better nan handling in singleaxis (#697)

wholmgren · web-flow · commit c9adf8b062d6 · 2019-05-03T07:16:13.000-07:00
* better nan handling in singleaxis

* a couple of comments
diff --git a/docs/sphinx/source/whatsnew/v0.6.2.rst b/docs/sphinx/source/whatsnew/v0.6.2.rst
@@ -41,7 +41,11 @@ Bug fixes
 * Fixed :py:func:`~pvlib.irradiance.erbs` behavior when zenith is
   near 90 degrees. (:issue:`681`)
 * :py:func:`~pvlib.irradiance.dni` now referenced in API under
-  Decomposing and Combining irradiance header. (:issue:`686`)  
+  Decomposing and Combining irradiance header. (:issue:`686`)
+* Fixed NaN output from :py:func:`~pvlib.tracking.singleaxis` when sun
+  near horizon. (:issue:`656`)
+* Fixed numpy warnings in :py:func:`~pvlib.tracking.singleaxis` when
+  comparing NaN values to limits. (:issue:`622`)
 
 
 Testing
@@ -54,4 +58,5 @@ Contributors
 * Will Holmgren (:ghuser:`wholmgren`)
 * Roel Loonen (:ghuser:`roelloonen`)
 * Todd Hendricks (:ghuser:`tahentx`)
-
+* Kevin Anderson (:ghuser:`kevinsa5`)
+* :ghuser:`bentomlinson`
diff --git a/pvlib/test/test_tracking.py b/pvlib/test/test_tracking.py
@@ -1,5 +1,3 @@
-import datetime
-
 import numpy as np
 from numpy import nan
 import pandas as pd
@@ -96,10 +94,10 @@ def test_arrays_multi():
     apparent_azimuth = np.array([[180, 180], [180, 180]])
     # singleaxis should fail for num dim > 1
     with pytest.raises(ValueError):
-        tracker_data = tracking.singleaxis(apparent_zenith, apparent_azimuth,
-                                           axis_tilt=0, axis_azimuth=0,
-                                           max_angle=90, backtrack=True,
-                                           gcr=2.0/7.0)
+        tracking.singleaxis(apparent_zenith, apparent_azimuth,
+                            axis_tilt=0, axis_azimuth=0,
+                            max_angle=90, backtrack=True,
+                            gcr=2.0/7.0)
     # uncomment if we ever get singleaxis to support num dim > 1 arrays
     # assert isinstance(tracker_data, dict)
     # expect = {'tracker_theta': np.full_like(apparent_zenith, 0),
@@ -121,7 +119,7 @@ def test_azimuth_north_south():
 
     expect = pd.DataFrame({'tracker_theta': -60, 'aoi': 0,
                            'surface_azimuth': 90, 'surface_tilt': 60},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -146,7 +144,7 @@ def test_max_angle():
 
     expect = pd.DataFrame({'aoi': 15, 'surface_azimuth': 90,
                            'surface_tilt': 45, 'tracker_theta': 45},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -163,7 +161,7 @@ def test_backtrack():
 
     expect = pd.DataFrame({'aoi': 0, 'surface_azimuth': 90,
                            'surface_tilt': 80, 'tracker_theta': 80},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -175,7 +173,7 @@ def test_backtrack():
 
     expect = pd.DataFrame({'aoi': 52.5716, 'surface_azimuth': 90,
                            'surface_tilt': 27.42833, 'tracker_theta': 27.4283},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -193,7 +191,7 @@ def test_axis_tilt():
     expect = pd.DataFrame({'aoi': 7.286245, 'surface_azimuth': 142.65730,
                            'surface_tilt': 35.98741,
                            'tracker_theta': -20.88121},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -205,7 +203,7 @@ def test_axis_tilt():
 
     expect = pd.DataFrame({'aoi': 47.6632, 'surface_azimuth': 50.96969,
                            'surface_tilt': 42.5152, 'tracker_theta': 31.6655},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -222,7 +220,7 @@ def test_axis_azimuth():
 
     expect = pd.DataFrame({'aoi': 30, 'surface_azimuth': 180,
                            'surface_tilt': 0, 'tracker_theta': 0},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -237,7 +235,7 @@ def test_axis_azimuth():
 
     expect = pd.DataFrame({'aoi': 0, 'surface_azimuth': 180,
                            'surface_tilt': 30, 'tracker_theta': 30},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
@@ -277,6 +275,20 @@ def test_horizon_tilted():
     assert_frame_equal(out, expected)
 
 
+def test_low_sun_angles():
+    # GH 656
+    result = tracking.singleaxis(
+        apparent_zenith=80, apparent_azimuth=338, axis_tilt=30,
+        axis_azimuth=180, max_angle=60, backtrack=True, gcr=0.35)
+    expected = {
+        'tracker_theta': np.array([-50.31051385]),
+        'aoi': np.array([61.35300178]),
+        'surface_azimuth': np.array([112.53615425]),
+        'surface_tilt': np.array([56.42233095])}
+    for k, v in result.items():
+        assert_allclose(expected[k], v)
+
+
 def test_SingleAxisTracker_creation():
     system = tracking.SingleAxisTracker(max_angle=45,
                                         gcr=.25,
@@ -299,37 +311,35 @@ def test_SingleAxisTracker_tracking():
 
     tracker_data = system.singleaxis(apparent_zenith, apparent_azimuth)
 
-    expect = pd.DataFrame({'aoi': 7.286245, 'surface_azimuth': 142.65730 ,
+    expect = pd.DataFrame({'aoi': 7.286245, 'surface_azimuth': 142.65730,
                            'surface_tilt': 35.98741,
                            'tracker_theta': -20.88121},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
 
-    ### results calculated using PVsyst
+    # results calculated using PVsyst
     pvsyst_solar_azimuth = 7.1609
     pvsyst_solar_height = 27.315
     pvsyst_axis_tilt = 20.
     pvsyst_axis_azimuth = 20.
-    pvsyst_system = tracking.SingleAxisTracker(max_angle=60.,
-                                               axis_tilt=pvsyst_axis_tilt,
-                                               axis_azimuth=180+pvsyst_axis_azimuth,
-                                               backtrack=False)
+    pvsyst_system = tracking.SingleAxisTracker(
+        max_angle=60., axis_tilt=pvsyst_axis_tilt,
+        axis_azimuth=180+pvsyst_axis_azimuth, backtrack=False)
     # the definition of azimuth is different from PYsyst
     apparent_azimuth = pd.Series([180+pvsyst_solar_azimuth])
     apparent_zenith = pd.Series([90-pvsyst_solar_height])
     tracker_data = pvsyst_system.singleaxis(apparent_zenith, apparent_azimuth)
-    expect = pd.DataFrame({'aoi': 41.07852 , 'surface_azimuth': 180-18.432,
-                           'surface_tilt': 24.92122 ,
+    expect = pd.DataFrame({'aoi': 41.07852, 'surface_azimuth': 180-18.432,
+                           'surface_tilt': 24.92122,
                            'tracker_theta': -15.18391},
-                           index=[0], dtype=np.float64)
+                          index=[0], dtype=np.float64)
     expect = expect[SINGLEAXIS_COL_ORDER]
 
     assert_frame_equal(expect, tracker_data)
 
 
-
 def test_LocalizedSingleAxisTracker_creation():
     localized_system = tracking.LocalizedSingleAxisTracker(latitude=32,
                                                            longitude=-111,
diff --git a/pvlib/tracking.py b/pvlib/tracking.py
@@ -441,19 +441,22 @@ def singleaxis(apparent_zenith, apparent_azimuth,
     # angle convention being used here.
     if backtrack:
         axes_distance = 1/gcr
-        temp = np.minimum(axes_distance*cosd(wid), 1)
+        # clip needed for low angles. GH 656
+        temp = np.clip(axes_distance*cosd(wid), -1, 1)
 
         # backtrack angle
         # (always positive b/c acosd returns values between 0 and 180)
         wc = np.degrees(np.arccos(temp))
 
         # Eq 4 applied when wid in QIV (wid < 0 evalulates True), QI
-        tracker_theta = np.where(wid < 0, wid + wc, wid - wc)
+        with np.errstate(invalid='ignore'):
+            # errstate for GH 622
+            tracker_theta = np.where(wid < 0, wid + wc, wid - wc)
     else:
         tracker_theta = wid
 
-    tracker_theta[tracker_theta > max_angle] = max_angle
-    tracker_theta[tracker_theta < -max_angle] = -max_angle
+    tracker_theta = np.minimum(tracker_theta, max_angle)
+    tracker_theta = np.maximum(tracker_theta, -max_angle)
 
     # calculate panel normal vector in panel-oriented x, y, z coordinates.
     # y-axis is axis of tracker rotation.  tracker_theta is a compass angle
@@ -560,8 +563,9 @@ def singleaxis(apparent_zenith, apparent_azimuth,
     surface_azimuth = 90 - surface_azimuth + axis_azimuth
 
     # 5. Map azimuth into [0,360) domain.
-    surface_azimuth[surface_azimuth < 0] += 360
-    surface_azimuth[surface_azimuth >= 360] -= 360
+    # surface_azimuth[surface_azimuth < 0] += 360
+    # surface_azimuth[surface_azimuth >= 360] -= 360
+    surface_azimuth = surface_azimuth % 360
 
     # Calculate surface_tilt
     dotproduct = (panel_norm_earth * projected_normal).sum(axis=1)
