src/gen/gendaymtx.c

#ifndef lint
static const char RCSid[] = "$Id: gendaymtx.c,v 2.43 2025/06/06 19:11:21 greg Exp $";
#endif
/*
 *  gendaymtx.c
 *  
 *  Generate a daylight matrix based on Perez Sky Model.
 *
 *  Most of this code is borrowed (see copyright below) from Ian Ashdown's
 *  excellent re-implementation of Jean-Jacques Delaunay's gendaylit.c
 *
 *  Created by Greg Ward on 1/16/13.
 */

/*********************************************************************
 *
 *  H32_gendaylit.CPP - Perez Sky Model Calculation
 *
 *  Version:    1.00A
 *
 *  History:    09/10/01 - Created.
 *                              11/10/08 - Modified for Unix compilation.
 *                              11/10/12 - Fixed conditional __max directive.
 *                              1/11/13 - Tweaks and optimizations (G.Ward)
 *
 *  Compilers:  Microsoft Visual C/C++ Professional V10.0    
 *
 *  Author:     Ian Ashdown, P.Eng.
 *              byHeart Consultants Limited
 *              620 Ballantree Road
 *              West Vancouver, B.C.
 *              Canada V7S 1W3
 *              e-mail: [email protected]
 *
 *  References: Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R.
 *                              Stewart. 1990. ìModeling Daylight Availability and
 *                              Irradiance Components from Direct and Global
 *                              Irradiance,î Solar Energy 44(5):271-289.
 *
 *                              Perez, R., R. Seals, and J. Michalsky. 1993.
 *                              ìAll-Weather Model for Sky Luminance Distribution -
 *                              Preliminary Configuration and Validation,î Solar Energy
 *                              50(3):235-245.
 *
 *                              Perez, R., R. Seals, and J. Michalsky. 1993. "ERRATUM to
 *                              All-Weather Model for Sky Luminance Distribution -
 *                              Preliminary Configuration and Validation,î Solar Energy
 *                              51(5):423.
 *
 *  NOTE:               This program is a completely rewritten version of
 *                              gendaylit.c written by Jean-Jacques Delaunay (1994).
 *
 *  Copyright 2009-2012 byHeart Consultants Limited. All rights
 *  reserved.
 *
 *  Redistribution and use in source and binary forms, with or without
 *  modification, are permitted for personal and commercial purposes
 *  provided that redistribution of source code must retain the above
 *  copyright notice, this list of conditions and the following
 *  disclaimer:
 *
 *    THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESSED OR IMPLIED
 *    WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 *    OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 *    DISCLAIMED. IN NO EVENT SHALL byHeart Consultants Limited OR
 *    ITS EMPLOYEES BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 *    SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 *    LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 *    USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
 *    AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 *    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
 *    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 *    POSSIBILITY OF SUCH DAMAGE.
 *
 *********************************************************************/

/* Zenith is along the Z-axis */
/* X-axis points east */
/* Y-axis points north */
/* azimuth is measured as degrees or radians east of North */

/* Include files */
#define _USE_MATH_DEFINES
#include <stdlib.h>
#include <ctype.h>
#include "platform.h"
#include "rtmath.h"
#include "rtio.h"
#include "color.h"
#include "sun.h"
#include "loadEPW.h"

const double DC_SolarConstantE = 1367.0;        /* Solar constant W/m^2 */
const double DC_SolarConstantL = 127.5;         /* Solar constant klux */

double altitude;                        /* Solar altitude (radians) */
double azimuth;                         /* Solar azimuth (radians) */
double apwc;                            /* Atmospheric precipitable water content */
double dew_point = 11.0;                /* Surface dew point temperature (deg. C) */
double diff_illum;                      /* Diffuse illuminance */
double diff_irrad;                      /* Diffuse irradiance */
double dir_illum;                       /* Direct illuminance */
double dir_irrad;                       /* Direct irradiance */
int julian_date;                        /* Julian date */
double perez_param[5];                  /* Perez sky model parameters */
double sky_brightness;                  /* Sky brightness */
double sky_clearness;                   /* Sky clearness */
double solar_rad;                       /* Solar radiance */
double sun_zenith;                      /* Sun zenith angle (radians) */
int     input = 0;                              /* Input type */
int     output = 0;                             /* Output type */

extern double dmax( double, double );
extern double CalcAirMass();
extern double CalcDiffuseIllumRatio( int );
extern double CalcDiffuseIrradiance();
extern double CalcDirectIllumRatio( int );
extern double CalcDirectIrradiance();
extern double CalcEccentricity();
extern double CalcPrecipWater( double );
extern double CalcRelHorzIllum( float *parr );
extern double CalcRelLuminance( double, double );
extern double CalcSkyBrightness();
extern double CalcSkyClearness();
extern int CalcSkyParamFromIllum();
extern int GetCategoryIndex();
extern void CalcPerezParam( double, double, double, int );
extern void CalcSkyPatchLumin( float *parr );
extern void ComputeSky( float *parr );


extern double  solar_sunset(int month, int day);
extern double  solar_sunrise(int month, int day);

/* Degrees into radians */
#define DegToRad(deg)   ((deg)*(PI/180.))

/* Radiuans into degrees */
#define RadToDeg(rad)   ((rad)*(180./PI))

/* Perez sky model coefficients */

/* Reference:   Perez, R., R. Seals, and J. Michalsky, 1993. "All- */
/*                              Weather Model for Sky Luminance Distribution - */
/*                              Preliminary Configuration and Validation," Solar */
/*                              Energy 50(3):235-245, Table 1. */

static const double PerezCoeff[8][20] =
{
        /* Sky clearness (epsilon): 1.000 to 1.065 */
        {   1.3525,  -0.2576,  -0.2690,  -1.4366,   -0.7670,
            0.0007,   1.2734,  -0.1233,   2.8000,    0.6004,
            1.2375,   1.0000,   1.8734,   0.6297,    0.9738,
            0.2809,   0.0356,  -0.1246,  -0.5718,    0.9938 },
    /* Sky clearness (epsilon): 1.065 to 1.230 */
        {  -1.2219,  -0.7730,   1.4148,   1.1016,   -0.2054,
            0.0367,  -3.9128,   0.9156,   6.9750,    0.1774,
                6.4477,  -0.1239,  -1.5798,  -0.5081,   -1.7812,
                0.1080,   0.2624,   0.0672,  -0.2190,   -0.4285 },
    /* Sky clearness (epsilon): 1.230 to 1.500 */
        {  -1.1000,  -0.2515,   0.8952,   0.0156,    0.2782,
           -0.1812, - 4.5000,   1.1766,  24.7219,  -13.0812,
          -37.7000,  34.8438,  -5.0000,   1.5218,    3.9229,
           -2.6204,  -0.0156,   0.1597,   0.4199,   -0.5562 },
    /* Sky clearness (epsilon): 1.500 to 1.950 */
        {  -0.5484,  -0.6654,  -0.2672,   0.7117,   0.7234,
           -0.6219,  -5.6812,   2.6297,  33.3389, -18.3000,
          -62.2500,  52.0781,  -3.5000,   0.0016,   1.1477,
            0.1062,   0.4659,  -0.3296,  -0.0876,  -0.0329 },
    /* Sky clearness (epsilon): 1.950 to 2.800 */
        {  -0.6000,  -0.3566,  -2.5000,   2.3250,   0.2937,
            0.0496,  -5.6812,   1.8415,  21.0000,  -4.7656 ,
          -21.5906,   7.2492,  -3.5000,  -0.1554,   1.4062,
            0.3988,   0.0032,   0.0766,  -0.0656,  -0.1294 },
    /* Sky clearness (epsilon): 2.800 to 4.500 */
        {  -1.0156,  -0.3670,   1.0078,   1.4051,   0.2875,
           -0.5328,  -3.8500,   3.3750,  14.0000,  -0.9999,
           -7.1406,   7.5469,  -3.4000,  -0.1078,  -1.0750,
            1.5702,  -0.0672,   0.4016,   0.3017,  -0.4844 },
    /* Sky clearness (epsilon): 4.500 to 6.200 */
        {  -1.0000,   0.0211,   0.5025,  -0.5119,  -0.3000,
            0.1922,   0.7023,  -1.6317,  19.0000,  -5.0000,
                1.2438,  -1.9094,  -4.0000,   0.0250,   0.3844,
                0.2656,   1.0468,  -0.3788,  -2.4517,   1.4656 },
    /* Sky clearness (epsilon): 6.200 to ... */
        {  -1.0500,   0.0289,   0.4260,   0.3590,  -0.3250,
            0.1156,   0.7781,   0.0025,  31.0625, -14.5000,
          -46.1148,  55.3750,  -7.2312,   0.4050,  13.3500,
            0.6234,   1.5000,  -0.6426,   1.8564,   0.5636 }
};

/* Perez irradiance component model coefficients */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289. */

typedef struct
{
        double lower;   /* Lower bound */
        double upper;   /* Upper bound */
} CategoryBounds;

/* Perez sky clearness (epsilon) categories (Table 1) */
static const CategoryBounds SkyClearCat[8] =
{
        { 1.000, 1.065 },       /* Overcast */
        { 1.065, 1.230 },
        { 1.230, 1.500 },
        { 1.500, 1.950 },
        { 1.950, 2.800 },
        { 2.800, 4.500 },
        { 4.500, 6.200 },
        { 6.200, 12.01 }        /* Clear */
};

/* Luminous efficacy model coefficients */
typedef struct
{
        double a;
        double b;
        double c;
        double d;
} ModelCoeff;

/* Diffuse luminous efficacy model coefficients (Table 4, Eqn. 7) */
static const ModelCoeff DiffuseLumEff[8] =
{
        {  97.24, -0.46,  12.00,  -8.91 },
        { 107.22,  1.15,   0.59,  -3.95 },
        { 104.97,  2.96,  -5.53,  -8.77 },
        { 102.39,  5.59, -13.95, -13.90 },
        { 100.71,  5.94, -22.75, -23.74 },
        { 106.42,  3.83, -36.15, -28.83 },
        { 141.88,  1.90, -53.24, -14.03 },
        { 152.23,  0.35, -45.27,  -7.98 }
};

/* Direct luminous efficacy model coefficients (Table 4, Eqn. 8) */
static const ModelCoeff DirectLumEff[8] =
{
        {  57.20, -4.55, -2.98, 117.12 },
        {  98.99, -3.46, -1.21,  12.38 },
        { 109.83, -4.90, -1.71,  -8.81 },
        { 110.34, -5.84, -1.99,  -4.56 },
        { 106.36, -3.97, -1.75,  -6.16 },
        { 107.19, -1.25, -1.51, -26.73 },
        { 105.75,  0.77, -1.26, -34.44 },
        { 101.18,  1.58, -1.10,  -8.29 }
};

#ifndef NSUNPATCH
#define NSUNPATCH       4               /* max. # patches to spread sun into */
#endif

#define SUN_ANG_DEG     0.533           /* sun full-angle in degrees */

int             nsuns = NSUNPATCH;      /* number of sun patches to use */
double          fixed_sun_sa = -1;      /* fixed solid angle per sun? */

int             verbose = 0;            /* progress reports to stderr? */

int             outfmt = 'a';           /* output format */

int             rhsubdiv = 1;           /* Reinhart sky subdivisions */

COLOR           skycolor = {.96, 1.004, 1.118}; /* sky coloration */
COLOR           suncolor = {1., 1., 1.};        /* sun color */
COLOR           grefl = {.2, .2, .2};           /* ground reflectance */

int             nskypatch;              /* number of Reinhart patches */
float           *rh_palt;               /* sky patch altitudes (radians) */
float           *rh_pazi;               /* sky patch azimuths (radians) */
float           *rh_dom;                /* sky patch solid angle (sr) */

#define         vector(v,alt,azi)       (       (v)[1] = cos(alt), \
                                                (v)[0] = (v)[1]*sin(azi), \
                                                (v)[1] *= cos(azi), \
                                                (v)[2] = sin(alt) )

#define         rh_vector(v,i)          vector(v,rh_palt[i],rh_pazi[i])

#define         rh_cos(i)               tsin(rh_palt[i])

#define         solar_minute(jd,hr)     ((24*60)*((jd)-1)+(int)((hr)*60.+.5))

extern int      rh_init(void);
extern float *  resize_dmatrix(float *mtx_data, int nsteps, int npatch);
extern void     OutputSun(int id, int goodsun, FILE *fp, FILE *mfp);
extern void     AddDirect(float *parr);


static const char *
getfmtname(int fmt)
{
        switch (fmt) {
        case 'a':
                return("ascii");
        case 'f':
                return("float");
        case 'd':
                return("double");
        }
        return("unknown");
}


int
main(int argc, char *argv[])
{
        EPWheader       *epw = NULL;    /* EPW/WEA input file */
        EPWrecord       erec;           /* current EPW/WEA input record */
        float   dpthist[2];             /* previous dew point temps */
        double  dir, dif;
        int     doheader = 1;           /* output header? */
        double  rotation = 0;           /* site rotation (degrees) */
        double  elevation;              /* site elevation (meters) */
        int     leap_day = 0;           /* add leap day? */
        int     sun_hours_only = 0;     /* only output sun hours? */
        int     dir_is_horiz;           /* direct is meas. on horizontal? */
        FILE    *sunsfp = NULL;         /* output file for individual suns */
        FILE    *modsfp = NULL;         /* modifier output file */
        float   *mtx_data = NULL;       /* our matrix data */
        int     avgSky = 0;             /* compute average sky r.t. matrix? */
        int     ntsteps = 0;            /* number of time steps */
        int     tstorage = 0;           /* number of allocated time steps */
        int     nstored = 0;            /* number of time steps in matrix */
        int     last_monthly = 0;       /* month of last report */
        int     mtx_offset;
        int     i, j;
        double  timeinterval = 0;

        fixargv0(argv[0]);
                                        /* get options */
        for (i = 1; i < argc && argv[i][0] == '-'; i++)
                switch (argv[i][1]) {
                case 'g':                       /* ground reflectance */
                        grefl[0] = atof(argv[++i]);
                        grefl[1] = atof(argv[++i]);
                        grefl[2] = atof(argv[++i]);
                        break;
                case 'v':                       /* verbose progress reports */
                        verbose++;
                        break;
                case 'h':                       /* turn off header */
                        doheader = 0;
                        break;
                case 'o':                       /* output format */
                        switch (argv[i][2]) {
                        case 'f':
                        case 'd':
                        case 'a':
                                outfmt = argv[i][2];
                                break;
                        default:
                                goto userr;
                        }
                        break;
                case 'O':                       /* output type */
                        switch (argv[i][2]) {
                        case '0':
                                output = 0;
                                break;
                        case '1':
                                output = 1;
                                break;
                        default:
                                goto userr;
                        }
                        if (argv[i][3])
                                goto userr;
                        break;
                case 'm':                       /* Reinhart subdivisions */
                        rhsubdiv = atoi(argv[++i]);
                        break;
                case 'c':                       /* sky color */
                        skycolor[0] = atof(argv[++i]);
                        skycolor[1] = atof(argv[++i]);
                        skycolor[2] = atof(argv[++i]);
                        break;
                case 'D':                       /* output suns to file */
                        if (strcmp(argv[++i], "-")) {
                                sunsfp = fopen(argv[i], "w");
                                if (sunsfp == NULL) {
                                        fprintf(stderr,
                                        "%s: cannot open '%s' for output\n",
                                                        progname, argv[i]);
                                        exit(1);
                                }
                                break;          /* still may output matrix */
                        }
                        sunsfp = stdout;        /* sending to stdout, so... */
                        /* fall through */
                case 'n':                       /* no matrix output */
                        avgSky = -1;
                        rhsubdiv = 1;
                        /* fall through */
                case 'd':                       /* solar (direct) only */
                        skycolor[0] = skycolor[1] = skycolor[2] = 0;
                        grefl[0] = grefl[1] = grefl[2] = 0;
                        break;
                case 'M':                       /* send sun modifiers to file */
                        if ((modsfp = fopen(argv[++i], "w")) == NULL) {
                                fprintf(stderr, "%s: cannot open '%s' for output\n",
                                                progname, argv[i]);
                                exit(1);
                        }
                        break;
                case 's':                       /* sky only (no direct) */
                        suncolor[0] = suncolor[1] = suncolor[2] = 0;
                        break;
                case 'u':                       /* solar hours only */
                        sun_hours_only = 1;
                        break;
                case 'r':                       /* rotate distribution */
                        if (argv[i][2] && argv[i][2] != 'z')
                                goto userr;
                        rotation = atof(argv[++i]);
                        break;
                case '5':                       /* 5-phase calculation */
                        nsuns = 1;
                        fixed_sun_sa = PI/360.*atof(argv[++i]);
                        if (fixed_sun_sa <= 0) {
                                fprintf(stderr, "%s: missing solar disk size argument for '-5' option\n",
                                                progname);
                                exit(1);
                        }
                        fixed_sun_sa *= fixed_sun_sa*PI;
                        break;
                case 'A':                       /* compute average sky */
                        avgSky = 1;
                        break;
                case 'i':
                        timeinterval = atof(argv[++i]);
                        break;
                default:
                        goto userr;
                }
        if ((i < argc-1) | (i > argc))
                goto userr;
        epw = EPWopen(argv[i]);
        if (epw == NULL)
                exit(1);
        if ((modsfp != NULL) & (sunsfp == NULL))
                fprintf(stderr, "%s: warning -M output will be empty without -D\n",
                                progname);
        if (verbose) {
                if (i == argc-1)
                        fprintf(stderr, "%s: reading weather tape '%s'\n",
                                        progname, argv[i]);
                else
                        fprintf(stderr, "%s: reading weather tape from <stdin>\n",
                                        progname);
        }
                                        /* read weather tape header */
        s_latitude = epw->loc.latitude;
        s_longitude = -epw->loc.longitude;
        s_meridian = -15.*epw->loc.timezone;
        elevation = epw->loc.elevation;
        switch (epw->isWEA) {           /* translate units */
        case WEAnot:
        case WEAradnorm:
                input = 1;              /* radiometric quantities */
                dir_is_horiz = 0;       /* direct is perpendicular meas. */
                break;
        case WEAradhoriz:
                input = 1;              /* radiometric quantities */
                dir_is_horiz = 1;       /* solar measured horizontally */
                break;
        case WEAphotnorm:
                input = 2;              /* photometric quantities */
                dir_is_horiz = 0;       /* direct is perpendicular meas. */
                break;
        default:
                goto fmterr;
        }
        rh_init();                      /* initialize sky patches */
        if (verbose) {
                fprintf(stderr, "%s: location '%s, %s'\n", progname,
                                epw->loc.city, epw->loc.country);
                fprintf(stderr, "%s: (lat,long)=(%.1f,%.1f) degrees north, west\n",
                                progname, s_latitude, s_longitude);
                if (avgSky >= 0)
                        fprintf(stderr, "%s: %d sky patches\n",
                                        progname, nskypatch);
                if (sunsfp)
                        fprintf(stderr, "%s: outputting suns to %s\n",
                                        progname, sunsfp==stdout ? "stdout" : "file");
                if (rotation != 0)
                        fprintf(stderr, "%s: rotating output %.0f degrees\n",
                                        progname, rotation);
        }
                                        /* convert quantities to radians */
        s_latitude = DegToRad(s_latitude);
        s_longitude = DegToRad(s_longitude);
        s_meridian = DegToRad(s_meridian);
                                        /* initial allocation */
        mtx_data = resize_dmatrix(mtx_data, tstorage=2, nskypatch);
        dpthist[0] = -100;
                                        /* process each time step in tape */
        while ((j = EPWread(epw, &erec)) > 0) {
                const int       mo = erec.date.month+1;
                const int       da = erec.date.day;
                const double    hr = erec.date.hour;
                double          sda, sta, st;
                int             sun_in_sky;
                                        /* 3-hour dew point temp */
                if (EPWisset(&erec,dptemp)) {
                        if (dpthist[0] < -99)
                                dpthist[0] = dpthist[1] = erec.dptemp;
                        dew_point = (1./3.)*(dpthist[0] + dpthist[1] + erec.dptemp);
                        dpthist[0] = dpthist[1]; dpthist[1] = erec.dptemp;
                } else
                        dpthist[0] = -100;
                                        /* compute solar position */
                if ((mo == 2) & (da == 29)) {
                        julian_date = 60;
                        leap_day = 1;
                } else
                        julian_date = jdate(mo, da) + leap_day;
                sda = sdec(julian_date);
                sta = stadj(julian_date);
                st = hr + sta;
                
                if (timeinterval > 0) {
                        if (fabs(solar_sunrise(mo, da) - st) <= timeinterval/120)
                                st = (st + timeinterval/120 + solar_sunrise(mo, da))/2;
                        else if (fabs(solar_sunset(mo, da) - st) < timeinterval/120)
                                st = (st - timeinterval/120 + solar_sunset(mo, da))/2;
                }
                altitude = salt(sda, st);
                sun_in_sky = (altitude > -DegToRad(SUN_ANG_DEG/2.));
                if (sun_hours_only & !sun_in_sky)
                        continue;       /* skipping nighttime points */
                azimuth = sazi(sda, st) + PI - DegToRad(rotation);

                switch (epw->isWEA) {           /* translate units */
                case WEAnot:
                case WEAradnorm:
                        if (!EPWisset(&erec,dirirrad) |
                                        !EPWisset(&erec,horizdiffirrad)) {
                                fprintf(stderr, "%s: missing required irradiances at line %d\n",
                                                progname, epw->lino);
                                exit(1);
                        }
                        dir = erec.dirirrad;
                        dif = erec.horizdiffirrad;
                        break;
                case WEAradhoriz:
                        dir = erec.globhorizirrad - erec.horizdiffirrad;
                        dif = erec.horizdiffirrad;
                        break;
                case WEAphotnorm:
                        dir = erec.dirillum;
                        dif = erec.diffillum;
                        break;
                }
                mtx_offset = 3*nskypatch*nstored;
                nstored += !avgSky | !nstored;
                                        /* make space for next row */
                if (nstored > tstorage) {
                        tstorage += (tstorage>>1) + nstored + 7;
                        mtx_data = resize_dmatrix(mtx_data, tstorage, nskypatch);
                }
                ntsteps++;              /* keep count of time steps */

                if (dir+dif <= 1e-4) {  /* effectively nighttime? */
                        if (!avgSky | !mtx_offset)
                                memset(mtx_data+mtx_offset, 0,
                                                sizeof(float)*3*nskypatch);
                                        /* output black sun? */
                        if (sunsfp && sun_in_sky)
                                OutputSun(solar_minute(julian_date,hr), 0,
                                                        sunsfp, modsfp);
                        continue;
                }
                if (!sun_in_sky && dir > (input==1 ? 20. : 20.*WHTEFFICACY))
                        fprintf(stderr,
                                "%s: warning - unusually bright at %.1f on %d-%d\n",
                                        progname, hr, mo, da);
                                        /* convert measured values */
                if (dir_is_horiz && altitude > FTINY)
                        dir /= sin(altitude);
                if (input == 1) {
                        dir_irrad = dir;
                        diff_irrad = dif;
                } else /* input == 2 */ {
                        dir_illum = dir;
                        diff_illum = dif;
                }
                                        /* compute sky patch values */
                ComputeSky(mtx_data+mtx_offset);
                                        /* output sun if requested */
                if (sunsfp && sun_in_sky)
                        OutputSun(solar_minute(julian_date,hr), 1,
                                                sunsfp, modsfp);

                if (avgSky < 0)         /* no matrix? */
                        continue;

                AddDirect(mtx_data+mtx_offset);
                                        /* update cumulative sky? */
                for (i = 3*nskypatch*(avgSky&(ntsteps>1)); i--; )
                        mtx_data[i] += mtx_data[mtx_offset+i];
                                        /* monthly reporting */
                if (verbose && mo != last_monthly)
                        fprintf(stderr, "%s: stepping through month %d...\n",
                                                progname, last_monthly=mo);
                                        /* note whether leap-day was given */
        }
        if (j != EOF) {
                fprintf(stderr, "%s: error on input\n", progname);
                exit(1);
        }
        EPWclose(epw); epw = NULL;
        if (!ntsteps) {
                fprintf(stderr, "%s: no valid time steps on input\n", progname);
                exit(1);
        }
        if (avgSky < 0)                 /* no matrix output? */
                goto alldone;

        dif = 1./(double)ntsteps;       /* average sky? */
        for (i = 3*nskypatch*(avgSky&(ntsteps>1)); i--; )
                mtx_data[i] *= dif;
                                        /* write out matrix */
        if (outfmt != 'a')
                SET_FILE_BINARY(stdout);
#ifdef getc_unlocked
        flockfile(stdout);
#endif
        if (verbose)
                fprintf(stderr, "%s: writing %smatrix with %d time steps...\n",
                                progname, outfmt=='a' ? "" : "binary ", nstored);
        if (doheader) {
                newheader("RADIANCE", stdout);
                printargs(argc, argv, stdout);
                printf("LATLONG= %.8f %.8f\n", RadToDeg(s_latitude),
                                        -RadToDeg(s_longitude));
                printf("NROWS=%d\n", nskypatch);
                printf("NCOLS=%d\n", nstored);
                printf("NCOMP=3\n");
                if ((outfmt == 'f') | (outfmt == 'd'))
                        fputendian(stdout);
                fputformat((char *)getfmtname(outfmt), stdout);
                putchar('\n');
        }
                                        /* patches are rows (outer sort) */
        for (i = 0; i < nskypatch; i++) {
                mtx_offset = 3*i;
                switch (outfmt) {
                case 'a':
                        for (j = 0; j < nstored; j++) {
                                printf("%.3g %.3g %.3g\n", mtx_data[mtx_offset],
                                                mtx_data[mtx_offset+1],
                                                mtx_data[mtx_offset+2]);
                                mtx_offset += 3*nskypatch;
                        }
                        if (nstored > 1)
                                fputc('\n', stdout);
                        break;
                case 'f':
                        for (j = 0; j < nstored; j++) {
                                putbinary(mtx_data+mtx_offset, sizeof(float), 3,
                                                stdout);
                                mtx_offset += 3*nskypatch;
                        }
                        break;
                case 'd':
                        for (j = 0; j < nstored; j++) {
                                double  ment[3];
                                ment[0] = mtx_data[mtx_offset];
                                ment[1] = mtx_data[mtx_offset+1];
                                ment[2] = mtx_data[mtx_offset+2];
                                putbinary(ment, sizeof(double), 3, stdout);
                                mtx_offset += 3*nskypatch;
                        }
                        break;
                }
                if (ferror(stdout))
                        goto writerr;
        }
alldone:
        if (fflush(NULL) == EOF)
                goto writerr;
        if (verbose)
                fprintf(stderr, "%s: done.\n", progname);
        exit(0);
userr:
        fprintf(stderr, "Usage: %s [-v][-h][-A][-d|-s|-n][-u][-D file [-M modfile]][-r deg][-m N][-g r g b][-c r g b][-o{f|d}][-O{0|1}] [tape.wea]\n",
                        progname);
        exit(1);
fmterr:
        fprintf(stderr, "%s: weather tape format error in header\n", progname);
        exit(1);
writerr:
        fprintf(stderr, "%s: write error on output\n", progname);
        exit(1);
}


/* Return maximum of two doubles */
double dmax( double a, double b )
{ return (a > b) ? a : b; }

/* Compute sky patch radiance values (modified by GW) */
void
ComputeSky(float *parr)
{
        int index;                      /* Category index */
        double norm_diff_illum;         /* Normalized diffuse illuimnance */
        int i;

        /* Calculate atmospheric precipitable water content */
        apwc = CalcPrecipWater(dew_point);

        /* Calculate sun zenith angle (don't let it dip below horizon) */
        /* Also limit minimum angle to keep circumsolar off zenith */
        if (altitude <= 0.0)
                sun_zenith = DegToRad(90.0);
        else if (altitude >= DegToRad(87.0))
                sun_zenith = DegToRad(3.0);
        else
                sun_zenith = DegToRad(90.0) - altitude;

        /* Compute the inputs for the calculation of the sky distribution */
        
        if (input == 0)                                 /* XXX never used */
        {
                /* Calculate irradiance */
                diff_irrad = CalcDiffuseIrradiance();
                dir_irrad = CalcDirectIrradiance();
                
                /* Calculate illuminance */
                index = GetCategoryIndex();
                diff_illum = diff_irrad * CalcDiffuseIllumRatio(index);
                dir_illum = dir_irrad * CalcDirectIllumRatio(index);
        }
        else if (input == 1)
        {
                sky_brightness = CalcSkyBrightness();
                sky_clearness =  CalcSkyClearness();

                /* Limit sky clearness */
                if (sky_clearness > 11.9)
                        sky_clearness = 11.9;
                else if (sky_clearness < 1.0)
                        sky_clearness = 1.0;

                /* Limit sky brightness */
                if (sky_brightness < 0.01)
                        sky_brightness = 0.01;
                else if (sky_brightness > 0.6)
                        sky_brightness = 0.6;

                /* Calculate illuminance */
                index = GetCategoryIndex();
                diff_illum = diff_irrad * CalcDiffuseIllumRatio(index);
                dir_illum = dir_irrad * CalcDirectIllumRatio(index);
        }
        else if (input == 2)
        {
                /* Calculate sky brightness and clearness from illuminance values */
                index = CalcSkyParamFromIllum();
        }

        if (output == 1) {                      /* hack for solar radiance */
                diff_illum = diff_irrad * WHTEFFICACY;
                dir_illum = dir_irrad * WHTEFFICACY;
        }
        /* Compute ground radiance (include solar contribution if any) */
        parr[0] = diff_illum;
        if (altitude > 0)
                parr[0] += dir_illum * sin(altitude);
        parr[2] = parr[1] = parr[0] *= (1./PI/WHTEFFICACY);
        multcolor(parr, grefl);

        if (bright(skycolor) <= 1e-4) {                 /* 0 sky component? */
                memset(parr+3, 0, sizeof(float)*3*(nskypatch-1));
                return;
        }
        /* Calculate Perez sky model parameters */
        CalcPerezParam(sun_zenith, sky_clearness, sky_brightness, index);

        /* Calculate sky patch luminance values */
        CalcSkyPatchLumin(parr);

        /* Calculate relative horizontal illuminance */
        norm_diff_illum = CalcRelHorzIllum(parr);

        /* Check for zero sky -- make uniform in that case */
        if (norm_diff_illum <= FTINY) {
                for (i = 1; i < nskypatch; i++)
                        setcolor(parr+3*i, 1., 1., 1.);
                norm_diff_illum = PI;
        }
        /* Normalization coefficient */
        norm_diff_illum = diff_illum / norm_diff_illum;

        /* Apply to sky patches to get absolute radiance values */
        for (i = 1; i < nskypatch; i++) {
                scalecolor(parr+3*i, norm_diff_illum*(1./WHTEFFICACY));
                multcolor(parr+3*i, skycolor);
        }
}


double
solar_sunset(int month, int day)
{
        float W;
        W = -1 * (tan(s_latitude) * tan(sdec(jdate(month, day))));
        return(12 + (M_PI / 2 - atan2(W, sqrt(1 - W * W))) * 180 / (M_PI * 15));
}


double
solar_sunrise(int month, int day)
{
        float W;
        W = -1 * (tan(s_latitude) * tan(sdec(jdate(month, day))));
        return(12 - (M_PI / 2 - atan2(W, sqrt(1 - W * W))) * 180 / (M_PI * 15));
}


/* Add in solar direct to nearest sky patches (GW) */
void
AddDirect(float *parr)
{
        FVECT   svec;
        double  near_dprod[NSUNPATCH];
        int     near_patch[NSUNPATCH];
        double  wta[NSUNPATCH], wtot;
        int     i, j, p;

        if (dir_illum <= 1e-4 || bright(suncolor) <= 1e-4)
                return;
                                        /* identify nsuns closest patches */
        if (nsuns > NSUNPATCH)
                nsuns = NSUNPATCH;
        else if (nsuns <= 0)
                nsuns = 1;
        for (i = nsuns; i--; )
                near_dprod[i] = -1.;
        vector(svec, altitude, azimuth);
        for (p = 1; p < nskypatch; p++) {
                FVECT   pvec;
                double  dprod;
                rh_vector(pvec, p);
                dprod = DOT(pvec, svec);
                for (i = 0; i < nsuns; i++)
                        if (dprod > near_dprod[i]) {
                                for (j = nsuns; --j > i; ) {
                                        near_dprod[j] = near_dprod[j-1];
                                        near_patch[j] = near_patch[j-1];
                                }
                                near_dprod[i] = dprod;
                                near_patch[i] = p;
                                break;
                        }
        }
        wtot = 0;                       /* weight by proximity */
        for (i = nsuns; i--; )
                wtot += wta[i] = 1./(1.002 - near_dprod[i]);
                                        /* add to nearest patch radiances */
        for (i = nsuns; i--; ) {
                float   *pdest = parr + 3*near_patch[i];
                float   val_add = wta[i] * dir_illum / (WHTEFFICACY * wtot);

                val_add /= (fixed_sun_sa > 0)   ? fixed_sun_sa 
                                                : rh_dom[near_patch[i]] ;
                *pdest++ += val_add*suncolor[0];
                *pdest++ += val_add*suncolor[1];
                *pdest++ += val_add*suncolor[2];
        }
}

/* Output a sun to indicated file if appropriate for this time step */
void
OutputSun(int id, int goodsun, FILE *fp, FILE *mfp)
{
        double  srad;
        FVECT   sv;

        srad = DegToRad(SUN_ANG_DEG/2.);
        srad = goodsun ? dir_illum/(WHTEFFICACY * PI*srad*srad) : 0;
        vector(sv, altitude, azimuth);
        fprintf(fp, "\nvoid light solar%d\n0\n0\n", id);
        fprintf(fp, "3 %.3e %.3e %.3e\n", srad*suncolor[0],
                        srad*suncolor[1], srad*suncolor[2]);
        fprintf(fp, "\nsolar%d source sun%d\n0\n0\n", id, id);
        fprintf(fp, "4 %.6f %.6f %.6f %.4f\n", sv[0], sv[1], sv[2], SUN_ANG_DEG);
        
        if (mfp != NULL)                /* saving modifier IDs? */
                fprintf(mfp, "solar%d\n", id);
}

/* Initialize Reinhart sky patch positions (GW) */
int
rh_init(void)
{
#define NROW    7
        static const int        tnaz[NROW] = {30, 30, 24, 24, 18, 12, 6};
        const double            alpha = (PI/2.)/(NROW*rhsubdiv + .5);
        int                     p, i, j;
                                        /* allocate patch angle arrays */
        nskypatch = 0;
        for (p = 0; p < NROW; p++)
                nskypatch += tnaz[p];
        nskypatch *= rhsubdiv*rhsubdiv;
        nskypatch += 2;
        rh_palt = (float *)malloc(sizeof(float)*nskypatch);
        rh_pazi = (float *)malloc(sizeof(float)*nskypatch);
        rh_dom = (float *)malloc(sizeof(float)*nskypatch);
        if ((rh_palt == NULL) | (rh_pazi == NULL) | (rh_dom == NULL)) {
                fprintf(stderr, "%s: out of memory in rh_init()\n", progname);
                exit(1);
        }
        rh_palt[0] = -PI/2.;            /* ground & zenith patches */
        rh_pazi[0] = 0.;
        rh_dom[0] = 2.*PI;
        rh_palt[nskypatch-1] = PI/2.;
        rh_pazi[nskypatch-1] = 0.;
        rh_dom[nskypatch-1] = 2.*PI*(1. - cos(alpha*.5));
        p = 1;                          /* "normal" patches */
        for (i = 0; i < NROW*rhsubdiv; i++) {
                const float     ralt = alpha*(i + .5);
                const int       ninrow = tnaz[i/rhsubdiv]*rhsubdiv;
                const float     dom = 2.*PI*(sin(alpha*(i+1)) - sin(alpha*i)) /
                                                (double)ninrow;
                for (j = 0; j < ninrow; j++) {
                        rh_palt[p] = ralt;
                        rh_pazi[p] = 2.*PI * j / (double)ninrow;
                        rh_dom[p++] = dom;
                }
        }
        return nskypatch;
#undef NROW
}

/* Resize daylight matrix (GW) */
float *
resize_dmatrix(float *mtx_data, int nsteps, int npatch)
{
        if (mtx_data == NULL)
                mtx_data = (float *)malloc(sizeof(float)*3*nsteps*npatch);
        else
                mtx_data = (float *)realloc(mtx_data,
                                        sizeof(float)*3*nsteps*npatch);
        if (mtx_data == NULL) {
                fprintf(stderr, "%s: out of memory in resize_dmatrix(%d,%d)\n",
                                progname, nsteps, npatch);
                exit(1);
        }
        return(mtx_data);
}

/* Determine category index */
int GetCategoryIndex()
{
        int index;      /* Loop index */

        for (index = 0; index < 8; index++)
                if ((sky_clearness >= SkyClearCat[index].lower) &&
                                (sky_clearness < SkyClearCat[index].upper))
                        break;

        return index;
}

/* Calculate diffuse illuminance to diffuse irradiance ratio */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289, Eqn. 7. */

double CalcDiffuseIllumRatio( int index )
{
        ModelCoeff const *pnle; /* Category coefficient pointer */
        
        /* Get category coefficient pointer */
        pnle = &(DiffuseLumEff[index]);

        return pnle->a + pnle->b * apwc + pnle->c * cos(sun_zenith) +
                        pnle->d * log(sky_brightness);
}

/* Calculate direct illuminance to direct irradiance ratio */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289, Eqn. 8. */

double CalcDirectIllumRatio( int index )
{
        ModelCoeff const *pnle; /* Category coefficient pointer */

        /* Get category coefficient pointer */
        pnle = &(DirectLumEff[index]);

        /* Calculate direct illuminance from direct irradiance */
        
        return dmax((pnle->a + pnle->b * apwc + pnle->c * exp(5.73 *
                        sun_zenith - 5.0) + pnle->d * sky_brightness),
                        0.0);
}

/* Calculate sky brightness */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289, Eqn. 2. */

double CalcSkyBrightness()
{
        return diff_irrad * CalcAirMass() / (DC_SolarConstantE *
                        CalcEccentricity());
}

/* Calculate sky clearness */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289, Eqn. 1. */

double CalcSkyClearness()
{
        double sz_cubed;        /* Sun zenith angle cubed */

        /* Calculate sun zenith angle cubed */
        sz_cubed = sun_zenith*sun_zenith*sun_zenith;

        return ((diff_irrad + dir_irrad) / diff_irrad + 1.041 *
                        sz_cubed) / (1.0 + 1.041 * sz_cubed);
}

/* Calculate diffuse horizontal irradiance from Perez sky brightness */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289, Eqn. 2 */
/*                              (inverse). */

double CalcDiffuseIrradiance()
{
        return sky_brightness * DC_SolarConstantE * CalcEccentricity() /
                        CalcAirMass();
}

/* Calculate direct normal irradiance from Perez sky clearness */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289, Eqn. 1 */
/*                              (inverse). */

double CalcDirectIrradiance()
{
        return CalcDiffuseIrradiance() * ((sky_clearness - 1.0) * (1 + 1.041
                        * sun_zenith*sun_zenith*sun_zenith));
}

/* Calculate sky brightness and clearness from illuminance values */
int CalcSkyParamFromIllum()
{
        double test1 = 0.1;
        double test2 = 0.1;
        int     counter = 0;
        int index = 0;                  /* Category index */

        /* Convert illuminance to irradiance */
        diff_irrad = diff_illum * DC_SolarConstantE /
                        (DC_SolarConstantL * 1000.0);
        dir_irrad = dir_illum * DC_SolarConstantE /
                        (DC_SolarConstantL * 1000.0);

        /* Calculate sky brightness and clearness */
        sky_brightness = CalcSkyBrightness();
        sky_clearness =  CalcSkyClearness(); 

        /* Limit sky clearness */
        if (sky_clearness > 12.0)
                sky_clearness = 12.0;

        /* Limit sky brightness */
        if (sky_brightness < 0.01)
                        sky_brightness = 0.01; 

        if (sky_clearness < 1.0000)
        {
                sky_clearness = 1.0000;
        }

        if (sky_brightness > 0.6)
        {
                sky_brightness = 0.6;
        }

        while (((fabs(diff_irrad - test1) > 10.0) ||
                        (fabs(dir_irrad - test2) > 10.0)) && !(counter == 5))
        {
                test1 = diff_irrad;
                test2 = dir_irrad;      
                counter++;
        
                /* Convert illuminance to irradiance */
                index = GetCategoryIndex();
                diff_irrad = diff_illum / CalcDiffuseIllumRatio(index);
                dir_irrad = CalcDirectIllumRatio(index);
                if (dir_irrad > 0.1)
                        dir_irrad = dir_illum / dir_irrad;
        
                /* Calculate sky brightness and clearness */
                sky_brightness = CalcSkyBrightness();
                sky_clearness =  CalcSkyClearness();

                /* Limit sky clearness */
                if (sky_clearness > 12.0)
                        sky_clearness = 12.0;
        
                /* Limit sky brightness */
                if (sky_brightness < 0.01)
                        sky_brightness = 0.01; 

                if (sky_clearness < 1.0000)
                {
                        sky_clearness = 1.0000;
                }

                if (sky_brightness > 0.6)
                {
                        sky_brightness = 0.6;
                }
        }

        return GetCategoryIndex();
}               

/* Calculate relative luminance */

/* Reference:   Perez, R., R. Seals, and J. Michalsky. 1993. */
/*                              ìAll-Weather Model for Sky Luminance Distribution - */
/*                              Preliminary Configuration and Validation,î Solar Energy */
/*                              50(3):235-245, Eqn. 1. */

double CalcRelLuminance( double gamma, double zeta )
{
        return (1.0 + perez_param[0] * exp(perez_param[1] / cos(zeta))) *
                    (1.0 + perez_param[2] * exp(perez_param[3] * gamma) +
                        perez_param[4] * cos(gamma) * cos(gamma));
}

/* Calculate Perez sky model parameters */

/* Reference:   Perez, R., R. Seals, and J. Michalsky. 1993. */
/*                              ìAll-Weather Model for Sky Luminance Distribution - */
/*                              Preliminary Configuration and Validation,î Solar Energy */
/*                              50(3):235-245, Eqns. 6 - 8. */

void CalcPerezParam( double sz, double epsilon, double delta,
                int index )
{
        double x[5][4];         /* Coefficents a, b, c, d, e */
        int i, j;                       /* Loop indices */

        /* Limit sky brightness */
        if (epsilon > 1.065 && epsilon < 2.8)
        {
                if (delta < 0.2)
                        delta = 0.2;
        }

        /* Get Perez coefficients */
        for (i = 0; i < 5; i++)
                for (j = 0; j < 4; j++)
                        x[i][j] = PerezCoeff[index][4 * i + j];

        if (index != 0)
        {
                /* Calculate parameter a, b, c, d and e (Eqn. 6) */
                for (i = 0; i < 5; i++)
                        perez_param[i] = x[i][0] + x[i][1] * sz + delta * (x[i][2] +
                                        x[i][3] * sz);
        }
        else
        {
                /* Parameters a, b and e (Eqn. 6) */
                perez_param[0] = x[0][0] + x[0][1] * sz + delta * (x[0][2] +
                                x[0][3] * sz);
                perez_param[1] = x[1][0] + x[1][1] * sz + delta * (x[1][2] +
                                x[1][3] * sz);
                perez_param[4] = x[4][0] + x[4][1] * sz + delta * (x[4][2] +
                                x[4][3] * sz);

                /* Parameter c (Eqn. 7) */
                perez_param[2] = exp(pow(delta * (x[2][0] + x[2][1] * sz),
                                x[2][2])) - x[2][3];

                /* Parameter d (Eqn. 8) */
                perez_param[3] = -exp(delta * (x[3][0] + x[3][1] * sz)) + 
                                x[3][2] + delta * x[3][3];
        }
}

/* Calculate relative horizontal illuminance (modified by GW) */

/* Reference:   Perez, R., R. Seals, and J. Michalsky. 1993. */
/*                              ìAll-Weather Model for Sky Luminance Distribution - */
/*                              Preliminary Configuration and Validation,î Solar Energy */
/*                              50(3):235-245, Eqn. 3. */

double CalcRelHorzIllum( float *parr )
{
        int i;
        double rh_illum = 0.0;  /* Relative horizontal illuminance */

        for (i = 1; i < nskypatch; i++)
                rh_illum += parr[3*i+1] * rh_cos(i) * rh_dom[i];

        return rh_illum;
}

/* Calculate earth orbit eccentricity correction factor */

/* Reference:   Sen, Z. 2008. Solar Energy Fundamental and Modeling  */
/*                              Techniques. Springer, p. 72. */

double CalcEccentricity()
{
        double day_angle;       /* Day angle (radians) */
        double E0;                      /* Eccentricity */

        /* Calculate day angle */
        day_angle  = (julian_date - 1.0) * (2.0 * PI / 365.0);

        /* Calculate eccentricity */
        E0 = 1.00011 + 0.034221 * cos(day_angle) + 0.00128 * sin(day_angle)
                        + 0.000719 * cos(2.0 * day_angle) + 0.000077 * sin(2.0 *
                        day_angle);

        return E0;
}

/* Calculate atmospheric precipitable water content */

/* Reference:   Perez, R., P. Ineichen, R. Seals, J. Michalsky, and R. */
/*                              Stewart. 1990. ìModeling Daylight Availability and */
/*                              Irradiance Components from Direct and Global */
/*                              Irradiance,î Solar Energy 44(5):271-289, Eqn. 3. */

/* Note:        The default surface dew point temperature is 11 deg. C */
/*                      (52 deg. F). Typical values are: */

/*                      Celsius         Fahrenheit              Human Perception */
/*                      > 24            > 75                    Extremely uncomfortable */
/*                      21 - 24         70 - 74                 Very humid */
/*                      18 - 21         65 - 69                 Somewhat uncomfortable */
/*                      16 - 18         60 - 64                 OK for most people */
/*                      13 - 16         55 - 59                 Comfortable */
/*                      10 - 12         50 - 54                 Very comfortable */
/*                      < 10            < 49                    A bit dry for some */

double CalcPrecipWater( double dpt )
{ return exp(0.07 * dpt - 0.075); }

/* Calculate relative air mass */

/* Reference:   Kasten, F. 1966. "A New Table and Approximation Formula */
/*                              for the Relative Optical Air Mass," Arch. Meteorol. */
/*                              Geophys. Bioklimataol. Ser. B14, pp. 206-233. */

/* Note:                More sophisticated relative air mass models are */
/*                              available, but they differ significantly only for */
/*                              sun zenith angles greater than 80 degrees. */

double CalcAirMass()
{
        return (1.0 / (cos(sun_zenith) + 0.15 * pow(93.885 -
                        RadToDeg(sun_zenith), -1.253)));
}

/* Calculate Perez All-Weather sky patch luminances (modified by GW) */

/* NOTE: The sky patches centers are determined in accordance with the */
/*       BRE-IDMP sky luminance measurement procedures. (See for example */
/*       Mardaljevic, J. 2001. "The BRE-IDMP Dataset: A New Benchmark */
/*       for the Validation of Illuminance Prediction Techniques," */
/*       Lighting Research & Technology 33(2):117-136.) */

void CalcSkyPatchLumin( float *parr )
{
        int i;
        double aas;                             /* Sun-sky point azimuthal angle */
        double sspa;                    /* Sun-sky point angle */
        double zsa;                             /* Zenithal sun angle */

        for (i = 1; i < nskypatch; i++)
        {
                /* Calculate sun-sky point azimuthal angle */
                aas = fabs(rh_pazi[i] - azimuth);

                /* Calculate zenithal sun angle */
                zsa = PI * 0.5 - rh_palt[i];

                /* Calculate sun-sky point angle (Equation 8-20) */
                sspa = acos(cos(sun_zenith) * cos(zsa) + sin(sun_zenith) *
                                sin(zsa) * cos(aas));

                /* Calculate patch luminance */
                parr[3*i] = CalcRelLuminance(sspa, zsa);
                if (parr[3*i] < 0) parr[3*i] = 0;
                parr[3*i+2] = parr[3*i+1] = parr[3*i];
        }
}
Revision:	2.44
Committed:	Sat Jun 7 05:09:45 2025 UTC (18 hours, 35 minutes ago) by greg
Content type:	text/plain
Branch:	MAIN
CVS Tags:	HEAD
Changes since 2.43:	+1 -2 lines
Log Message:	refactor: Put some declarations into "paths.h" and included in "platform.h"