/*============================================================================
* Local Void function ssha
*
* Sunset hour angle, degrees
* Iqbal, M. 1983. An Introduction to Solar Radiation.
* Academic Press, NY., page 16
*----------------------------------------------------------------------------*/
private static void ssha(PosData pdat, TrigData tdat)
{
float cssha; /* cosine of the sunset hour angle */
float cdcl; /* ( cd * cl ) */
localtrig(pdat, tdat);
cdcl = tdat.cd * tdat.cl;
if (fabs(cdcl) >= 0.001f) {
cssha = -tdat.sl * tdat.sd / cdcl;
/* This keeps the cosine from blowing on roundoff */
if (cssha < -1.0f)
pdat.ssha = 180.0f;
else if (cssha > 1.0f)
pdat.ssha = 0.0f;
else
pdat.ssha = degrad * acos(cssha);
} else if (((pdat.declin >= 0.0f) && (pdat.latitude > 0.0f)) ||
((pdat.declin < 0.0f) && (pdat.latitude < 0.0f)))
pdat.ssha = 180.0f;
else
pdat.ssha = 0.0f;
}
/*============================================================================
* Local Void function sbcf
*
* Shadowband correction factor
* Drummond, A. J. 1956. A contribution to absolute pyrheliometry.
* Q. J. R. Meteorol. Soc. 82, pp. 481-493
*----------------------------------------------------------------------------*/
private static void sbcf(PosData pdat, TrigData tdat)
{
float p, t1, t2; /* used to compute sbcf */
localtrig(pdat, tdat);
p = 0.6366198f * pdat.sbwid / pdat.sbrad * pow(tdat.cd, 3);
t1 = tdat.sl * tdat.sd * pdat.ssha * raddeg;
t2 = tdat.cl * tdat.cd * sin(pdat.ssha * raddeg);
pdat.sbcf = pdat.sbsky + 1.0f / (1.0f - p * (t1 + t2));
}
/*============================================================================
* Local Void function sazm
*
* Solar azimuth angle
* Iqbal, M. 1983. An Introduction to Solar Radiation.
* Academic Press, NY., page 15
*----------------------------------------------------------------------------*/
private static void sazm(PosData pdat, TrigData tdat)
{
float ca; /* cosine of the solar azimuth angle */
float ce; /* cosine of the solar elevation */
float cecl; /* ( ce * cl ) */
float se; /* sine of the solar elevation */
localtrig(pdat, tdat);
ce = cos(raddeg * pdat.elevetr);
se = sin(raddeg * pdat.elevetr);
pdat.azim = 180.0f;
cecl = ce * tdat.cl;
if (fabs(cecl) >= 0.001) {
ca = (se * tdat.sl - tdat.sd) / cecl;
if (ca > 1.0f)
ca = 1.0f;
else if (ca < -1.0f)
ca = -1.0f;
pdat.azim = 180.0f - acos(ca) * degrad;
if (pdat.hrang > 0.0f)
pdat.azim = 360.0f - pdat.azim;
}
}
/*============================================================================
* Local Void function localtrig
*
* Does trig on internal variable used by several functions
*----------------------------------------------------------------------------*/
private static void localtrig(PosData pdat, TrigData tdat)
{
/* define masks to prevent calculation of uninitialized variables */
const int SD_MASK = (L_ZENETR | L_SSHA | S_SBCF | S_SOLAZM);
const int SL_MASK = (L_ZENETR | L_SSHA | S_SBCF | S_SOLAZM);
const int CL_MASK = (L_ZENETR | L_SSHA | S_SBCF | S_SOLAZM);
const int CD_MASK = (L_ZENETR | L_SSHA | S_SBCF);
const int CH_MASK = (L_ZENETR);
if (tdat.sd < -900.0f) /* sd was initialized -999 as flag */ {
tdat.sd = 1.0f; /* reflag as having completed calculations */
if ((pdat.function | CD_MASK) != 0)
tdat.cd = cos(raddeg * pdat.declin);
if ((pdat.function | CH_MASK) != 0)
tdat.ch = cos(raddeg * pdat.hrang);
if ((pdat.function | CL_MASK) != 0)
tdat.cl = cos(raddeg * pdat.latitude);
if ((pdat.function | SD_MASK) != 0)
tdat.sd = sin(raddeg * pdat.declin);
if ((pdat.function | SL_MASK) != 0)
tdat.sl = sin(raddeg * pdat.latitude);
}
}
/*============================================================================
* Long integer function S_solpos, adapted from the VAX solar libraries
*
* This function calculates the apparent solar position and the
* intensity of the sun (theoretical maximum solar energy) from
* time and place on Earth.
*
* Requires (from the struct posdata parameter):
* Date and time:
* year
* daynum (requirement depends on the S_DOY switch)
* month (requirement depends on the S_DOY switch)
* day (requirement depends on the S_DOY switch)
* hour
* minute
* second
* interval DEFAULT 0
* Location:
* latitude
* longitude
* Location/time adjuster:
* timezone
* Atmospheric pressure and temperature:
* press DEFAULT 1013.0 mb
* temp DEFAULT 10.0 degrees C
* Tilt of flat surface that receives solar energy:
* aspect DEFAULT 180 (South)
* tilt DEFAULT 0 (Horizontal)
* Function Switch (codes defined in solpos.h)
* function DEFAULT S_ALL
*
* Returns (via the struct posdata parameter):
* everything defined in the struct posdata in solpos.h.
*----------------------------------------------------------------------------*/
public static long S_solpos(PosData pdat)
{
long retval;
TrigData trigdat = new TrigData();
/* initialize the trig structure */
trigdat.sd = -999.0f; /* flag to force calculation of trig data */
trigdat.cd = 1.0f;
trigdat.ch = 1.0f; /* set the rest of these to something safe */
trigdat.cl = 1.0f;
trigdat.sl = 1.0f;
if ((retval = validate(pdat)) != 0) { /* validate the inputs */
return retval;
}
if ((pdat.function & L_DOY) != 0) {
doy2dom(pdat); /* convert input doy to month-day */
} else {
dom2doy(pdat); /* convert input month-day to doy */
}
if ((pdat.function & L_GEOM) != 0) {
geometry(pdat); /* do basic geometry calculations */
}
if ((pdat.function & L_ZENETR) != 0) { /* etr at non-refracted zenith angle */
zen_no_ref(pdat, trigdat);
}
if ((pdat.function & L_SSHA) != 0) { /* Sunset hour calculation */
ssha(pdat, trigdat);
}
if ((pdat.function & L_SBCF) != 0) { /* Shadowband correction factor */
sbcf(pdat, trigdat);
}
if ((pdat.function & L_TST) != 0) { /* true solar time */
tst(pdat);
}
if ((pdat.function & L_SRSS) != 0) { /* sunrise/sunset calculations */
srss(pdat);
}
if ((pdat.function & L_SOLAZM) != 0) { /* solar azimuth calculations */
sazm(pdat, trigdat);
}
if ((pdat.function & L_REFRAC) != 0) { /* atmospheric refraction calculations */
refrac(pdat);
}
if ((pdat.function & L_AMASS) != 0) { /* airmass calculations */
amass(pdat);
}
if ((pdat.function & L_PRIME) != 0) { /* kt-prime/unprime calculations */
prime(pdat);
}
if ((pdat.function & L_ETR) != 0) { /* ETR and ETRN (refracted) */
etr(pdat);
}
if ((pdat.function & L_TILT) != 0) { /* tilt calculations */
tilt(pdat);
}
return 0;
}
/*============================================================================
* Local Void function zen_no_ref
*
* ETR solar zenith angle
* Iqbal, M. 1983. An Introduction to Solar Radiation.
* Academic Press, NY., page 15
*----------------------------------------------------------------------------*/
private static void zen_no_ref(PosData pdat, TrigData tdat)
{
float cz; /* cosine of the solar zenith angle */
localtrig(pdat, tdat);
cz = tdat.sd * tdat.sl + tdat.cd * tdat.cl * tdat.ch;
/* (watch out for the roundoff errors) */
if (fabs(cz) > 1.0f) {
if (cz >= 0.0f)
cz = 1.0f;
else
cz = -1.0f;
}
pdat.zenetr = acos(cz) * degrad;
/* (limit the degrees below the horizon to 9 [+90 . 99]) */
if (pdat.zenetr > 99.0f)
pdat.zenetr = 99.0f;
pdat.elevetr = 90.0f - pdat.zenetr;
}
