src/gen/gendaylit.c

/*      Copyright (c) 1994,2006 *Fraunhofer Institut for Solar Energy Systems
 *                              Heidenhofstr. 2, D-79110 Freiburg, Germany
 *                              *Agence de l'Environnement et de la Maitrise de l'Energie
 *                              Centre de Valbonne, 500 route des Lucioles, 06565 Sophia Antipolis Cedex, France
 *                              *BOUYGUES 
 *                              1 Avenue Eugene Freyssinet, Saint-Quentin-Yvelines, France
*  print colored output if activated in command line (-C). Based on model from A. Diakite, TU-Berlin. Implemented by J. Wienold, August 26 2018
*/

#define  _USE_MATH_DEFINES
#include  <stdio.h>
#include  <string.h>
#include  <math.h>
#include  <stdlib.h>

#include  "color.h"
#include  "sun.h"
#include  "paths.h"

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

double  normsc();

/*static        char *rcsid="$Header: /cvs/radiance/ray/src/gen/gendaylit.c,v 2.19 2019/12/04 18:11:57 greg Exp $";*/

float coeff_perez[] = {
        1.3525,-0.2576,-0.2690,-1.4366,-0.7670,0.0007,1.2734,-0.1233,2.8000,0.6004,1.2375,1.000,1.8734,0.6297,
        0.9738,0.2809,0.0356,-0.1246,-0.5718,0.9938,-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,-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,-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,-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,-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,-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,-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};


float defangle_theta[] = {
        84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84, 84,
        84, 84, 84, 84, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72, 72,
        72, 72, 72, 72, 72, 72, 72, 72, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60, 60,
        60, 60, 60, 60, 60, 60, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48, 48,
        48, 48, 48, 48, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 36, 24, 24, 24, 24,
        24, 24, 24, 24, 24, 24, 24, 24, 12, 12, 12, 12, 12, 12, 0};

float defangle_phi[] = {
        0, 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144, 156, 168, 180, 192, 204, 216, 228, 240, 252, 264,
        276, 288, 300, 312, 324, 336, 348, 0, 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132, 144, 156, 168, 180,
        192, 204, 216, 228, 240, 252, 264, 276, 288, 300, 312, 324, 336, 348, 0, 15, 30, 45, 60, 75, 90, 105,
        120, 135, 150, 165, 180, 195, 210, 225, 240, 255, 270, 285, 300, 315, 330, 345, 0, 15, 30, 45, 60, 75,
        90, 105, 120, 135, 150, 165, 180, 195, 210, 225, 240, 255, 270, 285, 300, 315, 330, 345, 0, 20, 40, 60,
        80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 0, 30, 60, 90, 120, 150, 180, 210,
        240, 270, 300, 330, 0, 60, 120, 180, 240, 300, 0};
/* default values for Berlin */
float   locus[] = {
-4.843e9,2.5568e6,0.24282e3,0.23258,-4.843e9,2.5568e6,0.24282e3,0.23258,-1.2848,1.7519,-0.093786};


/* Perez sky parametrization: epsilon and delta calculations from the direct and diffuse irradiances */
double sky_brightness();
double sky_clearness();

/* calculation of the direct and diffuse components from the Perez parametrization */
double  diffuse_irradiance_from_sky_brightness();
double  direct_irradiance_from_sky_clearness();

/* Perez global horizontal, diffuse horizontal and direct normal luminous efficacy models : */
/* input w(cm)=2cm, solar zenith angle(degrees); output efficacy(lm/W) */

double  glob_h_effi_PEREZ();
double  glob_h_diffuse_effi_PEREZ();
double  direct_n_effi_PEREZ();

/*likelihood check of the epsilon, delta, direct and diffuse components*/
void    check_parametrization();
void    check_irradiances();
void    check_illuminances();
void    illu_to_irra_index();
void    print_error_sky();

double  calc_rel_lum_perez(double dzeta,double gamma,double Z,double epsilon,double Delta,float coeff_perez[]);
void    coeff_lum_perez(double Z, double epsilon, double Delta, float coeff_perez[]);
double  radians(double degres);
double  degres(double radians);
void    theta_phi_to_dzeta_gamma(double theta,double phi,double *dzeta,double *gamma, double Z);
double  integ_lv(float *lv,float *theta);

void printdefaults();
void check_sun_position();
void computesky();
void printhead(int ac, char** av);
void usage_error(char* msg);
void printsky();

FILE * frlibopen(char* fname);

/* astronomy and geometry*/
double  get_eccentricity();
double  air_mass();

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

const double    AU = 149597890E3;
const double    solar_constant_e = 1367;    /* solar constant W/m^2 */
const double    solar_constant_l = 127500;   /* solar constant lux */

const double    half_sun_angle = 0.2665;
const double    half_direct_angle = 2.85;

const double    skyclearinf = 1.0;          /* limitations for the variation of the Perez parameters */
const double    skyclearsup = 12.01;
const double    skybriginf = 0.01;
const double    skybrigsup = 0.6;


/* required values */
int  year = 0;                                  /* year (optional) */
int     month, day;                             /* date */
double  hour;                                   /* time */
int     tsolar;                                 /* 0=standard, 1=solar */
double  altitude, azimuth;                      /* or solar angles */


/* definition of the sky conditions through the Perez parametrization */
double  skyclearness = 0; 
double  skybrightness = 0;
double  solarradiance;
double  diffuseilluminance, directilluminance, diffuseirradiance, directirradiance, globalirradiance;
double  sunzenith, daynumber, atm_preci_water=2;

/*double  sunaltitude_border = 0;*/
double  diffnormalization = 0;
double  dirnormalization = 0;
double  *c_perez;

int     output=0;       /* define the unit of the output (sky luminance or radiance): */
                        /* visible watt=0, solar watt=1, lumen=2 */
int     input=0;        /* define the input for the calulation */
int     color_output=0;
int     suppress_warnings=0;

        /* default values */
int     cloudy = 0;                             /* 1=standard, 2=uniform */
int     dosun = 1;
double  zenithbr = -1.0;
double  betaturbidity = 0.1;
double  gprefl = 0.2;
int     S_INTER=0;


        /* computed values */
double  sundir[3];
double  groundbr = 0;
double  F2;
double  solarbr = 0.0;
int     u_solar = 0;                            /* -1=irradiance, 1=radiance */
float   timeinterval = 0;

char    *progname;
char    errmsg[128];

double  st;


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

        progname = argv[0];
        if (argc == 2 && !strcmp(argv[1], "-defaults")) {
                printdefaults();
                return 0;
        }
        if (argc < 4)
                usage_error("arg count");
        if (!strcmp(argv[1], "-ang")) {
                altitude = atof(argv[2]) * (M_PI/180);
                azimuth = atof(argv[3]) * (M_PI/180);
                month = 0;
        } else {
                month = atoi(argv[1]);
                if (month < 1 || month > 12)
                        usage_error("bad month");
                day = atoi(argv[2]);
                if (day < 1 || day > 31)
                        usage_error("bad day");
                hour = atof(argv[3]);
                if (hour < 0 || hour >= 24)
                        usage_error("bad hour");
                tsolar = argv[3][0] == '+';
        }
        for (i = 4; i < argc; i++)
                if (argv[i][0] == '-' || argv[i][0] == '+')
                        switch (argv[i][1]) {
                        case 's':
                                cloudy = 0;
                                dosun = argv[i][0] == '+';
                                break;
                        case 'y':
                                year = atoi(argv[++i]);
                                break;
                        case 'R':
                                u_solar = argv[i][1] == 'R' ? -1 : 1;
                                solarbr = atof(argv[++i]);
                                break;
                        case 'c':
                                cloudy = argv[i][0] == '+' ? 2 : 1;
                                dosun = 0;
                                break;
                        case 'C':
                                if (argv[i][2] == 'I' && argv[i][3] == 'E' ) {
                                locus[0] = -4.607e9;
                                locus[1] = 2.9678e6;
                                locus[2] = 0.09911e3;
                                locus[3] = 0.244063;
                                locus[4] = -2.0064e9;
                                locus[5] = 1.9018e6;
                                locus[6] = 0.24748e3;
                                locus[7] = 0.23704;
                                locus[8] = -3.0;
                                locus[9] = 2.87;
                                locus[10] = -0.275;
                                 }else{ color_output = 1;
                                 }
                                break;
                        case 'l':
                                locus[0] = atof(argv[++i]);
                                locus[1] = atof(argv[++i]);
                                locus[2] = atof(argv[++i]);
                                locus[3] = atof(argv[++i]);
                                locus[4] = locus[0];
                                locus[5] = locus[1];
                                locus[6] = locus[2];
                                locus[7] = locus[3];
                                locus[8] = atof(argv[++i]);
                                locus[9] = atof(argv[++i]);
                                locus[10] = atof(argv[++i]);
                                break;

                        case 't':
                                betaturbidity = atof(argv[++i]);
                                break;
                        case 'w':
                                suppress_warnings = 1;
                                break;                  
                        case 'b':
                                zenithbr = atof(argv[++i]);
                                break;
                        case 'g':
                                gprefl = atof(argv[++i]);
                                break;
                        case 'a':
                                s_latitude = atof(argv[++i]) * (M_PI/180);
                                break;
                        case 'o':
                                s_longitude = atof(argv[++i]) * (M_PI/180);
                                break;
                        case 'm':
                                s_meridian = atof(argv[++i]) * (M_PI/180);
                                break;
                        
                        case 'O':
                                output = atof(argv[++i]);       /*define the unit of the output of the program: 
                                                                sky and sun luminance/radiance
                                                                (0==W visible, 1==W solar radiation, 2==lm) */
                                break;
                                
                        case 'P':
                                input = 0;                              /* Perez parameters: epsilon, delta */
                                skyclearness = atof(argv[++i]);
                                skybrightness = atof(argv[++i]);
                                break;

                        case 'W':                                       /* direct normal Irradiance [W/m^2] */
                                input = 1;                              /* diffuse horizontal Irrad. [W/m^2] */
                                directirradiance = atof(argv[++i]);
                                diffuseirradiance = atof(argv[++i]);
                                break;
                                
                        case 'L':                                       /* direct normal Illuminance [Lux] */
                                input = 2;                              /* diffuse horizontal Ill. [Lux] */
                                directilluminance = atof(argv[++i]);
                                diffuseilluminance = atof(argv[++i]);
                                break;
                        
                        case 'G':                                       /* direct horizontal Irradiance [W/m^2] */
                                input = 3;                              /* diffuse horizontal Irrad. [W/m^2] */
                                directirradiance = atof(argv[++i]);
                                diffuseirradiance = atof(argv[++i]);
                                break;
                        
                        case 'E':                                       /* Erbs model based on the */
                                input = 4;                              /* global-horizontal irradiance [W/m^2] */
                                globalirradiance = atof(argv[++i]);
                                break;
                        
                        case 'i':
                                timeinterval = atof(argv[++i]);
                                break;
                        
                        
                        default:
                                sprintf(errmsg, "unknown option: %s", argv[i]);
                                usage_error(errmsg);
                        }
                else
                        usage_error("bad option");

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


        /* dynamic memory allocation for the pointers */
        if ( (c_perez = calloc(5, sizeof(double))) == NULL )
        { fprintf(stderr,"Out of memory error in function main"); return 1; }

        
        printhead(argc, argv);
        computesky();
        printsky();
        return 0;

}


void computesky()
{

        int     j;
        
        float   *lv_mod;  /* 145 luminance values */
        float   *theta_o, *phi_o;
        double  dzeta, gamma;
        double  normfactor;
        double  erbs_s0, erbs_kt;


        /* compute solar direction */
                
        if (month) {                    /* from date and time */
                double  sd;

                st = hour;
                if (year) {                     /* Michalsky algorithm? */
                        double  mjd = mjdate(year, month, day, hour);
                        if (tsolar)
                                sd = msdec(mjd, NULL);
                        else
                                sd = msdec(mjd, &st);
                } else {
                        int  jd = jdate(month, day);    /* Julian date */
                        sd = sdec(jd);                  /* solar declination */
                        if (!tsolar)                    /* get solar time? */
                                st = hour + stadj(jd);
                }
                                                        
                if(timeinterval) {
                        
                        if(timeinterval<0) {
                        fprintf(stderr, "time interval negative\n");
                        exit(1);
                        }
                                                                        
                        if(fabs(solar_sunrise(month,day)-st)<=timeinterval/120) {                       
                         st= (st+timeinterval/120+solar_sunrise(month,day))/2;
                         if(suppress_warnings==0)
                         { fprintf(stderr, "Solar position corrected at time step %d %d %.3f\n",month,day,hour); }
                        }
                
                        if(fabs(solar_sunset(month,day)-st)<timeinterval/120) {
                         st= (st-timeinterval/120+solar_sunset(month,day))/2;
                         if(suppress_warnings==0)
                         { fprintf(stderr, "Solar position corrected at time step %d %d %.3f\n",month,day,hour); }
                        }
                        
                        if((st<solar_sunrise(month,day)-timeinterval/120) || (st>solar_sunset(month,day)+timeinterval/120)) {
                          if(suppress_warnings==0)
                          { fprintf(stderr, "Warning: sun position too low, printing error sky at %d %d %.3f\n",month,day,hour); }
                         altitude = salt(sd, st);
                         azimuth = sazi(sd, st);
                         print_error_sky();
                         exit(0);
                        } 
                }
                else
                
                if(st<solar_sunrise(month,day) || st>solar_sunset(month,day)) {
                        if(suppress_warnings==0)
                        { fprintf(stderr, "Warning: sun altitude below zero at time step %i %i %.2f, printing error sky\n",month,day,hour); }
                        altitude = salt(sd, st);
                        azimuth = sazi(sd, st);
                        print_error_sky();
                        exit(0);
                }
                
                altitude = salt(sd, st);
                azimuth = sazi(sd, st);
                
                daynumber = (double)jdate(month, day);
                
        }
        
        
        if (!cloudy && altitude > 87.*M_PI/180.) {
                
                if (suppress_warnings==0) { 
                    fprintf(stderr,
                    "%s: warning - sun too close to zenith, reducing altitude to 87 degrees\n",
                    progname);
                }
                altitude = 87.*M_PI/180.;
        }
        
        
        sundir[0] = -sin(azimuth)*cos(altitude);
        sundir[1] = -cos(azimuth)*cos(altitude);
        sundir[2] = sin(altitude);
        
                
        /* calculation for the new functions */
        sunzenith = 90 - altitude*180/M_PI;
                        

        /* compute the inputs for the calculation of the light distribution over the sky*/
        if (input==0)           /* P */
                {
                check_parametrization();
                diffuseirradiance = diffuse_irradiance_from_sky_brightness(); /*diffuse horizontal irradiance*/
                directirradiance = direct_irradiance_from_sky_clearness();
                check_irradiances();
                
                if (output==0 || output==2)
                        {
                        diffuseilluminance = diffuseirradiance*glob_h_diffuse_effi_PEREZ();/*diffuse horizontal illuminance*/
                        directilluminance = directirradiance*direct_n_effi_PEREZ();
                        check_illuminances();
                        }
                }
        

        else if (input==1)      /* W */
                {
                check_irradiances();
                skybrightness = sky_brightness();
                skyclearness =  sky_clearness();
                
                check_parametrization();
                                                        
                if (output==0 || output==2)
                        {
                        diffuseilluminance = diffuseirradiance*glob_h_diffuse_effi_PEREZ();/*diffuse horizontal illuminance*/
                        directilluminance = directirradiance*direct_n_effi_PEREZ();
                        check_illuminances();
                        }

                }
                        
        
        else if (input==2)      /* L */
                {               
                check_illuminances();
                illu_to_irra_index();
                check_parametrization();
                }
                

        else if (input==3)      /* G */
                {
                        if (altitude<=0)
                        {
                                if (suppress_warnings==0)
                                     fprintf(stderr, "Warning: sun altitude < 0, proceed with irradiance values of zero\n");
                                directirradiance = 0;
                                diffuseirradiance = 0;
                        } else {
                        
                                directirradiance=directirradiance/sin(altitude);
                        }
                                
                check_irradiances();
                skybrightness = sky_brightness();
                skyclearness =  sky_clearness();
                check_parametrization();

                if (output==0 || output==2)
                        {
                        diffuseilluminance = diffuseirradiance*glob_h_diffuse_effi_PEREZ();/*diffuse horizontal illuminance*/
                        directilluminance = directirradiance*direct_n_effi_PEREZ();
                        check_illuminances();
                        }

                }


        else if (input==4)      /* E */         /* Implementation of the Erbs model. W.Sprenger (04/13) */
                {
                        
                        if (altitude<=0)
                        {
                                if (suppress_warnings==0 && globalirradiance > 50)
                                        fprintf(stderr, "Warning: global irradiance higher than 50 W/m^2 while the sun altitude is lower than zero\n");
                                globalirradiance = 0; diffuseirradiance = 0; directirradiance = 0;
                        
                        } else {
                        
                        erbs_s0 = solar_constant_e*get_eccentricity()*sin(altitude);
                        
                        if (globalirradiance>erbs_s0)
                        {
                                if (suppress_warnings==0)
                                        fprintf(stderr, "Warning: global irradiance is higher than the time-dependent solar constant s0\n");
                                globalirradiance=erbs_s0*0.999;                 
                        }
                        
                        erbs_kt=globalirradiance/erbs_s0;
                        
                        if (erbs_kt<=0.22)      diffuseirradiance=globalirradiance*(1-0.09*erbs_kt);
                        else if (erbs_kt<=0.8)  diffuseirradiance=globalirradiance*(0.9511-0.1604*erbs_kt+4.388*pow(erbs_kt,2)-16.638*pow(erbs_kt,3)+12.336*pow(erbs_kt,4));
                        else if (erbs_kt<1)     diffuseirradiance=globalirradiance*(0.165);
                        
                        directirradiance=globalirradiance-diffuseirradiance;
                        
                        printf("# erbs_s0, erbs_kt, irr_dir_h, irr_diff: %.3f %.3f %.3f %.3f\n", erbs_s0, erbs_kt, directirradiance, diffuseirradiance);
                        printf("# WARNING: the -E option is only recommended for a rough estimation!\n");
                        
                        directirradiance=directirradiance/sin(altitude);
                                                                                                                        
                        }
                        
                check_irradiances();
                skybrightness = sky_brightness();
                skyclearness =  sky_clearness();
                check_parametrization();

                if (output==0 || output==2)
                        {
                        diffuseilluminance = diffuseirradiance*glob_h_diffuse_effi_PEREZ();/*diffuse horizontal illuminance*/
                        directilluminance = directirradiance*direct_n_effi_PEREZ();
                        check_illuminances();
                        }

                }
                
                
        else    { fprintf(stderr,"error at the input arguments"); exit(1); }


        /* normalization factor for the relative sky luminance distribution, diffuse part*/
        
        if ( (lv_mod = malloc(145*sizeof(float))) == NULL)
        {
                fprintf(stderr,"Out of memory in function main");
                exit(1);
        }

        /* read the angles */
        theta_o = defangle_theta;
        phi_o = defangle_phi;
        

        /* parameters for the perez model */
        coeff_lum_perez(radians(sunzenith), skyclearness, skybrightness, coeff_perez);

        
        /*calculation of the modelled luminance */
        for (j=0;j<145;j++)
        {
                theta_phi_to_dzeta_gamma(radians(*(theta_o+j)),radians(*(phi_o+j)),&dzeta,&gamma,radians(sunzenith));
                                
                *(lv_mod+j) = calc_rel_lum_perez(dzeta,gamma,radians(sunzenith),skyclearness,skybrightness,coeff_perez);
                
                /* fprintf(stderr,"theta, phi, lv_mod %f\t %f\t %f\n", *(theta_o+j),*(phi_o+j),*(lv_mod+j)); */
        }
        
        /* integration of luminance for the normalization factor, diffuse part of the sky*/
        
        diffnormalization = integ_lv(lv_mod, theta_o);
        

        /*normalization coefficient in lumen or in watt*/
        if (output==0)
                {
                diffnormalization = diffuseilluminance/diffnormalization/WHTEFFICACY;
                }
        else if (output==1)
                {
                diffnormalization = diffuseirradiance/diffnormalization;
                }
        else if (output==2)
                {
                diffnormalization = diffuseilluminance/diffnormalization;
                }

        else    {fprintf(stderr,"Wrong output specification.\n"); exit(1);}


        /* calculation for the solar source */  
        if (output==0) 
                solarradiance = directilluminance/(2*M_PI*(1-cos(half_sun_angle*M_PI/180)))/WHTEFFICACY;
                
        else if (output==1)
                solarradiance = directirradiance/(2*M_PI*(1-cos(half_sun_angle*M_PI/180)));
        
        else
                solarradiance = directilluminance/(2*M_PI*(1-cos(half_sun_angle*M_PI/180)));
        

        /* Compute the ground radiance */
        zenithbr=calc_rel_lum_perez(0.0,radians(sunzenith),radians(sunzenith),skyclearness,skybrightness,coeff_perez);
        zenithbr*=diffnormalization;
        
        if (skyclearness==1)
        normfactor = 0.777778;
                
        if (skyclearness>=6)
        {               
        F2 = 0.274*(0.91 + 10.0*exp(-3.0*(M_PI/2.0-altitude)) + 0.45*sundir[2]*sundir[2]);
        normfactor = normsc()/F2/M_PI;
        }

        if ( (skyclearness>1) && (skyclearness<6) )
        {
        S_INTER=1;
        F2 = (2.739 + .9891*sin(.3119+2.6*altitude)) * exp(-(M_PI/2.0-altitude)*(.4441+1.48*altitude));
        normfactor = normsc()/F2/M_PI;
        }

        groundbr = zenithbr*normfactor;

        if (dosun&&(skyclearness>1)) 
        groundbr += 6.8e-5/M_PI*solarradiance*sundir[2];                

        groundbr *= gprefl;


        if(*(c_perez+1)>0)
        {
          if(suppress_warnings==0)
                {  fprintf(stderr, "Warning: positive Perez parameter B (= %lf), printing error sky\n",*(c_perez+1));}  
          print_error_sky();
          exit(0);
        }


return;
}


double solar_sunset(int month,int day)
{
     float W;
     extern double s_latitude;
     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;
     extern double s_latitude;
     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));
}


void printsky()
{       
        
        printf("# Local solar time: %.2f\n", st);
        printf("# Solar altitude and azimuth: %.1f %.1f\n", altitude*180/M_PI, azimuth*180/M_PI);


        if (dosun&&(skyclearness>1)) 
        {               
                printf("\nvoid light solar\n");
                printf("0\n0\n");
                printf("3 %.3e %.3e %.3e\n", solarradiance, solarradiance, solarradiance);
                printf("\nsolar source sun\n");
                printf("0\n0\n");
                printf("4 %f %f %f %f\n", sundir[0], sundir[1], sundir[2], 2*half_sun_angle);
        } else if (dosun) {
                printf("\nvoid light solar\n");
                printf("0\n0\n");
                printf("3 0.0 0.0 0.0\n");
                printf("\nsolar source sun\n");
                printf("0\n0\n");
                printf("4 %f %f %f %f\n", sundir[0], sundir[1], sundir[2], 2*half_sun_angle);
        }
/* print colored output if activated in command line (-C). Based on model from A. Diakite, TU-Berlin. Implemented by J. Wienold, August 26 2018 */      
        if  (color_output==1 && skyclearness < 4.5 && skyclearness >1.065 )  
        {
        fprintf(stderr, "       warning: sky clearness(epsilon)= %f \n",skyclearness);
        fprintf(stderr, "       warning: intermediate sky!! \n");
        fprintf(stderr, "       warning: color model for intermediate sky pending  \n");
        fprintf(stderr, "       warning: no color output ! \n");
        color_output=0;
        }
        if (color_output==1)
        {
        printf("\nvoid colorfunc skyfunc\n");
        printf("4 skybright_r skybright_g skybright_b perezlum_c.cal\n");
        printf("0\n");
        printf("22 %.3e %.3e %lf %lf %lf %lf %lf %f %f %f %f %f %f %f %f %f %f %f %f %f %f %f\n", diffnormalization, groundbr,
                *(c_perez+0),*(c_perez+1),*(c_perez+2),*(c_perez+3),*(c_perez+4), 
                sundir[0], sundir[1], sundir[2],skyclearness,locus[0],locus[1],locus[2],locus[3],locus[4],locus[5],locus[6],locus[7],locus[8],locus[9],locus[10]);
        }else{
        printf("\nvoid brightfunc skyfunc\n");
        printf("2 skybright perezlum.cal\n");
        printf("0\n");
        printf("10 %.3e %.3e %lf %lf %lf %lf %lf %f %f %f \n", diffnormalization, groundbr,
                *(c_perez+0),*(c_perez+1),*(c_perez+2),*(c_perez+3),*(c_perez+4),
                sundir[0], sundir[1], sundir[2]);
         }
        
}


void print_error_sky()
{


        sundir[0] = -sin(azimuth)*cos(altitude);
        sundir[1] = -cos(azimuth)*cos(altitude);
        sundir[2] = sin(altitude);

        printf("# Local solar time: %.2f\n", st);
        printf("# Solar altitude and azimuth: %.1f %.1f\n", altitude*180/M_PI, azimuth*180/M_PI);

        printf("\nvoid brightfunc skyfunc\n");
        printf("2 skybright perezlum.cal\n");
        printf("0\n");
        printf("10 0.00 0.00  0.000 0.000 0.000 0.000 0.000  %f %f %f \n", sundir[0], sundir[1], sundir[2]);
}
        

void printdefaults()                    /* print default values */
{
        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/m^2\n", zenithbr);
        else
                printf("-t %f\t\t\t# Atmospheric betaturbidity\n", betaturbidity);
        printf("-a %f\t\t\t# Site latitude (degrees)\n", s_latitude*(180/M_PI));
        printf("-o %f\t\t\t# Site longitude (degrees)\n", s_longitude*(180/M_PI));
        printf("-m %f\t\t\t# Standard meridian (degrees)\n", s_meridian*(180/M_PI));
}


void usage_error(char* msg)                     /* print usage error and quit */
{
        if (msg != NULL)
                fprintf(stderr, "%s: Use error - %s\n\n", progname, msg);
        fprintf(stderr, "Usage: %s      month day hour [-y year]        [...]\n", progname);
        fprintf(stderr, "   or: %s -ang altitude azimuth                [...]\n", progname);
        fprintf(stderr, "               followed by:      -P          epsilon delta [options]\n");
        fprintf(stderr, "                        or:      [-W|-L|-G]  direct_value diffuse_value [options]\n");
        fprintf(stderr, "                        or:      -E          global_irradiance [options]\n\n");
        fprintf(stderr, "    Description:\n");
        fprintf(stderr, "       -P epsilon delta  (these are the Perez parameters) \n");
        fprintf(stderr, "       -W direct-normal-irradiance diffuse-horizontal-irradiance (W/m^2)\n");
        fprintf(stderr, "       -L direct-normal-illuminance diffuse-horizontal-illuminance (lux)\n");
        fprintf(stderr, "       -G direct-horizontal-irradiance diffuse-horizontal-irradiance (W/m^2)\n");
        fprintf(stderr, "       -E global-horizontal-irradiance (W/m^2)\n\n");
        fprintf(stderr, "       Output specification with option:\n");
        fprintf(stderr, "       -O [0|1|2]  (0=output in W/m^2/sr visible, 1=output in W/m^2/sr solar, 2=output in candela/m^2), default is 0 \n");
        fprintf(stderr, "       gendaylit version 2.5 (2018/04/18)  \n\n");
        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[S_INTER];
        x = (altitude - M_PI/4.0)/(M_PI/4.0);
        nsc = nf[i=4];
        while (i--)
                nsc = nsc*x + nf[i];

        return(nsc);
}


void printhead(int ac, char** av)               /* print command header */
{
        putchar('#');
        while (ac--) {
                putchar(' ');
                fputs(*av++, stdout);
        }
        putchar('\n');
}


/* Perez models */

/* Perez global horizontal luminous efficacy model */
double glob_h_effi_PEREZ()
{

        double  value;
        double  category_bounds[10], a[10], b[10], c[10], d[10];
        int     category_total_number, category_number, i;
        
        check_parametrization();
        
        
/*if ((skyclearness<skyclearinf || skyclearness>skyclearsup || skybrightness<skybriginf || skybrightness>skybrigsup) && suppress_warnings==0)
     fprintf(stderr, "Warning: skyclearness or skybrightness out of range in function glob_h_effi_PEREZ \n"); */
     
     
        /* initialize category bounds (clearness index bounds) */

        category_total_number = 8;

        category_bounds[1] = 1;
        category_bounds[2] = 1.065;
        category_bounds[3] = 1.230;
        category_bounds[4] = 1.500;
        category_bounds[5] = 1.950;
        category_bounds[6] = 2.800;
        category_bounds[7] = 4.500;
        category_bounds[8] = 6.200;
        category_bounds[9] = 12.01;


        /* initialize model coefficients */
        a[1] = 96.63;
        a[2] = 107.54;
        a[3] = 98.73;
        a[4] = 92.72;
        a[5] = 86.73;
        a[6] = 88.34;
        a[7] = 78.63;
        a[8] = 99.65;

        b[1] = -0.47;
        b[2] = 0.79;
        b[3] = 0.70;
        b[4] = 0.56;
        b[5] = 0.98;
        b[6] = 1.39;
        b[7] = 1.47;
        b[8] = 1.86;

        c[1] = 11.50;
        c[2] = 1.79;
        c[3] = 4.40;
        c[4] = 8.36;
        c[5] = 7.10;
        c[6] = 6.06;
        c[7] = 4.93;
        c[8] = -4.46;

        d[1] = -9.16;
        d[2] = -1.19;
        d[3] = -6.95;
        d[4] = -8.31;
        d[5] = -10.94;
        d[6] = -7.60;
        d[7] = -11.37;
        d[8] = -3.15;


        for (i=1; i<=category_total_number; i++)
        {
                if ( (skyclearness >= category_bounds[i]) && (skyclearness < category_bounds[i+1]) )
                        category_number = i;
        }

        value = a[category_number] + b[category_number]*atm_preci_water  + 
            c[category_number]*cos(sunzenith*M_PI/180) +  d[category_number]*log(skybrightness);

        return(value);
}


/* global horizontal diffuse efficacy model, according to PEREZ */
double glob_h_diffuse_effi_PEREZ()
{
        double  value;
        double  category_bounds[10], a[10], b[10], c[10], d[10];
        int     category_total_number, category_number, i;

        check_parametrization();
        
        
/*if ((skyclearness<skyclearinf || skyclearness>skyclearsup || skybrightness<skybriginf || skybrightness>skybrigsup) && suppress_warnings==0)
 fprintf(stderr, "Warning: skyclearness or skybrightness out of range in function glob_h_diffuse_PEREZ \n"); */
     
/* initialize category bounds (clearness index bounds) */

        category_total_number = 8;

//XXX:  category_bounds > 0.1
        category_bounds[1] = 1;
        category_bounds[2] = 1.065;
        category_bounds[3] = 1.230;
        category_bounds[4] = 1.500;
        category_bounds[5] = 1.950;
        category_bounds[6] = 2.800;
        category_bounds[7] = 4.500;
        category_bounds[8] = 6.200;
        category_bounds[9] = 12.01;


        /* initialize model coefficients */
        a[1] = 97.24;
        a[2] = 107.22;
        a[3] = 104.97;
        a[4] = 102.39;
        a[5] = 100.71;
        a[6] = 106.42;
        a[7] = 141.88;
        a[8] = 152.23;

        b[1] = -0.46;
        b[2] = 1.15;
        b[3] = 2.96;
        b[4] = 5.59;
        b[5] = 5.94;
        b[6] = 3.83;
        b[7] = 1.90;
        b[8] = 0.35;

        c[1] = 12.00;
        c[2] = 0.59;
        c[3] = -5.53;
        c[4] = -13.95;
        c[5] = -22.75;
        c[6] = -36.15;
        c[7] = -53.24;
        c[8] = -45.27;

        d[1] = -8.91;
        d[2] = -3.95;
        d[3] = -8.77;
        d[4] = -13.90;
        d[5] = -23.74;
        d[6] = -28.83;
        d[7] = -14.03;
        d[8] = -7.98;


        category_number = -1;
        for (i=1; i<=category_total_number; i++)
        {
                if ( (skyclearness >= category_bounds[i]) && (skyclearness < category_bounds[i+1]) )
                        category_number = i;
        }

        if (category_number == -1) {
                if (suppress_warnings==0)
                    fprintf(stderr, "Warning: sky clearness (= %.3f) too high, printing error sky\n", skyclearness);
                print_error_sky();
                exit(0);
        }
                

        value = a[category_number] + b[category_number]*atm_preci_water  + c[category_number]*cos(sunzenith*M_PI/180) + 
            d[category_number]*log(skybrightness);

        return(value);

}


/* direct normal efficacy model, according to PEREZ */

double direct_n_effi_PEREZ()

{
double  value;
double  category_bounds[10], a[10], b[10], c[10], d[10];
int     category_total_number, category_number, i;


/*if ((skyclearness<skyclearinf || skyclearness>skyclearsup || skybrightness<skybriginf || skybrightness>skybrigsup) && suppress_warnings==0)
   fprintf(stderr, "Warning: skyclearness or skybrightness out of range in function direct_n_effi_PEREZ \n");*/


/* initialize category bounds (clearness index bounds) */

category_total_number = 8;

category_bounds[1] = 1;
category_bounds[2] = 1.065;
category_bounds[3] = 1.230;
category_bounds[4] = 1.500;
category_bounds[5] = 1.950;
category_bounds[6] = 2.800;
category_bounds[7] = 4.500;
category_bounds[8] = 6.200;
category_bounds[9] = 12.1;


/* initialize model coefficients */
a[1] = 57.20;
a[2] = 98.99;
a[3] = 109.83;
a[4] = 110.34;
a[5] = 106.36;
a[6] = 107.19;
a[7] = 105.75;
a[8] = 101.18;

b[1] = -4.55;
b[2] = -3.46;
b[3] = -4.90;
b[4] = -5.84;
b[5] = -3.97;
b[6] = -1.25;
b[7] = 0.77;
b[8] = 1.58;

c[1] = -2.98;
c[2] = -1.21;
c[3] = -1.71;
c[4] = -1.99;
c[5] = -1.75;
c[6] = -1.51;
c[7] = -1.26;
c[8] = -1.10;

d[1] = 117.12;
d[2] = 12.38;
d[3] = -8.81;
d[4] = -4.56;
d[5] = -6.16;
d[6] = -26.73;
d[7] = -34.44;
d[8] = -8.29;


for (i=1; i<=category_total_number; i++)
{
if ( (skyclearness >= category_bounds[i]) && (skyclearness < category_bounds[i+1]) )
category_number = i;
}

value = a[category_number] + b[category_number]*atm_preci_water  + c[category_number]*exp(5.73*sunzenith*M_PI/180 - 5) +  d[category_number]*skybrightness;

if (value < 0) value = 0;

return(value);
}


/*check the range of epsilon and delta indexes of the perez parametrization*/
void check_parametrization()
{

if (skyclearness<skyclearinf || skyclearness>skyclearsup || skybrightness<skybriginf || skybrightness>skybrigsup)
                {

/*  limit sky clearness or sky brightness, 2009 11 13 by J. Wienold */
                
                if (skyclearness<skyclearinf){
                        /* if (suppress_warnings==0)
                            fprintf(stderr,"Range warning: sky clearness too low (%lf)\n", skyclearness); */
                        skyclearness=skyclearinf;
                }
                if (skyclearness>skyclearsup){
                        /* if (suppress_warnings==0)
                            fprintf(stderr,"Range warning: sky clearness too high (%lf)\n", skyclearness); */
                        skyclearness=skyclearsup-0.001;
                }
                if (skybrightness<skybriginf){
                        /* if (suppress_warnings==0)
                            fprintf(stderr,"Range warning: sky brightness too low (%lf)\n", skybrightness); */
                        skybrightness=skybriginf;
                }
                if (skybrightness>skybrigsup){
                        /* if (suppress_warnings==0)
                            fprintf(stderr,"Range warning: sky brightness too high (%lf)\n", skybrightness); */
                        skybrightness=skybrigsup;
                }

        return; }
        else return;
}


/* validity of the direct and diffuse components */
void    check_illuminances()
{
        if (directilluminance < 0) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: direct illuminance < 0. Using 0.0\n"); }
                directilluminance = 0.0;
        }
        if (diffuseilluminance < 0) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: diffuse illuminance < 0. Using 0.0\n"); }
                diffuseilluminance = 0.0;
        }
        
        if (directilluminance+diffuseilluminance==0 && altitude > 0) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: zero illuminance at sun altitude > 0, printing error sky\n"); }
                print_error_sky();
                exit(0);
        }
        
        if (directilluminance > solar_constant_l) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: direct illuminance exceeds solar constant\n"); }
                print_error_sky();
                exit(0);
        }
}


void    check_irradiances()
{
        if (directirradiance < 0) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: direct irradiance < 0. Using 0.0\n"); }
                directirradiance = 0.0;
        }
        if (diffuseirradiance < 0) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: diffuse irradiance < 0. Using 0.0\n"); }
                diffuseirradiance = 0.0;
        }
        
        if (directirradiance+diffuseirradiance==0 && altitude > 0) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: zero irradiance at sun altitude > 0, printing error sky\n"); }
                print_error_sky();
                exit(0);
        }
        
        if (directirradiance > solar_constant_e) {
                if(suppress_warnings==0)
                { fprintf(stderr,"Warning: direct irradiance exceeds solar constant\n"); }
                print_error_sky();
                exit(0);
        }
}
        

/* Perez sky's brightness */
double sky_brightness()
{
double value;

value = diffuseirradiance * air_mass() / ( solar_constant_e*get_eccentricity());

return(value);
}


/* Perez sky's clearness */
double sky_clearness()
{
        double value;

        value = ( (diffuseirradiance + directirradiance)/(diffuseirradiance) + 1.041*sunzenith*M_PI/180*sunzenith*M_PI/180*sunzenith*M_PI/180 ) / (1 + 1.041*sunzenith*M_PI/180*sunzenith*M_PI/180*sunzenith*M_PI/180) ;

        return(value);
}


/* diffus horizontal irradiance from Perez sky's brightness */
double diffuse_irradiance_from_sky_brightness()
{
        double value;

        value = skybrightness / air_mass() * ( solar_constant_e*get_eccentricity());

        return(value);
}


/* direct normal irradiance from Perez sky's clearness */
double direct_irradiance_from_sky_clearness()
{
        double value;

        value = diffuse_irradiance_from_sky_brightness();
        value = value * ( (skyclearness-1) * (1+1.041*sunzenith*M_PI/180*sunzenith*M_PI/180*sunzenith*M_PI/180) );

        return(value);
}


void illu_to_irra_index()
{
double  test1=0.1, test2=0.1, d_eff;
int     counter=0;      

diffuseirradiance = diffuseilluminance*solar_constant_e/(solar_constant_l);
directirradiance = directilluminance*solar_constant_e/(solar_constant_l);
skyclearness =  sky_clearness(); 
skybrightness = sky_brightness();
check_parametrization();


while ( ((fabs(diffuseirradiance-test1)>10) || (fabs(directirradiance-test2)>10)
                || (!(skyclearness<skyclearinf || skyclearness>skyclearsup)) 
                || (!(skybrightness<skybriginf || skybrightness>skybrigsup)) )
                 && !(counter==9) )
        {
        
        test1=diffuseirradiance;
        test2=directirradiance; 
        counter++;
        
        diffuseirradiance = diffuseilluminance/glob_h_diffuse_effi_PEREZ();
        d_eff = direct_n_effi_PEREZ();
        
        
        if (d_eff < 0.1)
                directirradiance = 0;
        else    
                directirradiance = directilluminance/d_eff;
        
        skybrightness = sky_brightness();
        skyclearness =  sky_clearness();
        check_parametrization();
                
        }


return;
}               

static int get_numlin(float epsilon)
{
        if (epsilon < 1.065)
                return 0;
        else if (epsilon < 1.230) 
                return 1;
        else if (epsilon < 1.500)
                return 2;
        else if (epsilon < 1.950)
                return 3;
        else if (epsilon < 2.800)
                return 4;
        else if (epsilon < 4.500)
                return 5;
        else if (epsilon < 6.200)
                return 6;
        return 7;
}

/* sky luminance perez model */
double calc_rel_lum_perez(double dzeta,double gamma,double Z,double epsilon,double Delta,float coeff_perez[])
{
                        
        float x[5][4];
        int i,j,num_lin;
        double c_perez[5];

        if ( (epsilon <  skyclearinf) || (epsilon >= skyclearsup) )
        {
                fprintf(stderr,"Error: epsilon out of range in function calc_rel_lum_perez!\n");
                exit(1);
        }

        /* correction de modele de Perez solar energy ...*/
        if ( (epsilon > 1.065) && (epsilon < 2.8) )
        {
                if ( Delta < 0.2 ) Delta = 0.2;
        }
        
        
        num_lin = get_numlin(epsilon);
        
        for (i=0;i<5;i++)
                for (j=0;j<4;j++)
                {
                        x[i][j] = *(coeff_perez + 20*num_lin + 4*i +j);
                        /* fprintf(stderr,"x %d %d vaut %f\n",i,j,x[i][j]); */
                }


        if (num_lin)
        {
                for (i=0;i<5;i++)
                        c_perez[i] = x[i][0] + x[i][1]*Z + Delta * (x[i][2] + x[i][3]*Z);
        }
        else
        {
                c_perez[0] = x[0][0] + x[0][1]*Z + Delta * (x[0][2] + x[0][3]*Z);
                c_perez[1] = x[1][0] + x[1][1]*Z + Delta * (x[1][2] + x[1][3]*Z);
                c_perez[4] = x[4][0] + x[4][1]*Z + Delta * (x[4][2] + x[4][3]*Z);
                c_perez[2] = exp( pow(Delta*(x[2][0]+x[2][1]*Z),x[2][2])) - x[2][3];
                c_perez[3] = -exp( Delta*(x[3][0]+x[3][1]*Z) )+x[3][2]+Delta*x[3][3];
        }


        return (1 + c_perez[0]*exp(c_perez[1]/cos(dzeta)) ) *
            (1 + c_perez[2]*exp(c_perez[3]*gamma) +
            c_perez[4]*cos(gamma)*cos(gamma) );
}


/* coefficients for the sky luminance perez model */
void coeff_lum_perez(double Z, double epsilon, double Delta, float coeff_perez[])
{
        float x[5][4];
        int i,j,num_lin;

        if ( (epsilon <  skyclearinf) || (epsilon >= skyclearsup) )
        {
                fprintf(stderr,"Error: epsilon out of range in function coeff_lum_perez!\n");
                exit(1);
        }

        /* correction du modele de Perez solar energy ...*/
        if ( (epsilon > 1.065) && (epsilon < 2.8) )
        {
                if ( Delta < 0.2 ) Delta = 0.2;
        }
        
        
        num_lin = get_numlin(epsilon);

        /*fprintf(stderr,"numlin %d\n", num_lin);*/

        for (i=0;i<5;i++)
                for (j=0;j<4;j++)
                {
                        x[i][j] = *(coeff_perez + 20*num_lin + 4*i +j);
                        /* printf("x %d %d vaut %f\n",i,j,x[i][j]); */
                }


        if (num_lin)
        {
                for (i=0;i<5;i++)
                        *(c_perez+i) = x[i][0] + x[i][1]*Z + Delta * (x[i][2] + x[i][3]*Z);

        }
        else
        {
                *(c_perez+0) = x[0][0] + x[0][1]*Z + Delta * (x[0][2] + x[0][3]*Z);
                *(c_perez+1) = x[1][0] + x[1][1]*Z + Delta * (x[1][2] + x[1][3]*Z);
                *(c_perez+4) = x[4][0] + x[4][1]*Z + Delta * (x[4][2] + x[4][3]*Z);
                *(c_perez+2) = exp( pow(Delta*(x[2][0]+x[2][1]*Z),x[2][2])) - x[2][3];
                *(c_perez+3) = -exp( Delta*(x[3][0]+x[3][1]*Z) )+x[3][2]+Delta*x[3][3];


        }


        return;
}


/* degrees into radians */
double radians(double degres)
{
        return degres*(M_PI/180.);
}


/* radian into degrees */
double degres(double radians)
{
        return radians*(180./M_PI);
}


/* calculation of the angles dzeta and gamma */
void theta_phi_to_dzeta_gamma(double theta,double phi,double *dzeta,double *gamma, double Z)
{
        *dzeta = theta; /* dzeta = phi */
        if ( (cos(Z)*cos(theta)+sin(Z)*sin(theta)*cos(phi)) > 1 && (cos(Z)*cos(theta)+sin(Z)*sin(theta)*cos(phi) < 1.1 ) )
                *gamma = 0;
        else if ( (cos(Z)*cos(theta)+sin(Z)*sin(theta)*cos(phi)) > 1.1 )
        {
                printf("error in calculation of gamma (angle between point and sun");
                exit(1);
        }
        else
                *gamma = acos(cos(Z)*cos(theta)+sin(Z)*sin(theta)*cos(phi));
}


double integ_lv(float *lv,float *theta)
{
        int i;
        double buffer=0.0;
        
        for (i=0;i<145;i++)
        {
                buffer += (*(lv+i))*cos(radians(*(theta+i)));
        }
                        
        return buffer*(2.*M_PI/145.);
}


/* enter day number(double), return E0 = square(R0/R):  eccentricity correction factor  */

double get_eccentricity()
{
        double day_angle;
        double E0;

        day_angle  = 2*M_PI*(daynumber - 1)/365;
        E0         = 1.00011+0.034221*cos(day_angle)+0.00128*sin(day_angle)+
            0.000719*cos(2*day_angle)+0.000077*sin(2*day_angle);

        return (E0);
}


/* enter sunzenith angle (degrees) return relative air mass (double) */
double  air_mass()
{
double  m;
if (sunzenith>90)
        {
        if(suppress_warnings==0)
        { fprintf(stderr, "Warning: air mass has reached the maximal value\n"); }
        sunzenith=90;
        }
m = 1/( cos(sunzenith*M_PI/180)+0.15*exp( log(93.885-sunzenith)*(-1.253) ) );
return(m);
}


Revision:	2.20
Committed:	Wed Nov 18 17:18:41 2020 UTC (4 years, 11 months ago) by greg
Content type:	text/plain
Branch:	MAIN
Changes since 2.19:	+4 -4 lines
Log Message:	fix(gendaylit): correction to sky integration factor for solid angle