Changed azimuth angle range to ]-180, 180]

doc/source/api.rst

@@ -73,7 +73,7 @@ Computation of angles
  :members:
  :undoc-members:
 
-The azimuth angles are calculated using get_alt_az and get_observer_look from pyorbital. In pyorbital documentation there is a link describing how calculations are done http://celestrak.com/columns/v02n02/. The azimuth described in the link is measured as clockwise from North instead of counter-clockwise from South. Counter clockwise from south would be the standard for a right-handed orthogonal coordinate system. Pygac was updated to use the same definition for angles as pyorbital (20190926, version 1.1.0). Previous versions used azimuth +/-180 degrees, which correspond to degrees clockwise from south. All angles are converted to degrees.
+The azimuth angles are calculated using get_alt_az and get_observer_look from pyorbital. In pyorbital documentation there is a link describing how calculations are done http://celestrak.com/columns/v02n02/. The azimuth described in the link is measured as clockwise from North instead of counter-clockwise from South. Counter clockwise from south would be the standard for a right-handed orthogonal coordinate system. Pygac was updated to use the same definition for angles as pyorbital (2019, September, version > 1.1.0). Previous versions used azimuth +/-180 degrees, which correspond to degrees clockwise from south. All angles are converted to degrees. All azimuth angles are converted to range ]-180, 180] (2019 October version > 1.1.0). Note that ]-180, 180] is an open interval.
 
 
 GAC calibration/inter-calibration

pygac/__init__.py

@@ -45,3 +45,10 @@ def get_absolute_azimuth_angle_diff(sat_azi, sun_azi):
  # Not using np.where to avoid copying array
  rel_azi[rel_azi > 180] = 360.0 - rel_azi[rel_azi > 180]
  return rel_azi
+
+
+def centered_modulus(array, divisor):
+ """Transform array to half open range ]-divisor/2, divisor/2]."""
+ arr = array % divisor
+ arr[arr > divisor / 2] -= divisor
+ return arr

pygac/gac_reader.py

@@ -30,7 +30,8 @@
 import six
 import types
 
-from pygac import CONFIG_FILE, get_absolute_azimuth_angle_diff
+from pygac import (CONFIG_FILE, centered_modulus,
+ get_absolute_azimuth_angle_diff)
 try:
  import ConfigParser
 except ImportError:
@@ -452,6 +453,23 @@ def get_tle_lines(self):
  return tle1, tle2
 
  def get_angles(self):
+ """Get azimuth and zenith angles.
+
+ Azimuth angle definition is the same as in pyorbital, but with
+ different units (degrees not radians for sun azimuth angles)
+ and different ranges.
+
+ Returns:
+ sat_azi: satellite azimuth angle
+ degree clockwise from north in range ]-180, 180],
+ sat_zentih: satellite zenith angles in degrees in range [0,90],
+ sun_azi: sun azimuth angle
+ degree clockwise from north in range ]-180, 180],
+ sun_zentih: sun zenith angles in degrees in range [0,90],
+ rel_azi: absolute azimuth angle difference in degrees between sun
+ and sensor in range [0, 180]
+
+ """
  self.get_times()
  self.get_lonlat()
  tle1, tle2 = self.get_tle_lines()
@@ -472,6 +490,10 @@ def get_angles(self):
  sun_azi = np.rad2deg(sun_azi)
  rel_azi = get_absolute_azimuth_angle_diff(sun_azi, sat_azi)
 
+ # Scale angles range to half open interval ]-180, 180]
+ sat_azi = centered_modulus(sat_azi, 360.0)
+ sun_azi = centered_modulus(sun_azi, 360.0)
+
  # Mask corrupt scanlines
  for arr in (sat_azi, sat_zenith, sun_azi, sun_zenith, rel_azi):
  arr[self.mask] = np.nan

pygac/tests/test_angles.py

@@ -27,7 +27,8 @@
 
 import numpy as np
 
-from pygac import get_absolute_azimuth_angle_diff
+from pygac import (get_absolute_azimuth_angle_diff,
+ centered_modulus)
 
 
 class TestAngles(unittest.TestCase):
@@ -53,10 +54,24 @@ def test_azidiff_angle(self):
 
  np.testing.assert_allclose(rel_azi, res)
 
+ def test_centered_modulus(self):
+ """Test centered_modulus."""
+ angles = np.ma.array(
+ [[180.0, -180.0, -179.9, 201.0],
+ [80.0, 360.0, -360.0, 604.0],
+ [-80.0, -88.0, -796.0, -104.0],
+ [-3.0, -188.0, -196.0, -204.0]], mask=False)
+ expected = np.ma.array(
+ [[180.0, 180.0, -179.9, -159.0],
+ [80.0, 0.0, 0.0, -116.0],
+ [-80.0, -88.0, -76.0, -104.0],
+ [-3.0, 172.0, 164.0, 156.0]], mask=False)
+ transformed = centered_modulus(angles, 360.0)
+ np.testing.assert_allclose(transformed, expected)
+
 
 def suite():
- """The suite for test_slerp
- """
+ """Test suite for test_angles."""
  loader = unittest.TestLoader()
  mysuite = unittest.TestSuite()
  mysuite.addTest(loader.loadTestsFromTestCase(TestAngles))

pygac/tests/test_reader.py

@@ -65,7 +65,6 @@ def test_get_lonlat(self, interpolator, adjust_clockdrift,
  lat_i = np.array([1, 2, 3, np.nan, -90.1, 90.1])
  get_lonlat.return_value = lon_i, lat_i
  interpolator.return_value = lon_i, lat_i
-
  get_corrupt_mask.return_value = np.array(
  [0, 0, 1, 0, 0, 0], dtype=bool)
 
@@ -192,9 +191,50 @@ def test_get_tle_lines(self, read_tle_file, *mocks):
  self.assertEqual(tle1, tle_data[tle_idx])
  self.assertEqual(tle2, tle_data[tle_idx + 1])
 
+ @mock.patch('pygac.gac_reader.GACReader._get_corrupt_mask')
+ def test_get_angles(self, get_corrupt_mask):
+ """Test get_angles function of the reader."""
+ # Line: 1, 649, 6198 and 12658 from Tiros-N file (1980-01-03 11:47)
+ lon_i = np.array(
+ [69.41555, 152.10587, 164.3131, 67.23855, np.nan])[:, np.newaxis]
+ lat_i = np.array(
+ [71.6283, 85.24265, -62.076958, 82.72296, np.nan])[:, np.newaxis]
+ get_corrupt_mask.return_value = np.isnan(lon_i)
+ self.reader.lons = lon_i
+ self.reader.lats = lat_i
+ self.reader.tle_lines = [
+ '1 11060U 78096A 80003.54792075 .00000937 00000-0 52481-3 0 2588\r\n', # noqa
+ '2 11060 98.9783 332.1605 0012789 88.8047 271.4583 14.11682873 63073\r\n'] # noqa
+ self.reader.utcs = np.array(
+ [315748035469, 315748359969,
+ 315751135469, 315754371969,
+ 315754371969]).astype('datetime64[ms]')
+ self.reader.spacecrafts_orbital = {25: 'tiros n'}
+ self.reader.spacecraft_id = 25
+ self.reader.times = self.reader.to_datetime(self.reader.utcs)
+ expected_sat_azi = np.array(
+ [-76.90, 11.08, 145.33, -50.01, np.nan])[:, np.newaxis]
+ expected_sun_azi = np.array(
+ [-120.36, -31.94, -173.51, -93.67, np.nan])[:, np.newaxis]
+ expected_sat_zenith = np.array(
+ [69.05, 69.04, 69.55, 69.07, np.nan])[:, np.newaxis]
+ expected_sun_zenith = np.array(
+ [104.30, 116.94, 94.86, 112.60, np.nan])[:, np.newaxis]
+ expected_rel_azi = np.array(
+ [43.45, 43.01, 41.16, 43.65, np.nan])[:, np.newaxis]
+
+ retv = self.reader.get_angles()
+ (sat_azi, sat_zenith, sun_azi, sun_zenith, rel_azi) = retv
+ np.testing.assert_allclose(sat_azi, expected_sat_azi, atol=0.01)
+ np.testing.assert_allclose(sun_azi, expected_sun_azi, atol=0.01)
+ np.testing.assert_allclose(sat_zenith, expected_sat_zenith, atol=0.01)
+ np.testing.assert_allclose(sun_zenith, expected_sun_zenith, atol=0.01)
+ np.testing.assert_allclose(rel_azi, expected_rel_azi, atol=0.01)
+
  @mock.patch('pygac.gac_reader.ConfigParser.ConfigParser.read')
  @mock.patch('pygac.gac_reader.ConfigParser.ConfigParser.items')
  def test_get_tle_file(self, items, *mocks):
+ """Test get_tle_file."""
  # Use TLE name/dir from config file
  items.return_value = [('tledir', 'a'), ('tlename', 'b')]
  tle_file = self.reader.get_tle_file()