source: buchla-68k/orig/DATE/SUN.C@ ad89950

/*
   ============================================================================ 
        sun.c -- calculate sunrise, sunset, and position of the sun
        Version 5 -- 1989-01-12 -- Robert Bond / D.N. Lynx Crowe
 
        sun <options>

        options:        -t hh:mm:ss     time (default is current system time)
                        -d mm/dd/yy     date (default is current system date)
                        -a lat          decimal latitude (default = 45.5333)
                        -o lon          decimal longitude (default = 122.8333) 
                        -z tz           timezone (default = 8, pst)
                        -p              show position of sun (azimuth)
        
        All output is to standard io.  

        Compile with cc -O  -o sun -lm

        Define BSD for BSD4.2 systems.  System V assumed otherwise.
        This selects between <sys/time.h> and <time.h> below.

        Note that the latitude, longitude, time zone correction and
        time zone string are all defaulted in the global variable section.
        The default is for Oakland, CA.

        Most of the code in this program is adapted from algorithms
        presented in "Practical Astronomy With Your Calculator" by
        Peter Duffet-Smith.

        The GST and ALT-AZIMUTH algorithms are from Sky and Telescope,
        June, 1984 by Roger W. Sinnott

        Original author: Robert Bond - Beaverton, Oregon.
        Mods by:  D.N. Lynx Crowe - Oakland, California.
   ============================================================================ 
*/

#include "stdio.h"
#include "math.h"
#include "types.h"

#ifdef BSD
#include <sys/time.h>
#else
#include "time.h"
#endif

#ifndef PI
#define PI       3.141592654
#endif

#define EPOCH    1980
#define JDE      2444238.5      /* Julian date of EPOCH */

double dtor();
double adj360();
double adj24();
double julian_date();
double hms_to_dh();
double solar_lon();
double acos_deg();
double asin_deg();
double atan_q_deg();
double atan_deg();
double sin_deg();
double cos_deg();
double tan_deg();
double gmst();

int th;
int tm;
int ts;
int mo;
int day;
int yr;
int popt = 0;

int tz=8;                       /* Default time zone */
char *tzs = "(PST)";            /* Default time zone string */
char *dtzs = "(PDT)";           /* Default daylight savings time string */

/* double lat = 45.5333;                /* Default latitude (Beaverton Ore.) */
/* double lon = 122.8333;               /* Default Longitude (Degrees west) */ 

double lat = 37.75;             /* Default latitude (Oakland, CA) */
double lon = 122.25;            /* Default longitude (degrees west) */

/* 

*/

main(argc,argv)
int argc;
char *argv[];
{
        double ed, jd;
        double alpha1, delta1, alpha2, delta2, st1r, st1s, st2r, st2s;
        double a1r, a1s, a2r, a2s, dt, dh, x, y;
        double trise, tset, ar, as, alpha, delta, tri, da;
        double lambda1, lambda2;
        double alt, az, gst, m1;
        double hsm, ratio;
        time_t sec_1970;
        int h, m;
        struct tm *pt;

        sec_1970 = time((time_t *)0);  
        pt = localtime(&sec_1970);  

        th = pt->tm_hour;
        tm = pt->tm_min;
        ts = pt->tm_sec;
        yr = pt->tm_year + 1900;
        mo = pt->tm_mon + 1;
        day = pt->tm_mday;

        if (pt->tm_isdst) {             /* convert tz to daylight savings time */

                tz--;
                tzs = dtzs;     
        }

        initopts(argc,argv);

        printf("On %04d-%02d-%02d at %02d:%02d:%02d\n",
                yr, mo, day, th, tm, ts);

        jd = julian_date(mo,day,yr);
        ed = jd - JDE;

        lambda1 = solar_lon(ed);
        lambda2 = solar_lon(ed + 1.0);

        lon_to_eq(lambda1, &alpha1, &delta1);
        lon_to_eq(lambda2, &alpha2, &delta2);

        rise_set(alpha1, delta1, &st1r, &st1s, &a1r, &a1s);
        rise_set(alpha2, delta2, &st2r, &st2s, &a2r, &a2s);

        m1 = adj24(gmst(jd - 0.5, 0.5 + tz / 24.0) - lon / 15); /* lst midnight */
        hsm = adj24(st1r - m1);
        ratio = hsm / 24.07;

        if (fabs(st2r - st1r) > 1.0) {

                st2r += 24.0;
        }

        trise = adj24((1.0 - ratio) * st1r + ratio * st2r);

        hsm = adj24(st1s - m1);
        ratio = hsm / 24.07;

        if (fabs(st2s - st1s) > 1.0) {

                st2s += 24.0;
        }

        tset = adj24((1.0 - ratio) * st1s + ratio * st2s);

        ar = a1r * 360.0 / (360.0 + a1r - a2r);
        as = a1s * 360.0 / (360.0 + a1s - a2s);

        delta = (delta1 + delta2) / 2.0;
        tri = acos_deg(sin_deg(lat)/cos_deg(delta));

        x = 0.835608;   /* correction for refraction, parallax, size of sun */
        y = asin_deg(sin_deg(x)/sin_deg(tri));
        da = asin_deg(tan_deg(x)/tan_deg(tri));
        dt = 240.0 * y / cos_deg(delta) / 3600;

        lst_to_hm(trise - dt, jd, &h, &m);
        printf("Sunrise: %2d:%02d    ", h, m);

        if (popt) {

                dh_to_hm(ar - da, &h, &m);
                printf("Azimuth: %2d deg %02d min \n", h, m);
        }

        lst_to_hm(tset + dt, jd, &h, &m);
        printf("Sunset:  %2d:%02d    ", h, m);

        if (popt) {

                dh_to_hm(as + da, &h, &m);
                printf("Azimuth: %2d deg %02d min \n", h, m);

        } else 
                printf("%s \n",tzs);

        if (popt) {

                if (alpha1 < alpha2)
                        alpha = (alpha1 + alpha2) / 2.0;
                else
                        alpha = (alpha1 + 24.0 + alpha2) / 2.0;
        
                if (alpha > 24.0)
                        alpha -= 24.0;

                dh = (hms_to_dh(th, tm, ts) + tz) / 24.0;

                if (dh > 0.5) {

                        dh -= 0.5;
                        jd += 0.5;

                } else {

                        dh += 0.5;
                        jd -= 0.5;
                }

                gst = gmst(jd, dh);

                eq_to_altaz(alpha, delta, gst, &alt, &az);

                printf("The sun is at ");
                dh_to_hm(alt, &h, &m);
                printf("Altitude: %2d deg %02d min", h, m);
                dh_to_hm(az, &h, &m);
                printf("   Azimuth:  %2d deg %02d min. \n", h, m);
        }
}

/* 

*/

double
dtor(deg)
double deg;
{
        return (deg * PI / 180.0);
}

double
rtod(deg)
double deg;
{
        return (deg * 180.0 / PI);
}


double
adj360(deg)
double deg;
{
        while (deg < 0.0) 
                deg += 360.0;

        while (deg > 360.0)
                deg -= 360.0;

        return(deg);
}

double
adj24(hrs)
double hrs;
{
        while (hrs < 0.0) 
                hrs += 24.0;

        while (hrs > 24.0)
                hrs -= 24.0;

        return(hrs);
}

/* 

*/

initopts(argc,argv)
int argc;
char *argv[];
{
        int ai;
        char *ca;
        char *str;

        while (--argc) {

                if ((*++argv)[0] == '-') {

                        ca = *argv;

                        for(ai = 1; ca[ai] != '\0'; ai++)
                                switch (ca[ai]) {

                                case 'p':
                                        popt++;
                                        break;

                                case 'a':
                                        str = *++argv;
                
                                        if (sscanf(str, "%lf", &lat) != 1)
                                                usage();

                                        argc--;
                                        break;

                                case 'o':
                                        str = *++argv;

                                        if (sscanf(str, "%lf", &lon) != 1)
                                                usage();

                                        argc--;
                                        break;

                                case 'z':
                                        str = *++argv;

                                        if (sscanf(str, "%d", &tz) != 1)
                                                usage();

                                        tzs = "   ";
                                        argc--;
                                        break;

                                case 't':
                                        str = *++argv;

                                        if (sscanf(str, "%d:%d:%d", &th, &tm, &ts) != 3)
                                                usage();

                                        argc--;
                                        break;

                                case 'd':
                                        str = *++argv;

                                        if (sscanf(str, "%d/%d/%d", &mo, &day, &yr) != 3)
                                                usage();

                                        argc--;
                                        break;

                                default:
                                        usage();
                                }

                } else
                        usage();
        }
}

/* 

*/

usage()
{
        printf("Usage: sun [-p] [-t h:m:s] [-d m/d/y] [-a lat] [-o lon] [-z tz]\n");

        printf("-p\t\tshow position of sun (azimuth)\n");
        printf("-t hh:mm:ss\ttime (default is current system time)\n");
        printf("-d mm/dd/yy\tdate (default is current system date)\n");
        printf("-a lat\t\tdecimal latitude (default = 37.75)\n");
        printf("-o lon\t\tdecimal longitude (default = 122.25) \n");
        printf("-z tz\t\ttimezone (default = 8, pst)\n");
        printf("\nDefaults are for Oakland, CA\n");
        exit(1);
}

/* 

*/

double
julian_date(m, d, y)
{
        int a, b;
        double jd;

        if (m == 1 || m == 2) {

                --y;
                m += 12;
        }

        if (y < 1583) {

                printf("Can't handle dates before 1583 \n");
                exit(1);
        }

        a = y/100;
        b = 2 - a + a/4;
        b += (int)((double)y * 365.25);
        b += (int)(30.6001 * ((double)m + 1.0));
        jd = (double)d + (double)b + 1720994.5;
        return(jd);
}

double
hms_to_dh(h, m, s)
{
        double rv;

        rv = h + m / 60.0 + s / 3600.0;
        return rv;
}

/* 

*/

double
solar_lon(ed)
double ed;
{
        double n, m, e, ect, errt, v;

        n = 360.0 * ed / 365.2422;
        n = adj360(n);
        m = n + 278.83354 - 282.596403;
        m = adj360(m);
        m = dtor(m);
        e = m; ect = 0.016718;

        while ((errt = e - ect * sin(e) - m) > 0.0000001) 
                e = e - errt / (1 - ect * cos(e));

        v = 2 * atan(1.0168601 * tan(e/2));
        v = adj360(v * 180.0 / PI + 282.596403);
        return(v);
}

/* 

*/

double
acos_deg(x)
double x;
{
        return rtod(acos(x));
}

double
asin_deg(x)
double x;
{
        return rtod(asin(x));
}

double
atan_q_deg(y,x)
double y,x;
{
        double rv;

        if (y == 0)
                rv = 0;
        else if (x == 0)
                rv = y>0 ? 90.0 : -90.0;
        else
                rv = atan_deg(y/x);

        if (x<0)
                return rv+180.0;

        if (y<0)
                return rv+360.0;

        return(rv);
}

/* 

*/

double
atan_deg(x)
double x;
{
        return rtod(atan(x));
}

double
sin_deg(x)
double x;
{
        return sin(dtor(x));
}

double
cos_deg(x)
double x;
{
        return cos(dtor(x));
}

double
tan_deg(x)
double x;
{
        return tan(dtor(x));
}

/* 

*/

lon_to_eq(lambda, alpha, delta)
double lambda;
double *alpha;
double *delta;
{
        double tlam,epsilon;

        tlam = dtor(lambda);
        epsilon = dtor((double)23.441884);
        *alpha = atan_q_deg((sin(tlam))*cos(epsilon),cos(tlam)) / 15.0;
        *delta = asin_deg(sin(epsilon)*sin(tlam));
}

rise_set(alpha, delta, lstr, lsts, ar, as)
double alpha, delta, *lstr, *lsts, *ar, *as;
{
        double tar;
        double h;

        tar = sin_deg(delta)/cos_deg(lat);

        if (tar < -1.0 || tar > 1.0) {

                printf("The object is circumpolar \n");
                exit (1);
        }

        *ar = acos_deg(tar);
        *as = 360.0 - *ar;

        h = acos_deg(-tan_deg(lat) * tan_deg(delta)) / 15.0;
        *lstr = 24.0 + alpha - h;

        if (*lstr > 24.0)
                *lstr -= 24.0;

        *lsts = alpha + h;

        if (*lsts > 24.0)
                *lsts -= 24.0;
}

/* 

*/

lst_to_hm(lst, jd, h, m)
double lst, jd;
int *h, *m;
{
        double ed, gst, jzjd, t, r, b, t0, gmt;

        gst = lst + lon / 15.0;

        if (gst > 24.0)
                gst -= 24.0;

        jzjd = julian_date(1,0,yr);
        ed = jd-jzjd;
        t = (jzjd -2415020.0)/36525.0;
        r = 6.6460656+2400.05126*t+2.58E-05*t*t;
        b = 24-(r-24*(yr-1900));
        t0 = ed * 0.0657098 - b;

        if (t0 < 0.0)
                t0 += 24;

        gmt = gst-t0;

        if (gmt<0) 
                gmt += 24.0;

        gmt = gmt * 0.99727 - tz;;

        if (gmt < 0)
                gmt +=24.0;

        dh_to_hm(gmt, h, m);
}

/* 

*/

dh_to_hm(dh, h, m)
double dh;
int *h, *m;
{
        double tempsec;

        *h = dh;
        *m = (dh - *h) * 60;
        tempsec = (dh - *h) * 60 - *m;
        tempsec = tempsec * 60 + 0.5;

        if (tempsec > 30)
                (*m)++;

        if (*m == 60) {

                *m = 0;
                (*h)++;
        }
}

/* 

*/

eq_to_altaz(r, d, t, alt, az)
double r, d, t;
double *alt, *az;
{
        double p = 3.14159265;
        double r1 = p / 180.0;
        double b = lat * r1;
        double l = (360 - lon) * r1;
        double t5, s1, c1, c2, s2, a, h;

        r = r * 15.0 * r1;
        d = d * r1;
        t = t * 15.0 * r1;
        t5 = t - r + l;
        s1 = sin(b) * sin(d) + cos(b) * cos(d) * cos(t5);
        c1 = 1 - s1 * s1;

        if (c1 > 0) {

                c1 = sqrt(c1);
                h = atan(s1 / c1);

        } else {

                h = (s1 / fabs(s1)) * (p / 2.0);
        }

        c2 = cos(b) * sin(d) - sin(b) * cos(d) * cos(t5);
        s2 = -cos(d) * sin(t5);

        if (c2 == 0) 
                a = (s2/fabs(s2)) * (p/2);
        else {

        a = atan(s2/c2);

                if (c2 < 0)
                        a=a+p;
        }

        if (a<0)
                a=a+2*p;

        *alt = h / r1;
        *az = a / r1;
}

/* 

*/

double
gmst(j, f)
double j,f;
{
        double d, j0, t, t1, t2, s;

        d = j - 2451545.0;
        t = d / 36525.0;
        t1 = floor(t);
        j0 = t1 * 36525.0 + 2451545.0;
        t2 = (j - j0 + 0.5)/36525.0;
        s = 24110.54841 + 184.812866 * t1; 
        s += 8640184.812866 * t2;
        s += 0.093104 * t * t;
        s -= 0.0000062 * t * t * t;
        s /= 86400.0;
        s -= floor(s);
        s = 24 * (s + (f - 0.5) * 1.002737909);

        if (s < 0)
                s += 24.0;

        if (s > 24.0)
                s -= 24.0;

        return(s);
}