Merge pull request #54 from ghulands/fix_issue_24

Issue 24: Fix negative azimuth values
pingswept · Aug 14, 2017 · 55debbb · 55debbb
2 parents 7a0a7b6 + b2fa4ea
commit 55debbb
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Showing 2 changed files with 14 additions and 12 deletions.
diff --git a/pysolar/solar.py b/pysolar/solar.py
@@ -100,11 +100,10 @@ def get_position(latitude_deg, longitude_deg, when, elevation=0,
     refraction_correction = get_refraction_correction(pressure, temperature,
                                                       topocentric_elevation_angle)
 
-    altitude_deg =  topocentric_elevation_angle + refraction_correction
+    altitude_deg = topocentric_elevation_angle + refraction_correction
 
-    azimuth_deg = (180 -
-        get_topocentric_azimuth_angle(topocentric_local_hour_angle,
-                                      latitude_deg, topocentric_sun_declination))
+    azimuth_deg = get_topocentric_azimuth_angle(topocentric_local_hour_angle,
+                                      latitude_deg, topocentric_sun_declination)
 
     return azimuth_deg, altitude_deg
 
@@ -141,9 +140,8 @@ def get_azimuth(latitude_deg, longitude_deg, when, elevation = 0):
     topocentric_sun_declination, topocentric_local_hour_angle = \
         get_topocentric_position(latitude_deg, longitude_deg, when, elevation)
 
-    azimuth = (180 -
-        get_topocentric_azimuth_angle(topocentric_local_hour_angle,
-            latitude_deg, topocentric_sun_declination))
+    azimuth = get_topocentric_azimuth_angle(topocentric_local_hour_angle,
+            latitude_deg, topocentric_sun_declination)
 
     return azimuth
 
@@ -342,13 +340,13 @@ def get_solar_time(longitude_deg, when):
 # Topocentric functions calculate angles relative to a location on the surface of the earth.
 
 def get_topocentric_azimuth_angle(topocentric_local_hour_angle, latitude, topocentric_sun_declination):
-    """Measured eastward from north"""
+    """West is negative, East is positive, Masters p. 395"""
     tlha_rad = math.radians(topocentric_local_hour_angle)
     latitude_rad = math.radians(latitude)
     tsd_rad = math.radians(topocentric_sun_declination)
     a = math.sin(tlha_rad)
     b = math.cos(tlha_rad) * math.sin(latitude_rad) - math.tan(tsd_rad) * math.cos(latitude_rad)
-    return 180.0 + math.degrees(math.atan2(a, b)) % 360
+    return (180.0 + math.degrees(math.atan2(a, b))) % 360
 
 def get_topocentric_elevation_angle(latitude, topocentric_sun_declination, topocentric_local_hour_angle):
     latitude_rad = math.radians(latitude)

diff --git a/test/testsolar.py b/test/testsolar.py
@@ -161,13 +161,17 @@ class TestApi(unittest.TestCase):
 	test_when = datetime.datetime(2016, 12, 19, 23, 0, 0, tzinfo=datetime.timezone.utc )
 
 	def testGetPosition(self):
+		az, al = solar.get_position(59.6365662,12.5350953, TestApi.test_when)
+		self.assertAlmostEqual(az, 357.1496112)
+		self.assertAlmostEqual(al, -53.7673267)
+
 		az, al = solar.get_position(-43, 172, TestApi.test_when)
-		self.assertAlmostEqual(az, -230.4936927)
+		self.assertAlmostEqual(az, 50.4936927)
 		self.assertAlmostEqual(al, 63.0945557)
 
 		# From Greenwich
 		az, al = solar.get_position(51.4826, 0, TestApi.test_when)
-		self.assertAlmostEqual(az, -153.0476242)
+		self.assertAlmostEqual(az, 333.0476242)
 		self.assertAlmostEqual(al, -59.8384205)
 
 	def testGetAltitude(self):
@@ -176,7 +180,7 @@ def testGetAltitude(self):
 
 	def testGetAzimuth(self):
 		az = solar.get_azimuth(-43, 172, TestApi.test_when)
-		self.assertAlmostEqual(az, -230.4936927)
+		self.assertAlmostEqual(az, 50.4936927)
 
 
 if __name__ == "__main__":