src/gen/gensky.c

/* Copyright (c) 1992 Regents of the University of California */

#ifndef lint
static char SCCSid[] = "$SunId$ LBL";
#endif

/*
 *  gensky.c - program to generate sky functions.
 *              Our zenith is along the Z-axis, the X-axis
 *              points east, and the Y-axis points north.
 *              Radiance is in watts/steradian/sq. meter.
 *
 *     3/26/86
 */

#include  <stdio.h>

#include  <math.h>

#include  <ctype.h>

#include  "color.h"

extern char  *strcpy(), *strcat(), *malloc();
extern double  stadj(), sdec(), sazi(), salt(), tz2mer();

#ifndef  PI
#define  PI             3.14159265358979323846
#endif

#define  DOT(v1,v2)     (v1[0]*v2[0]+v1[1]*v2[1]+v1[2]*v2[2])

#define  S_CLEAR        1
#define  S_OVER         2
#define  S_UNIF         3
#define  S_INTER        4

#define  overcast       (skytype==S_OVER|skytype==S_UNIF)

double  normsc();
                                        /* sun calculation constants */
extern double  s_latitude;
extern double  s_longitude;
extern double  s_meridian;

#undef  toupper
#define  toupper(c)     ((c) & ~0x20)   /* ASCII trick to convert case */

                                        /* European and North American zones */
struct {
        char    zname[8];       /* time zone name (all caps) */
        float   zmer;           /* standard meridian */
} tzone[] = {
        "YST", 135, "YDT", 120,
        "PST", 120, "PDT", 105,
        "MST", 105, "MDT", 90,
        "CST", 90, "CDT", 75,
        "EST", 75, "EDT", 60,
        "AST", 60, "ADT", 45,
        "NST", 52.5, "NDT", 37.5,
        "GMT", 0, "BST", -15,
        "WET", -15, "WETDST", -30,
        "MET", -30, "METDST", -45,
        "MEZ", -30, "MESZ", -45,
        "", 0
};
                                        /* required values */
int  month, day;                                /* date */
double  hour;                                   /* time */
int  tsolar;                                    /* 0=standard, 1=solar */
double  altitude, azimuth;                      /* or solar angles */
                                        /* default values */
int  skytype = S_CLEAR;                         /* sky type */
int  dosun = 1;
double  zenithbr = 0.0;
int     u_zenith = 0;                           /* -1=irradiance, 1=radiance */
double  turbidity = 2.75;
double  gprefl = 0.2;
                                        /* computed values */
double  sundir[3];
double  groundbr;
double  F2;
double  solarbr = 0.0;
int     u_solar = 0;                            /* -1=irradiance, 1=radiance */

char  *progname;
char  errmsg[128];


main(argc, argv)
int  argc;
char  *argv[];
{
        int  i;

        progname = argv[0];
        if (argc == 2 && !strcmp(argv[1], "-defaults")) {
                printdefaults();
                exit(0);
        }
        if (argc < 4)
                userror("arg count");
        if (!strcmp(argv[1], "-ang")) {
                altitude = atof(argv[2]) * (PI/180);
                azimuth = atof(argv[3]) * (PI/180);
                month = 0;
        } else {
                month = atoi(argv[1]);
                if (month < 1 || month > 12)
                        userror("bad month");
                day = atoi(argv[2]);
                if (day < 1 || day > 31)
                        userror("bad day");
                cvthour(argv[3]);
        }
        for (i = 4; i < argc; i++)
                if (argv[i][0] == '-' || argv[i][0] == '+')
                        switch (argv[i][1]) {
                        case 's':
                                skytype = S_CLEAR;
                                dosun = argv[i][0] == '+';
                                break;
                        case 'r':
                        case 'R':
                                u_solar = argv[i][1]=='R' ? -1 : 1;
                                solarbr = atof(argv[++i]);
                                break;
                        case 'c':
                                skytype = S_OVER;
                                break;
                        case 'u':
                                skytype = S_UNIF;
                                break;
                        case 'i':
                                skytype = S_INTER;
                                dosun = argv[i][0] == '+';
                                break;
                        case 't':
                                turbidity = atof(argv[++i]);
                                break;
                        case 'b':
                        case 'B':
                                u_zenith = argv[i][1]=='B' ? -1 : 1;
                                zenithbr = atof(argv[++i]);
                                break;
                        case 'g':
                                gprefl = atof(argv[++i]);
                                break;
                        case 'a':
                                s_latitude = atof(argv[++i]) * (PI/180);
                                break;
                        case 'o':
                                s_longitude = atof(argv[++i]) * (PI/180);
                                break;
                        case 'm':
                                s_meridian = atof(argv[++i]) * (PI/180);
                                break;
                        default:
                                sprintf(errmsg, "unknown option: %s", argv[i]);
                                userror(errmsg);
                        }
                else
                        userror("bad option");

        if (fabs(s_meridian-s_longitude) > 45*PI/180)
                fprintf(stderr,
        "%s: warning: %.1f hours btwn. standard meridian and longitude\n",
                        progname, (s_longitude-s_meridian)*12/PI);

        printhead(argc, argv);

        computesky();
        printsky();

        exit(0);
}


computesky()                    /* compute sky parameters */
{
        double  normfactor;
                                        /* compute solar direction */
        if (month) {                    /* from date and time */
                int  jd;
                double  sd, st;

                jd = jdate(month, day);         /* Julian date */
                sd = sdec(jd);                  /* solar declination */
                if (tsolar)                     /* solar time */
                        st = hour;
                else
                        st = hour + stadj(jd);
                altitude = salt(sd, st);
                azimuth = sazi(sd, st);
                printf("# Local solar time: %.2f\n", st);
                printf("# Solar altitude and azimuth: %.1f %.1f\n",
                                180./PI*altitude, 180./PI*azimuth);
        }
        if (!overcast && altitude > 87.*PI/180.) {
                fprintf(stderr,
"%s: warning - sun too close to zenith, reducing altitude to 87 degrees\n",
                                progname);
                printf(
"# warning - sun too close to zenith, reducing altitude to 87 degrees\n");
                altitude = 87.*PI/180.;
        }
        sundir[0] = -sin(azimuth)*cos(altitude);
        sundir[1] = -cos(azimuth)*cos(altitude);
        sundir[2] = sin(altitude);

                                        /* Compute normalization factor */
        switch (skytype) {
        case S_UNIF:
                normfactor = 1.0;
                break;
        case S_OVER:
                normfactor = 0.777778;
                break;
        case S_CLEAR:
                F2 = 0.274*(0.91 + 10.0*exp(-3.0*(PI/2.0-altitude)) +
                                0.45*sundir[2]*sundir[2]);
                normfactor = normsc()/F2/PI;
                break;
        case S_INTER:
                F2 = (2.739 + .9891*sin(.3119+2.6*altitude)) *
                        exp(-(PI/2.0-altitude)*(.4441+1.48*altitude));
                normfactor = normsc()/F2/PI;
                break;
        }
                                        /* Compute zenith brightness */
        if (u_zenith == -1)
                zenithbr /= normfactor*PI;
        else if (u_zenith == 0) {
                if (overcast)
                        zenithbr = 8.6*sundir[2] + .123;
                else
                        zenithbr = (1.376*turbidity-1.81)*tan(altitude)+0.38;
                if (skytype == S_INTER)
                        zenithbr = (zenithbr + 8.6*sundir[2] + .123)/2.0;
                if (zenithbr < 0.0)
                        zenithbr = 0.0;
                else
                        zenithbr *= 1000.0/SKYEFFICACY;
        }
                                        /* Compute horizontal radiance */
        groundbr = zenithbr*normfactor;
        printf("# Ground ambient level: %.1f\n", groundbr);
        if (!overcast && sundir[2] > 0.0 && (!u_solar || solarbr > 0.0)) {
                if (u_solar == -1)
                        solarbr /= 6e-5*sundir[2];
                else if (u_solar == 0) {
                        solarbr = 1.5e9/SUNEFFICACY *
                        (1.147 - .147/(sundir[2]>.16?sundir[2]:.16));
                        if (skytype == S_INTER)
                                solarbr *= 0.15;        /* fudge factor! */
                }
                groundbr += 6e-5/PI*solarbr*sundir[2];
        } else
                dosun = 0;
        groundbr *= gprefl;
}


printsky()                      /* print out sky */
{
        if (dosun) {
                printf("\nvoid light solar\n");
                printf("0\n0\n");
                printf("3 %.2e %.2e %.2e\n", solarbr, solarbr, solarbr);
                printf("\nsolar source sun\n");
                printf("0\n0\n");
                printf("4 %f %f %f 0.5\n", sundir[0], sundir[1], sundir[2]);
        }
        
        printf("\nvoid brightfunc skyfunc\n");
        printf("2 skybr skybright.cal\n");
        printf("0\n");
        if (overcast)
                printf("3 %d %.2e %.2e\n", skytype, zenithbr, groundbr);
        else
                printf("7 %d %.2e %.2e %.2e %f %f %f\n",
                                skytype, zenithbr, groundbr, F2,
                                sundir[0], sundir[1], sundir[2]);
}


printdefaults()                 /* print default values */
{
        switch (skytype) {
        case S_OVER:
                printf("-c\t\t\t\t# Cloudy sky\n");
                break;
        case S_UNIF:
                printf("-u\t\t\t\t# Uniform cloudy sky\n");
                break;
        case S_INTER:
                if (dosun)
                        printf("+i\t\t\t\t# Intermediate sky with sun\n");
                else
                        printf("-i\t\t\t\t# Intermediate sky without sun\n");
                break;
        case S_CLEAR:
                if (dosun)
                        printf("+s\t\t\t\t# Sunny sky with sun\n");
                else
                        printf("-s\t\t\t\t# Sunny sky without sun\n");
                break;
        }
        printf("-g %f\t\t\t# Ground plane reflectance\n", gprefl);
        if (zenithbr > 0.0)
                printf("-b %f\t\t\t# Zenith radiance (watts/ster/m2\n", zenithbr);
        else
                printf("-t %f\t\t\t# Atmospheric turbidity\n", turbidity);
        printf("-a %f\t\t\t# Site latitude (degrees)\n", s_latitude*(180/PI));
        printf("-o %f\t\t\t# Site longitude (degrees)\n", s_longitude*(180/PI));
        printf("-m %f\t\t\t# Standard meridian (degrees)\n", s_meridian*(180/PI));
}


userror(msg)                    /* print usage error and quit */
char  *msg;
{
        if (msg != NULL)
                fprintf(stderr, "%s: Use error - %s\n", progname, msg);
        fprintf(stderr, "Usage: %s month day hour [options]\n", progname);
        fprintf(stderr, "   Or: %s -ang altitude azimuth [options]\n", progname);
        fprintf(stderr, "   Or: %s -defaults\n", progname);
        exit(1);
}


double
normsc()                        /* compute normalization factor (E0*F2/L0) */
{
        static double  nfc[2][5] = {
                                /* clear sky approx. */
                {2.766521, 0.547665, -0.369832, 0.009237, 0.059229},
                                /* intermediate sky approx. */
                {3.5556, -2.7152, -1.3081, 1.0660, 0.60227},
        };
        register double  *nf;
        double  x, nsc;
        register int  i;
                                        /* polynomial approximation */
        nf = nfc[skytype==S_INTER];
        x = (altitude - PI/4.0)/(PI/4.0);
        nsc = nf[i=4];
        while (i--)
                nsc = nsc*x + nf[i];

        return(nsc);
}


cvthour(hs)                     /* convert hour string */
char  *hs;
{
        register char  *cp = hs;
        register int    i, j;

        if (tsolar = *cp == '+') cp++;          /* solar time? */
        while (isdigit(*cp)) cp++;
        if (*cp == ':')
                hour = atoi(hs) + atoi(++cp)/60.0;
        else {
                hour = atof(hs);
                if (*cp == '.') cp++;
        }
        while (isdigit(*cp)) cp++;
        if (!*cp)
                return;
        if (tsolar || !isalpha(*cp)) {
                fprintf(stderr, "%s: bad time format: %s\n", progname, hs);
                exit(1);
        }
        i = 0;
        do {
                for (j = 0; cp[j]; j++)
                        if (toupper(cp[j]) != tzone[i].zname[j])
                                break;
                if (!cp[j] && !tzone[i].zname[j]) {
                        s_meridian = tzone[i].zmer * (PI/180);
                        return;
                }
        } while (tzone[i++].zname[0]);

        fprintf(stderr, "%s: unknown time zone: %s\n", progname, cp);
        fprintf(stderr, "Known time zones:\n\t%s", tzone[0].zname);
        for (i = 1; tzone[i].zname[0]; i++)
                fprintf(stderr, " %s", tzone[i].zname);
        putc('\n', stderr);
        exit(1);
}


printhead(ac, av)               /* print command header */
register int  ac;
register char  **av;
{
        putchar('#');
        while (ac--) {
                putchar(' ');
                fputs(*av++, stdout);
        }
        putchar('\n');
}
Revision:	2.18
Committed:	Thu Jul 18 18:00:51 1996 UTC (29 years, 3 months ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 2.17:	+1 -1 lines
Log Message:	changed panic at standard time difference from 2 to 3 hours
#	User	Rev	Content
1	greg	2.9	/* Copyright (c) 1992 Regents of the University of California */
2	greg	1.1
3			#ifndef lint
4			static char SCCSid[] = "$SunId$ LBL";
5			#endif
6
7			/*
8			* gensky.c - program to generate sky functions.
9			* Our zenith is along the Z-axis, the X-axis
10			* points east, and the Y-axis points north.
11			* Radiance is in watts/steradian/sq. meter.
12			*
13			* 3/26/86
14			*/
15
16			#include <stdio.h>
17
18			#include <math.h>
19
20	greg	2.17	#include <ctype.h>
21
22	greg	1.6	#include "color.h"
23	greg	1.1
24			extern char strcpy(), strcat(), *malloc();
25	greg	2.17	extern double stadj(), sdec(), sazi(), salt(), tz2mer();
26	greg	1.1
27	greg	2.17	#ifndef PI
28			#define PI 3.14159265358979323846
29			#endif
30	greg	1.1
31			#define DOT(v1,v2) (v1[0]v2[0]+v1[1]v2[1]+v1[2]*v2[2])
32
33	greg	2.13	#define S_CLEAR 1
34			#define S_OVER 2
35			#define S_UNIF 3
36			#define S_INTER 4
37
38			#define overcast (skytype==S_OVER\|skytype==S_UNIF)
39
40	greg	1.1	double normsc();
41			/* sun calculation constants */
42			extern double s_latitude;
43			extern double s_longitude;
44			extern double s_meridian;
45	greg	2.17
46			#undef toupper
47			#define toupper(c) ((c) & ~0x20) /* ASCII trick to convert case */
48
49			/* European and North American zones */
50			struct {
51			char zname[8]; /* time zone name (all caps) */
52			float zmer; /* standard meridian */
53			} tzone[] = {
54			"YST", 135, "YDT", 120,
55			"PST", 120, "PDT", 105,
56			"MST", 105, "MDT", 90,
57			"CST", 90, "CDT", 75,
58			"EST", 75, "EDT", 60,
59			"AST", 60, "ADT", 45,
60			"NST", 52.5, "NDT", 37.5,
61			"GMT", 0, "BST", -15,
62			"WET", -15, "WETDST", -30,
63			"MET", -30, "METDST", -45,
64			"MEZ", -30, "MESZ", -45,
65			"", 0
66			};
67	greg	1.1	/* required values */
68	greg	2.3	int month, day; /* date */
69	greg	2.5	double hour; /* time */
70			int tsolar; /* 0=standard, 1=solar */
71	greg	2.3	double altitude, azimuth; /* or solar angles */
72	greg	1.1	/* default values */
73	greg	2.13	int skytype = S_CLEAR; /* sky type */
74	greg	1.1	int dosun = 1;
75	greg	2.12	double zenithbr = 0.0;
76			int u_zenith = 0; /* -1=irradiance, 1=radiance */
77	greg	1.1	double turbidity = 2.75;
78			double gprefl = 0.2;
79			/* computed values */
80			double sundir[3];
81			double groundbr;
82			double F2;
83	greg	2.12	double solarbr = 0.0;
84			int u_solar = 0; /* -1=irradiance, 1=radiance */
85	greg	1.1
86			char *progname;
87			char errmsg[128];
88
89
90			main(argc, argv)
91			int argc;
92			char *argv[];
93			{
94			int i;
95
96			progname = argv[0];
97			if (argc == 2 && !strcmp(argv[1], "-defaults")) {
98			printdefaults();
99			exit(0);
100			}
101			if (argc < 4)
102			userror("arg count");
103	greg	2.3	if (!strcmp(argv[1], "-ang")) {
104			altitude = atof(argv[2]) * (PI/180);
105			azimuth = atof(argv[3]) * (PI/180);
106			month = 0;
107			} else {
108			month = atoi(argv[1]);
109	greg	2.6	if (month < 1 \|\| month > 12)
110			userror("bad month");
111	greg	2.3	day = atoi(argv[2]);
112	greg	2.6	if (day < 1 \|\| day > 31)
113			userror("bad day");
114	greg	2.16	cvthour(argv[3]);
115	greg	2.3	}
116	greg	1.1	for (i = 4; i < argc; i++)
117			if (argv[i][0] == '-' \|\| argv[i][0] == '+')
118			switch (argv[i][1]) {
119			case 's':
120	greg	2.13	skytype = S_CLEAR;
121	greg	1.1	dosun = argv[i][0] == '+';
122			break;
123	greg	2.8	case 'r':
124	greg	2.12	case 'R':
125			u_solar = argv[i][1]=='R' ? -1 : 1;
126	greg	2.8	solarbr = atof(argv[++i]);
127			break;
128	greg	1.1	case 'c':
129	greg	2.13	skytype = S_OVER;
130	greg	1.1	break;
131	greg	2.13	case 'u':
132			skytype = S_UNIF;
133			break;
134			case 'i':
135			skytype = S_INTER;
136			dosun = argv[i][0] == '+';
137			break;
138	greg	1.1	case 't':
139			turbidity = atof(argv[++i]);
140			break;
141			case 'b':
142	greg	2.12	case 'B':
143			u_zenith = argv[i][1]=='B' ? -1 : 1;
144	greg	1.1	zenithbr = atof(argv[++i]);
145			break;
146			case 'g':
147			gprefl = atof(argv[++i]);
148			break;
149			case 'a':
150			s_latitude = atof(argv[++i]) * (PI/180);
151			break;
152			case 'o':
153			s_longitude = atof(argv[++i]) * (PI/180);
154			break;
155			case 'm':
156			s_meridian = atof(argv[++i]) * (PI/180);
157			break;
158			default:
159			sprintf(errmsg, "unknown option: %s", argv[i]);
160			userror(errmsg);
161			}
162			else
163			userror("bad option");
164	greg	1.5
165	greg	2.18	if (fabs(s_meridian-s_longitude) > 45*PI/180)
166	greg	1.5	fprintf(stderr,
167			"%s: warning: %.1f hours btwn. standard meridian and longitude\n",
168			progname, (s_longitude-s_meridian)*12/PI);
169	greg	1.1
170			printhead(argc, argv);
171
172			computesky();
173			printsky();
174	greg	2.15
175			exit(0);
176	greg	1.1	}
177
178
179			computesky() /* compute sky parameters */
180			{
181	greg	2.12	double normfactor;
182	greg	1.1	/* compute solar direction */
183	greg	2.3	if (month) { /* from date and time */
184			int jd;
185			double sd, st;
186
187			jd = jdate(month, day); /* Julian date */
188			sd = sdec(jd); /* solar declination */
189	greg	2.5	if (tsolar) /* solar time */
190			st = hour;
191			else
192			st = hour + stadj(jd);
193	greg	2.3	altitude = salt(sd, st);
194			azimuth = sazi(sd, st);
195	greg	2.17	printf("# Local solar time: %.2f\n", st);
196	greg	2.13	printf("# Solar altitude and azimuth: %.1f %.1f\n",
197	greg	2.11	180./PIaltitude, 180./PIazimuth);
198	greg	2.9	}
199	greg	2.13	if (!overcast && altitude > 87.*PI/180.) {
200	greg	2.9	fprintf(stderr,
201			"%s: warning - sun too close to zenith, reducing altitude to 87 degrees\n",
202			progname);
203			printf(
204			"# warning - sun too close to zenith, reducing altitude to 87 degrees\n");
205			altitude = 87.*PI/180.;
206	greg	2.3	}
207	greg	1.1	sundir[0] = -sin(azimuth)*cos(altitude);
208			sundir[1] = -cos(azimuth)*cos(altitude);
209			sundir[2] = sin(altitude);
210
211	greg	2.12	/* Compute normalization factor */
212	greg	2.13	switch (skytype) {
213			case S_UNIF:
214	greg	2.12	normfactor = 1.0;
215	greg	2.13	break;
216			case S_OVER:
217	greg	2.12	normfactor = 0.777778;
218	greg	2.13	break;
219			case S_CLEAR:
220	greg	2.12	F2 = 0.274(0.91 + 10.0exp(-3.0*(PI/2.0-altitude)) +
221			0.45sundir[2]sundir[2]);
222	greg	2.13	normfactor = normsc()/F2/PI;
223			break;
224			case S_INTER:
225			F2 = (2.739 + .9891sin(.3119+2.6altitude)) *
226			exp(-(PI/2.0-altitude)(.4441+1.48altitude));
227			normfactor = normsc()/F2/PI;
228			break;
229	greg	2.12	}
230	greg	1.1	/* Compute zenith brightness */
231	greg	2.12	if (u_zenith == -1)
232			zenithbr /= normfactor*PI;
233			else if (u_zenith == 0) {
234	greg	2.13	if (overcast)
235	greg	1.1	zenithbr = 8.6*sundir[2] + .123;
236	greg	2.12	else
237	greg	1.1	zenithbr = (1.376turbidity-1.81)tan(altitude)+0.38;
238	greg	2.13	if (skytype == S_INTER)
239			zenithbr = (zenithbr + 8.6*sundir[2] + .123)/2.0;
240	greg	2.12	if (zenithbr < 0.0)
241			zenithbr = 0.0;
242			else
243	greg	1.6	zenithbr *= 1000.0/SKYEFFICACY;
244	greg	2.12	}
245	greg	1.1	/* Compute horizontal radiance */
246	greg	2.12	groundbr = zenithbr*normfactor;
247	greg	2.13	printf("# Ground ambient level: %.1f\n", groundbr);
248	greg	2.14	if (!overcast && sundir[2] > 0.0 && (!u_solar \|\| solarbr > 0.0)) {
249	greg	2.12	if (u_solar == -1)
250			solarbr /= 6e-5*sundir[2];
251	greg	2.13	else if (u_solar == 0) {
252	greg	2.12	solarbr = 1.5e9/SUNEFFICACY *
253			(1.147 - .147/(sundir[2]>.16?sundir[2]:.16));
254	greg	2.13	if (skytype == S_INTER)
255			solarbr = 0.15; / fudge factor! */
256			}
257	greg	2.12	groundbr += 6e-5/PIsolarbrsundir[2];
258			} else
259			dosun = 0;
260	greg	1.1	groundbr *= gprefl;
261			}
262
263
264			printsky() /* print out sky */
265			{
266			if (dosun) {
267			printf("\nvoid light solar\n");
268			printf("0\n0\n");
269	greg	1.6	printf("3 %.2e %.2e %.2e\n", solarbr, solarbr, solarbr);
270	greg	1.1	printf("\nsolar source sun\n");
271			printf("0\n0\n");
272			printf("4 %f %f %f 0.5\n", sundir[0], sundir[1], sundir[2]);
273			}
274
275			printf("\nvoid brightfunc skyfunc\n");
276	greg	2.13	printf("2 skybr skybright.cal\n");
277	greg	1.1	printf("0\n");
278	greg	2.13	if (overcast)
279			printf("3 %d %.2e %.2e\n", skytype, zenithbr, groundbr);
280	greg	1.1	else
281	greg	2.13	printf("7 %d %.2e %.2e %.2e %f %f %f\n",
282			skytype, zenithbr, groundbr, F2,
283			sundir[0], sundir[1], sundir[2]);
284	greg	1.1	}
285
286
287			printdefaults() /* print default values */
288			{
289	greg	2.13	switch (skytype) {
290			case S_OVER:
291	greg	1.1	printf("-c\t\t\t\t# Cloudy sky\n");
292	greg	2.13	break;
293			case S_UNIF:
294			printf("-u\t\t\t\t# Uniform cloudy sky\n");
295			break;
296			case S_INTER:
297			if (dosun)
298			printf("+i\t\t\t\t# Intermediate sky with sun\n");
299			else
300			printf("-i\t\t\t\t# Intermediate sky without sun\n");
301			break;
302			case S_CLEAR:
303			if (dosun)
304			printf("+s\t\t\t\t# Sunny sky with sun\n");
305			else
306			printf("-s\t\t\t\t# Sunny sky without sun\n");
307			break;
308			}
309	greg	1.1	printf("-g %f\t\t\t# Ground plane reflectance\n", gprefl);
310			if (zenithbr > 0.0)
311			printf("-b %f\t\t\t# Zenith radiance (watts/ster/m2\n", zenithbr);
312			else
313			printf("-t %f\t\t\t# Atmospheric turbidity\n", turbidity);
314			printf("-a %f\t\t\t# Site latitude (degrees)\n", s_latitude*(180/PI));
315			printf("-o %f\t\t\t# Site longitude (degrees)\n", s_longitude*(180/PI));
316			printf("-m %f\t\t\t# Standard meridian (degrees)\n", s_meridian*(180/PI));
317			}
318
319
320			userror(msg) /* print usage error and quit */
321			char *msg;
322			{
323			if (msg != NULL)
324			fprintf(stderr, "%s: Use error - %s\n", progname, msg);
325			fprintf(stderr, "Usage: %s month day hour [options]\n", progname);
326	greg	2.3	fprintf(stderr, " Or: %s -ang altitude azimuth [options]\n", progname);
327	greg	1.1	fprintf(stderr, " Or: %s -defaults\n", progname);
328			exit(1);
329			}
330
331
332			double
333	greg	2.13	normsc() /* compute normalization factor (E0F2/L0) /
334	greg	1.1	{
335	greg	2.13	static double nfc[2][5] = {
336			/* clear sky approx. */
337			{2.766521, 0.547665, -0.369832, 0.009237, 0.059229},
338			/* intermediate sky approx. */
339			{3.5556, -2.7152, -1.3081, 1.0660, 0.60227},
340			};
341			register double *nf;
342	greg	1.1	double x, nsc;
343			register int i;
344			/* polynomial approximation */
345	greg	2.13	nf = nfc[skytype==S_INTER];
346			x = (altitude - PI/4.0)/(PI/4.0);
347			nsc = nf[i=4];
348			while (i--)
349	greg	1.1	nsc = nsc*x + nf[i];
350
351			return(nsc);
352	greg	2.16	}
353
354
355			cvthour(hs) /* convert hour string */
356			char *hs;
357			{
358			register char *cp = hs;
359	greg	2.17	register int i, j;
360	greg	2.16
361	greg	2.17	if (tsolar = cp == '+') cp++; / solar time? */
362			while (isdigit(*cp)) cp++;
363			if (*cp == ':')
364			hour = atoi(hs) + atoi(++cp)/60.0;
365			else {
366	greg	2.16	hour = atof(hs);
367	greg	2.17	if (*cp == '.') cp++;
368			}
369			while (isdigit(*cp)) cp++;
370			if (!*cp)
371			return;
372			if (tsolar \|\| !isalpha(*cp)) {
373			fprintf(stderr, "%s: bad time format: %s\n", progname, hs);
374			exit(1);
375			}
376			i = 0;
377			do {
378			for (j = 0; cp[j]; j++)
379			if (toupper(cp[j]) != tzone[i].zname[j])
380			break;
381			if (!cp[j] && !tzone[i].zname[j]) {
382			s_meridian = tzone[i].zmer * (PI/180);
383			return;
384			}
385			} while (tzone[i++].zname[0]);
386
387			fprintf(stderr, "%s: unknown time zone: %s\n", progname, cp);
388			fprintf(stderr, "Known time zones:\n\t%s", tzone[0].zname);
389			for (i = 1; tzone[i].zname[0]; i++)
390			fprintf(stderr, " %s", tzone[i].zname);
391			putc('\n', stderr);
392			exit(1);
393	greg	1.1	}
394
395
396			printhead(ac, av) /* print command header */
397			register int ac;
398			register char **av;
399			{
400			putchar('#');
401			while (ac--) {
402			putchar(' ');
403			fputs(*av++, stdout);
404			}
405			putchar('\n');
406			}