Merge 0f1a8cf into ca67e2e

satellogic · Aug 4, 2020 · a4711a6 · a4711a6
2 parents ca67e2e + 0f1a8cf
commit a4711a6
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Showing 3 changed files with 23 additions and 11 deletions.
diff --git a/orbit_predictor/predictors/base.py b/orbit_predictor/predictors/base.py
@@ -329,26 +329,21 @@ def _get_illumination(t):
 
             # If found a minimum that is not illuminated, there is an eclipse here
             if _get_illumination(eclipse_center_candidate_delta_s) < 0:
-                # The small time interval to search zeros around the center
-                # is estimated with the expected eclipse duration (which generally
-                # is smaller than expected, and that is the reason of the 1.5 coeficient).
-                # Also a minimum of 180 seconds was added because
-                # in some cases the estimation is 0 even though there is an eclipse.
-                eclipse_duration_estimation_s = self.get_eclipse_duration(start) * 60
-                zero_search_window_s = max(180, 1.5 * eclipse_duration_estimation_s)
-
                 # Search now both zeros to get the start and end of the eclipse
+                # We know that in (0, base_search_window_s) there is a minimum with negative value,
+                # and also on the opposite side of the eclipse we expect sunlight,
+                # therefore we already have two robust bracketing intervals
                 eclipse_start_delta_s = brentq(
                     _get_illumination,
-                    eclipse_center_candidate_delta_s - zero_search_window_s,
+                    eclipse_center_candidate_delta_s - orbital_period_s / 2,
                     eclipse_center_candidate_delta_s,
                     xtol=1e-2,
                     full_output=False,
                 )
                 eclipse_end_delta_s = brentq(
                     _get_illumination,
                     eclipse_center_candidate_delta_s,
-                    eclipse_center_candidate_delta_s + zero_search_window_s,
+                    eclipse_center_candidate_delta_s + orbital_period_s / 2,
                     xtol=1e-2,
                     full_output=False,
                 )

diff --git a/tests/test_numerical_predictor.py b/tests/test_numerical_predictor.py
@@ -62,7 +62,7 @@ def test_sun_sync_from_altitude_and_inclination(self):
         expected_ecc = 0.14546153131334466
 
         pred = J2Predictor.sun_synchronous(alt_km=475, inc_deg=97)
-        self.assertAlmostEqual(pred.get_position().osculating_elements[1], expected_ecc, places=15)
+        self.assertAlmostEqual(pred.get_position().osculating_elements[1], expected_ecc, places=14)
 
     def test_sun_sync_from_eccentricity_and_inclination(self):
         # Vallado 3rd edition, example 11-2

diff --git a/tests/test_predictors.py b/tests/test_predictors.py
@@ -138,3 +138,20 @@ def test_eclipses_since_finds_all_eclipses_in_a_few_orbits(sate_predictors, sate
             if get_shadow(pos, current_time) != 2:
                 assert any(ecl_start <= current_time <= ecl_end
                            for ecl_start, ecl_end in eclipses)
+
+
+@fastversion
+def test_eclipse_corner_case():
+    # See https://github.com/satellogic/orbit-predictor/issues/96
+    start = dt.datetime(2020, 9, 1)
+    end = dt.datetime(2020, 9, 2)
+    pred = J2Predictor.sun_synchronous(
+        alt_km=470.0,
+        ecc=0.001,
+        ltan_h=19,
+        ta_deg=0,
+        date=start,
+    )
+    eclipses = list(pred.eclipses_since(when_utc=start, limit_date=end))
+
+    assert len(eclipses) == 16