Sunrise and sunset times based on coordinates and altitude - c++

Question

I am using this code for calculating sunrise and sunset times.
// Get the daylight status of the current time.
bool
SunLight::CalculateDaylightStatus()
{
// Calculate the current time of day.
time_t currentTime = time(NULL);
m_LocalTime = localtime(&currentTime);
// Initialize the sunrise and set times.
*m_Sunrise = *m_LocalTime;
*m_Sunset = *m_LocalTime;
// Flags to check whether sunrise or set available on the day or not.
m_IsSunrise = false;
m_IsSunset = false;
m_RiseAzimuth = 0.0;
m_SetAzimuth = 0.0;
for (unsigned int i = 0; i < 3; i++)
{
m_RightAscention[i] = 0.0;
m_Decension[i] = 0.0;
m_VHz[i] = 0.0;
}
for (unsigned int i = 0; i < 2; i++)
{
m_SunPositionInSky[i] = 0.0;
m_RiseTime[i] = 0;
m_SetTime[i] = 0;
}
// Calculate the sunrise and set times.
CalculateSunRiseSetTimes();
return (mktime(m_LocalTime) >= mktime(m_Sunrise) && mktime(m_LocalTime) < mktime(m_Sunset))
? true
: false;
}
//---------------------------------------------------------------------
bool
SunLight::CalculateSunRiseSetTimes()
{
double zone = timezone/3600 - m_LocalTime->tm_isdst;
// Julian day relative to Jan 1.5, 2000.
double jd = GetJulianDay() - 2451545;
if ((Sign(zone) == Sign(m_Config->Longitude())) && (zone != 0))
{
return false;
}
double tz = zone / 24;
// Centuries since 1900.0
double ct = jd / 36525 + 1;
// Local sidereal time.
double t0 = LocalSiderealTimeForTimeZone(jd, tz, m_Config->Longitude()/360);
// Get sun position at start of day.
jd += tz;
// Calculate the position of the sun.
CalculateSunPosition(jd, ct);
double ra0 = m_SunPositionInSky[0];
double dec0 = m_SunPositionInSky[1];
// Get sun position at end of day.
jd += 1;
// Calculate the position of the sun.
CalculateSunPosition(jd, ct);
double ra1 = m_SunPositionInSky[0];
double dec1 = m_SunPositionInSky[1];
// make continuous
if (ra1 < ra0)
ra1 += 2 * M_PI;
m_RightAscention[0] = ra0;
m_Decension[0] = dec0;
// check each hour of this day
for (int k = 0; k < 24; k++)
{
m_RightAscention[2] = ra0 + (k + 1) * (ra1 - ra0) / 24;
m_Decension[2] = dec0 + (k + 1) * (dec1 - dec0) / 24;
m_VHz[2] = TestHour(k, t0, m_Config->Latitude());
// advance to next hour
m_RightAscention[0] = m_RightAscention[2];
m_Decension[0] = m_Decension[2];
m_VHz[0] = m_VHz[2];
}
// Update the tm structure with time values.
m_Sunrise->tm_hour = m_RiseTime[0];
m_Sunrise->tm_min = m_RiseTime[1];
m_Sunset->tm_hour = m_SetTime[0];
m_Sunset->tm_min = m_SetTime[1];
// neither sunrise nor sunset
if ((!m_IsSunrise) && (!m_IsSunset))
{
// Sun down all day.
if (m_VHz[2] < 0)
m_IsSunset = true;
// Sun up all day.
else
m_IsSunrise = true;
}
return true;
}
//---------------------------------------------------------------------
int
SunLight::Sign(double value)
{
if (value > 0.0)
return 1;
else if (value < 0.0)
return -1;
else
return 0;
}
//---------------------------------------------------------------------
// Local Sidereal Time for zone.
double
SunLight::LocalSiderealTimeForTimeZone(double jd, double z, double lon)
{
double s = 24110.5 + 8640184.812999999 * jd / 36525 + 86636.6 * z + 86400 * lon;
s = s / 86400;
s = s - floor(s);
return s * 360 * cDegToRad;
}
//---------------------------------------------------------------------
// Determine Julian day from calendar date
// (Jean Meeus, "Astronomical Algorithms", Willmann-Bell, 1991).
double
SunLight::GetJulianDay()
{
int month = m_LocalTime->tm_mon + 1;
int day = m_LocalTime->tm_mday;
int year = 1900 + m_LocalTime->tm_year;
bool gregorian = (year < 1583) ? false : true;
if ((month == 1) || (month == 2))
{
year = year - 1;
month = month + 12;
}
double a = floor((double)year / 100);
double b = 0;
if (gregorian)
b = 2 - a + floor(a / 4);
else
b = 0.0;
double jd = floor(365.25 * (year + 4716))
+ floor(30.6001 * (month + 1))
+ day + b - 1524.5;
return jd;
}
//---------------------------------------------------------------------
// Sun's position using fundamental arguments
// (Van Flandern & Pulkkinen, 1979).
void
SunLight::CalculateSunPosition(double jd, double ct)
{
double g, lo, s, u, v, w;
lo = 0.779072 + 0.00273790931 * jd;
lo = lo - floor(lo);
lo = lo * 2 * M_PI;
g = 0.993126 + 0.0027377785 * jd;
g = g - floor(g);
g = g * 2 * M_PI;
v = 0.39785 * sin(lo);
v = v - 0.01 * sin(lo - g);
v = v + 0.00333 * sin(lo + g);
v = v - 0.00021 * ct * sin(lo);
u = 1 - 0.03349 * cos(g);
u = u - 0.00014 * cos(2 * lo);
u = u + 0.00008 * cos(lo);
w = -0.0001 - 0.04129 * sin(2 * lo);
w = w + 0.03211 * sin(g);
w = w + 0.00104 * sin(2 * lo - g);
w = w - 0.00035 * sin(2 * lo + g);
w = w - 0.00008 * ct * sin(g);
// compute sun's right ascension
s = w / sqrt(u - v * v);
m_SunPositionInSky[0] = lo + atan(s / sqrt(1 - s * s));
// ...and declination
s = v / sqrt(u);
m_SunPositionInSky[1] = atan(s / sqrt(1 - s * s));
}
//---------------------------------------------------------------------
// Test an hour for an event.
double
SunLight::TestHour(int k, double t0, double prmLatitude)
{
double ha[3];
double a, b, c, d, e, s, z;
double time;
double az, dz, hz, nz;
int hr, min;
ha[0] = t0 - m_RightAscention[0] + k * cK1;
ha[2] = t0 - m_RightAscention[2] + k * cK1 + cK1;
ha[1] = (ha[2] + ha[0]) / 2; // hour angle at half hour
m_Decension[1] = (m_Decension[2] + m_Decension[0]) / 2; // declination at half hour
s = sin(prmLatitude * cDegToRad);
c = cos(prmLatitude * cDegToRad);
z = cos(90.833 * cDegToRad); // refraction + sun semi-diameter at horizon
if (k <= 0)
m_VHz[0] = s * sin(m_Decension[0]) + c * cos(m_Decension[0]) * cos(ha[0]) - z;
m_VHz[2] = s * sin(m_Decension[2]) + c * cos(m_Decension[2]) * cos(ha[2]) - z;
if (Sign(m_VHz[0]) == Sign(m_VHz[2]))
return m_VHz[2]; // no event this hour
m_VHz[1] = s * sin(m_Decension[1]) + c * cos(m_Decension[1]) * cos(ha[1]) - z;
a = 2 * m_VHz[0] - 4 * m_VHz[1] + 2 * m_VHz[2];
b = -3 * m_VHz[0] + 4 * m_VHz[1] - m_VHz[2];
d = b * b - 4 * a * m_VHz[0];
if (d < 0)
return m_VHz[2]; // no event this hour
d = sqrt(d);
e = (-b + d) / (2 * a);
if ((e > 1) || (e < 0))
e = (-b - d) / (2 * a);
time = (double)k + e + (double)1 / (double)120; // time of an event
hr = (int)floor(time);
min = (int)floor((time - hr) * 60);
hz = ha[0] + e * (ha[2] - ha[0]); // azimuth of the sun at the event
nz = -cos(m_Decension[1]) * sin(hz);
dz = c * sin(m_Decension[1]) - s * cos(m_Decension[1]) * cos(hz);
az = atan2(nz, dz) / cDegToRad;
if (az < 0) az = az + 360;
if ((m_VHz[0] < 0) && (m_VHz[2] > 0))
{
m_RiseTime[0] = hr;
m_RiseTime[1] = min;
m_RiseAzimuth = az;
m_IsSunrise = true;
}
if ((m_VHz[0] > 0) && (m_VHz[2] < 0))
{
m_SetTime[0] = hr;
m_SetTime[1] = min;
m_SetAzimuth = az;
m_IsSunset = true;
}
return m_VHz[2];
}
//---------------------------------------------------------------------
I need to introduce altitude in the formula which gives more accurate result. Can someone give me a quick solution what I have to modify to add altitude in the formula?

Answer 1

That algorithm is nowhere near calculating the times of sunrise and sunset. What you need is Jean Meeus' book "Astronomical Algorithms". You will need to account for the observer's longitude and latitude, the difference between dynamical time and universal time, and the eccentricity of the Earth's orbit to obtain even a low accuracy result.

Answer 2

This seems to be called sunrise equation. The formulas in that Wiki article are unbelievably simple, and they do account for the geographic location.