = -bt*ca-br*sa;
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| 329 | by = bp;
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| 330 | bz = bt*sa-br*ca;
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| 331 | /*
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| 332 | COMPUTE DECLINATION (DEC), INCLINATION (DIP) AND
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| 333 | TOTAL INTENSITY (TI)
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| 334 | */
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| 335 | bh = sqrt((bx*bx)+(by*by));
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| 336 | *ti = sqrt((bh*bh)+(bz*bz));
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| 337 | *dec = atan2(by,bx)/dtr;
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| 338 | *mdp = atan2(bz,bh)/dtr;
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| 339 | /*
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| 340 | COMPUTE MAGNETIC GRID VARIATION IF THE CURRENT
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| 341 | GEODETIC POSITION IS IN THE ARCTIC OR ANTARCTIC
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| 342 | (I.E. GLAT > +55 DEGREES OR GLAT < -55 DEGREES)
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| 343 |
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| 344 | OTHERWISE, SET MAGNETIC GRID VARIATION TO -999.0
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| 345 | */
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| 346 | *gv = -999.0;
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| 347 | if (fabs(glat) >= 55.)
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| 348 | {
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| 349 | if (glat > 0.0 && glon >= 0.0) *gv = *dec-glon;
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| 350 | if (glat > 0.0 && glon < 0.0) *gv = *dec+fabs(glon);
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| 351 | if (glat < 0.0 && glon >= 0.0) *gv = *dec+glon;
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| 352 | if (glat < 0.0 && glon < 0.0) *gv = *dec-fabs(glon);
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| 353 | if (*gv > +180.0) *gv -= 360.0;
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| 354 | if (*gv < -180.0) *gv += 360.0;
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| 355 | }
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| 356 | otime = t;
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| 357 | oalt = alt;
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| 358 | olat = glat;
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| 359 | olon = glon;
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| 360 | return (0);
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| 361 | }
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| 362 |
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| 363 | /*************************************************************************/
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| 364 |
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| 365 | static int
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| 366 | geomag(FILE *wmmdat, int *maxdeg)
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| 367 | {
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| 368 | return (E0000(wmmdat,0,maxdeg,0.0,0.0,0.0,0.0,NULL,NULL,NULL,NULL));
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| 369 | }
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| 370 |
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| 371 | /*************************************************************************/
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| 372 |
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| 373 | static int
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| 374 | geomg1(FILE *wmmdat, float alt, float glat, float glon, float t,
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| 375 | float *dec, float *mdp, float *ti, float *gv)
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| 376 | {
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| 377 | return (E0000(wmmdat,1,NULL,alt,glat,glon,t,dec,mdp,ti,gv));
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| 378 | }
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| 379 |
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| 380 | /* For RCS Only -- Do Not Edit */
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| 381 | static char *rcsid[2] = {(char *)rcsid, "@(#) $RCSfile: magdecl.c,v $ $Date: 2004-06-15 16:54:12 $ $Revision: 1.1 $ $Name: not supported by cvs2svn $"};
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