Implement model for local sun direction

`local_sunrise.py` renders the sky for a given time and place on earth.

2 files changed, 99 insertions, 0 deletions

diff --git a/local_sunrise.py b/local_sunrise.py
new file mode 100644
index 0000000..58ec73d
--- /dev/null
+++ b/local_sunrise.py
@@ -0,0 +1,67 @@
+import numpy as np
+import matplotlib.pyplot as plt
+from string import Template
+
+import pyopencl as cl
+from pyopencl.cltypes import make_double3
+
+mf = cl.mem_flags
+
+from planets import earth
+
+from sun import sun_direction
+from datetime import datetime
+
+config = {
+    'size_x': 1920//4,
+    'size_y': 1080//4,
+
+    'ray_samples'  : 16,
+    'light_samples': 8,
+
+    'exposure': 2.0,
+    'zoom':     1.0,
+
+    'eye_pos': np.array([0, 0, 1.0001]),
+    'eye_dir': np.array([0, 1, 0]),
+
+    'date': (2020, 1, 10),
+    'latitude': 49.01,
+    'longitude': 8.4
+}
+
+time_range = (5, 20, 1)
+
+cl_platform = cl.get_platforms()[0]
+cl_context = cl.Context(properties=[(cl.context_properties.PLATFORM, cl_platform)])
+cl_queue   = cl.CommandQueue(cl_context)
+
+cl_picture = cl.Buffer(cl_context, mf.WRITE_ONLY, size=config['size_x']*config['size_y']*3*np.float64(0).nbytes)
+program = None
+
+with open('raymarch.cl') as f:
+    program = cl.Program(cl_context, Template(f.read()).substitute(
+        {**config, **earth}
+    )).build()
+
+for time in np.arange(*time_range):
+    pit = datetime(*config['date'], int(np.floor(time)), int((time-np.floor(time))*60), 0)
+    sun_dir = sun_direction(config['latitude'], config['longitude'], pit, 1.0)
+
+    sun = make_double3(
+        np.sin(sun_dir[1])*np.cos(sun_dir[0]),
+        np.cos(sun_dir[1])*np.cos(sun_dir[0]),
+        np.sin(sun_dir[0])
+    )
+    print(sun_dir)
+
+    program.render(
+        cl_queue, (config['size_x'], config['size_y']), None, cl_picture,
+        make_double3(*(config['eye_pos'] * earth['earth_radius'])),
+        make_double3(*(config['eye_dir'] * earth['earth_radius'])),
+        sun)
+
+    np_picture = np.ndarray(shape=(config['size_y'], config['size_x'], 3), dtype=np.float64)
+    cl.enqueue_copy(cl_queue, np_picture, cl_picture).wait();
+
+    plt.imsave("sky_%05.1f.png" % time, np_picture, origin='lower')
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)