From 1d4b7059aa969875dbd4904c8a6980afdb39f647 Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Fri, 10 Jan 2020 18:10:35 +0100
Subject: Implement model for local sun direction

`local_sunrise.py` renders the sky for a given time and place on earth.
---
 sun.py | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
 create mode 100644 sun.py

(limited to 'sun.py')

diff --git a/sun.py b/sun.py
new file mode 100644
index 0000000..87bc8a9
--- /dev/null
+++ b/sun.py
@@ -0,0 +1,32 @@
+import numpy as np
+from datetime import datetime
+
+## Sun direction depending on time and place
+# As described in Appendix D of "ME 4131 Thermal Environmental Engineering Laboratory Manual"
+
+def sun_declination(time):
+    day_of_year = time.timetuple().tm_yday
+    return 23.45 * np.sin(np.radians((360/365)*(284+day_of_year)))
+
+def equation_of_time(time):
+    day_of_year = time.timetuple().tm_yday
+    b = np.radians(360*(day_of_year-81)/364)
+    return 0.165*np.sin(2*b) - 0.126*np.cos(b) - 0.025*np.sin(b)
+
+def sun_direction(lat, lon, time, time_diff, summertime_shift = 0):
+    lon_std = time_diff * 15
+    clock_time       = time.hour + time.minute/60
+    local_solar_time = clock_time + (1/15)*(lon - lon_std) + equation_of_time(time) - summertime_shift
+    hour_angle = 15*(local_solar_time - 12)
+
+    l = np.radians(lat)
+    h = np.radians(hour_angle)
+    d = np.radians(sun_declination(time))
+
+    altitude = np.arcsin(np.cos(l) * np.cos(h) * np.cos(d) + np.sin(l) * np.sin(d))
+    azimuth  = np.arccos((np.cos(d) * np.sin(l) * np.cos(h) - np.sin(d) * np.cos(l)) / np.cos(altitude))
+
+    if (time.timetuple().tm_hour <= 12):
+        return (altitude, -azimuth)
+    else:
+        return (altitude,  azimuth)
-- 
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