solar functions

Signed-off-by: Mattias Andrée <maandree@operamail.com>

1 files changed, 159 insertions, 0 deletions

diff --git a/src/solar.py b/src/solar.py
new file mode 100644
index 0000000..a0620bc
--- /dev/null
+++ b/src/solar.py
@@ -0,0 +1,159 @@
+#!/usr/bin/env python3
+
+# Copyright © 2014  Mattias Andrée (maandree@member.fsf.org)
+# 
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+# 
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+# 
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+import math
+import time
+
+
+def julian_day_to_epoch(t):
+    return (jd - 2440587.5) * 86400.0
+
+def epoch_to_julian_day(t):
+    return t / 86400.0 + 2440587.5
+
+def julian_day_to_julian_centuries(t):
+    return (t - 2451545.0) / 36525.0
+
+def julian_centuries_to_julian_day(t):
+    return t * 36525.0 + 2451545.0
+
+def epoch_to_julian_centuries(t):
+    return julian_day_to_julian_centuries(epoch_to_julian_day(t))
+
+def julian_centuries_to_epoch(t):
+    return julian_day_to_epoch(julian_centuries_to_julian_day(t))
+
+def epoch():
+    return time.time()
+
+def julian_day():
+    return epoch_to_julian_day(epoch())
+
+def julian_centuries():
+    return epoch_to_julian_centuries(epoch())
+
+def radians(deg):
+    return deg * math.pi / 180
+
+def degrees(rad):
+    return rad * 180 / math.pi
+
+def sun_geometric_mean_longitude(t):
+    return radians((0.0003032 * t ** 2 + 36000.76983 * t + 280.46646) % 360)
+
+def sun_geometric_mean_anomaly(t):
+    return radians(-0.0001537 * t ** 2 + 35999.05029 * t + 357.52911)
+
+def earth_orbit_eccentricity(t):
+    return -0.0000001267 * t ** 2 - 0.000042037 * t + 0.016708634
+
+def sun_equation_of_centre(t):
+    a = sun_geometric_mean_anomaly(t)
+    rc = math.sin(1 * a) * (-0.000014 * t ** 2 - 0.004817 * t + 1.914602)
+    rc += math.sin(2 * a) * (-0.000101 * t + 0.019993)
+    rc += math.sin(3 * a) * 0.000289
+    return radians(rc)
+
+def sun_real_longitude(t):
+    rc = sun_geometric_mean_longitude(t)
+    return rc + sun_equation_of_centre(t)
+
+def sun_apparent_longitude(t):
+    rc = degrees(sun_real_longitude(t)) - 0.00569
+    rc -= 0.00478 * math.sin(radians(-1934.136 * t + 125.04))
+    return radians(rc)
+
+def mean_ecliptic_obliquity(t):
+    rc = 0.001813 * t ** 3 - 0.00059 * t ** 2 - 46.815 * t + 21.448
+    rc = 26 + rc / 60
+    rc = 23 + rc / 60
+    return radians(rc)
+
+def corrected_mean_ecliptic_obliquity(t):
+    rc = -1934.136 * t + 125.04
+    rc = 0.00256 * math.cos(radians(rc))
+    rc += degrees(mean_ecliptic_obliquity(t))
+    return radians(rc)
+
+def solar_declination(t):
+    rc = math.sin(corrected_mean_ecliptic_obliquity(t))
+    rc *= math.sin(sun_apparent_longitude(t))
+    return math.asin(rc)
+
+def equation_of_time(t):
+    l = sun_geometric_mean_longitude(t)
+    e = earth_orbit_eccentricity(t)
+    m = sun_geometric_mean_anomaly(t)
+    y = corrected_mean_ecliptic_obliquity(t)
+    y = math.tan(y / 2) ** 2
+    rc = y * math.sin(2 * l)
+    rc += (4 * y * math.cos(2 * l) - 2) * e * math.sin(m)
+    rc -= 0.5 * y ** 2 * math.sin(4 * l)
+    rc -= 1.25 * e ** 2 * math.sin(2 * m)
+    return 4 * degrees(rc)
+
+def hour_angle_from_elevation(latitude, declinaton, elevation):
+    if elevation == 0:
+        return 0
+    rc = math.cos(abs(elevation))
+    rc -= math.sin(radians(latitude)) * math.sin(declinaton)
+    rc /= math.cos(radians(latitude)) * math.cos(declinaton)
+    rc = math.acos(rc)
+    return -rc if (rc < 0) == (elevation < 0) else rc;
+
+def elevation_from_hour_angle(latitude, declinaton, hour_angle):
+    rc = math.cos(radians(latitude))
+    rc *= math.cos(hour_angle) * math.cos(declinaton)
+    rc += math.sin(radians(latitude)) * math.sin(declinaton)
+    return math.asin(rc)
+
+def time_of_solar_noon(t, longitude):
+    t, rc = julian_centuries_to_julian_day(t), longitude
+    for (k, m) in ((-360, 0), (1440, -0.5)):
+        rc = julian_day_to_julian_centuries(t + m + rc / k)
+        rc = 720 - 4 * longitude - equation_of_time(rc)
+    return rc
+
+def time_of_solar_elevation(t, noon, latitude, longitude, elevation):
+    rc = noon
+    rc, et = solar_declination(rc), equation_of_time(rc)
+    rc = hour_angle_from_elevation(latitude, rc, elevation)
+    rc = 720 - 4 * (longitude + degrees(rc)) - et
+    
+    rc = julian_day_to_julian_centuries(julian_centuries_to_julian_day(t) + rc / 1440)
+    rc, et = solar_declination(rc), equation_of_time(rc)
+    rc = hour_angle_from_elevation(latitude, rc, elevation)
+    rc = 720 - 4 * (longitude + degrees(rc)) - et
+    return rc
+
+def solar_elevation_from_time(t, latitude, longitude):
+    rc = julian_centuries_to_julian_day(t)
+    rc = (rc - float(int(rc + 0.5)) - 0.5) * 1440
+    rc = 720 - rc - equation_of_time(t)
+    rc = radians(rc / 4 - longitude)
+    return elevation_from_hour_angle(latitude, solar_declination(t), rc)
+
+def solar_elevation(latitude, longitude, t = None):
+    rc = julian_centuries() if t is None else t
+    rc = solar_elevation_from_time(rc, latitude, longitude)
+    return degrees(rc)
+
+def sun(latitude, longitude, t = None, low = -6.0, high = 3.0):
+    t = julian_centuries() if t is None else t
+    e = solar_elevation(latitude, longitude, t)
+    e = (e - low) / (high - low)
+    return min(max(0, e), 1)
+