Fix IncompatibleArgumentsError on Moon's observation events

On some dates, `Moon#observation_events` would throw a `IncompatibleArgumentsError`. This was due to the interpolation method. It takes 3 or 5 approximately equidistant values and interpolate a value between them. Because angles are normalized, an angle that would be 365° would be normalized into 5°. While it makes sense in the library, it breaks the suite of numbers when using interpolation. A list that would initially and logically be `[345, 355, 365]` is changed into `[345, 355, 5]`, which makes the interpolation logic wrong. This fixes this issue by denormalizing values for interpolation when it seems it is needed. When we have consecutive values that are suddenly very far from each other, the method will fix them so that the suite stays uniform. To be honest, this seems a bit hacky and I have no way of making sure this actually works fine without adding tons and tons of new examples with different configurations and making sure the results still make sense. But the library is already quite well test-covered and everything is green, so I guess this new method is fine. Fixes #106
rhannequin · Nov 24, 2024 · 0287959 · 0287959
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diff --git a/lib/astronoby/events/observation_events.rb b/lib/astronoby/events/observation_events.rb
@@ -221,11 +221,13 @@ def rationalize_decimal_hours(decimal_hours)
       def right_ascension_transit
         Angle.from_degrees(
           Util::Maths.interpolate(
-            [
-              @coordinates_of_the_previous_day.right_ascension.degrees,
-              @coordinates_of_the_day.right_ascension.degrees,
-              @coordinates_of_the_next_day.right_ascension.degrees
-            ],
+            Util::Maths.normalize_angles_for_interpolation(
+              [
+                @coordinates_of_the_previous_day.right_ascension.degrees,
+                @coordinates_of_the_day.right_ascension.degrees,
+                @coordinates_of_the_next_day.right_ascension.degrees
+              ]
+            ),
             (@final_transit || @initial_transit) + leap_day_portion
           )
         )
@@ -234,11 +236,13 @@ def right_ascension_transit
       def declination_rising
         Angle.from_degrees(
           Util::Maths.interpolate(
-            [
-              @coordinates_of_the_previous_day.declination.degrees,
-              @coordinates_of_the_day.declination.degrees,
-              @coordinates_of_the_next_day.declination.degrees
-            ],
+            Util::Maths.normalize_angles_for_interpolation(
+              [
+                @coordinates_of_the_previous_day.declination.degrees,
+                @coordinates_of_the_day.declination.degrees,
+                @coordinates_of_the_next_day.declination.degrees
+              ]
+            ),
             @final_rising + leap_day_portion
           )
         )
@@ -247,11 +251,13 @@ def declination_rising
       def declination_transit
         Angle.from_degrees(
           Util::Maths.interpolate(
-            [
-              @coordinates_of_the_previous_day.declination.degrees,
-              @coordinates_of_the_day.declination.degrees,
-              @coordinates_of_the_next_day.declination.degrees
-            ],
+            Util::Maths.normalize_angles_for_interpolation(
+              [
+                @coordinates_of_the_previous_day.declination.degrees,
+                @coordinates_of_the_day.declination.degrees,
+                @coordinates_of_the_next_day.declination.degrees
+              ]
+            ),
             (@final_transit || @initial_transit) + leap_day_portion
           )
         )
@@ -260,11 +266,13 @@ def declination_transit
       def declination_setting
         Angle.from_degrees(
           Util::Maths.interpolate(
-            [
-              @coordinates_of_the_previous_day.declination.degrees,
-              @coordinates_of_the_day.declination.degrees,
-              @coordinates_of_the_next_day.declination.degrees
-            ],
+            Util::Maths.normalize_angles_for_interpolation(
+              [
+                @coordinates_of_the_previous_day.declination.degrees,
+                @coordinates_of_the_day.declination.degrees,
+                @coordinates_of_the_next_day.declination.degrees
+              ]
+            ),
             @final_setting + leap_day_portion
           )
         )

diff --git a/lib/astronoby/events/rise_transit_set_iteration.rb b/lib/astronoby/events/rise_transit_set_iteration.rb
@@ -150,11 +150,13 @@ def local_horizontal_altitude_setting
     def right_ascension_rising
       Angle.from_degrees(
         Util::Maths.interpolate(
-          [
-            @coordinates_of_the_previous_day.right_ascension.degrees,
-            @coordinates_of_the_day.right_ascension.degrees,
-            @coordinates_of_the_next_day.right_ascension.degrees
-          ],
+          Util::Maths.normalize_angles_for_interpolation(
+            [
+              @coordinates_of_the_previous_day.right_ascension.degrees,
+              @coordinates_of_the_day.right_ascension.degrees,
+              @coordinates_of_the_next_day.right_ascension.degrees
+            ]
+          ),
           @initial_rising + leap_day_portion
         )
       )
@@ -163,11 +165,13 @@ def right_ascension_rising
     def right_ascension_transit
       Angle.from_degrees(
         Util::Maths.interpolate(
-          [
-            @coordinates_of_the_previous_day.right_ascension.degrees,
-            @coordinates_of_the_day.right_ascension.degrees,
-            @coordinates_of_the_next_day.right_ascension.degrees
-          ],
+          Util::Maths.normalize_angles_for_interpolation(
+            [
+              @coordinates_of_the_previous_day.right_ascension.degrees,
+              @coordinates_of_the_day.right_ascension.degrees,
+              @coordinates_of_the_next_day.right_ascension.degrees
+            ]
+          ),
           @initial_transit + leap_day_portion
         )
       )
@@ -176,11 +180,13 @@ def right_ascension_transit
     def right_ascension_setting
       Angle.from_degrees(
         Util::Maths.interpolate(
-          [
-            @coordinates_of_the_previous_day.right_ascension.degrees,
-            @coordinates_of_the_day.right_ascension.degrees,
-            @coordinates_of_the_next_day.right_ascension.degrees
-          ],
+          Util::Maths.normalize_angles_for_interpolation(
+            [
+              @coordinates_of_the_previous_day.right_ascension.degrees,
+              @coordinates_of_the_day.right_ascension.degrees,
+              @coordinates_of_the_next_day.right_ascension.degrees
+            ]
+          ),
           @initial_setting + leap_day_portion
         )
       )
@@ -189,11 +195,13 @@ def right_ascension_setting
     def declination_rising
       Angle.from_degrees(
         Util::Maths.interpolate(
-          [
-            @coordinates_of_the_previous_day.declination.degrees,
-            @coordinates_of_the_day.declination.degrees,
-            @coordinates_of_the_next_day.declination.degrees
-          ],
+          Util::Maths.normalize_angles_for_interpolation(
+            [
+              @coordinates_of_the_previous_day.declination.degrees,
+              @coordinates_of_the_day.declination.degrees,
+              @coordinates_of_the_next_day.declination.degrees
+            ]
+          ),
           @initial_rising + leap_day_portion
         )
       )
@@ -202,11 +210,13 @@ def declination_rising
     def declination_setting
       Angle.from_degrees(
         Util::Maths.interpolate(
-          [
-            @coordinates_of_the_previous_day.declination.degrees,
-            @coordinates_of_the_day.declination.degrees,
-            @coordinates_of_the_next_day.declination.degrees
-          ],
+          Util::Maths.normalize_angles_for_interpolation(
+            [
+              @coordinates_of_the_previous_day.declination.degrees,
+              @coordinates_of_the_day.declination.degrees,
+              @coordinates_of_the_next_day.declination.degrees
+            ]
+          ),
           @initial_setting + leap_day_portion
         )
       )

diff --git a/lib/astronoby/util/maths.rb b/lib/astronoby/util/maths.rb
@@ -29,6 +29,28 @@ def interpolate(values, factor)
             "Only 3 or 5 terms are supported for interpolation"
         end
 
+        # Fixes angles forced to be in range [0, 360] or other angle range, for
+        # interpolation use
+        # @param angles [Array<Integer|Float>] Angles values
+        # @param full_circle [Integer] Full circle value
+        # @return [Array<Interger|Float>] Normalized values
+        def normalize_angles_for_interpolation(angles, full_circle: 360)
+          normalized = angles.dup
+
+          (1...normalized.size).each do |i|
+            prev_angle = normalized[i - 1]
+
+            while normalized[i] - prev_angle > full_circle / 2
+              normalized[i] -= full_circle
+            end
+            while normalized[i] - prev_angle < -full_circle / 2
+              normalized[i] += full_circle
+            end
+          end
+
+          normalized
+        end
+
         private
 
         # @return [Float] Interpolated value

diff --git a/spec/astronoby/bodies/moon_spec.rb b/spec/astronoby/bodies/moon_spec.rb
@@ -445,6 +445,44 @@
       expect(rising_time).to eq Time.utc(2024, 11, 10, 18, 49, 45)
     end
 
+    it "returns moonrise time on 2024-11-12" do
+      time = Time.utc(2024, 11, 12)
+      utc_offset = "-06:00"
+      observer = Astronoby::Observer.new(
+        latitude: Astronoby::Angle.from_degrees(41.87),
+        longitude: Astronoby::Angle.from_degrees(-87.62),
+        utc_offset: utc_offset
+      )
+      moon = described_class.new(time: time)
+      observation_events = moon.observation_events(observer: observer)
+
+      rising_time = observation_events.rising_time
+
+      expect(rising_time.getlocal(utc_offset))
+        .to eq Time.new(2024, 11, 12, 14, 39, 55, utc_offset)
+      # Time from the IMCCE: 2024-11-12T14:41:07-06:00
+      # Time from the Stellarium: 14:40
+    end
+
+    it "returns moonrise time on 2024-11-13" do
+      time = Time.utc(2024, 11, 13)
+      utc_offset = "-06:00"
+      observer = Astronoby::Observer.new(
+        latitude: Astronoby::Angle.from_degrees(41.87),
+        longitude: Astronoby::Angle.from_degrees(-87.62),
+        utc_offset: utc_offset
+      )
+      moon = described_class.new(time: time)
+      observation_events = moon.observation_events(observer: observer)
+
+      rising_time = observation_events.rising_time
+
+      expect(rising_time.getlocal(utc_offset))
+        .to eq Time.new(2024, 11, 13, 15, 4, 20, utc_offset)
+      # Time from the IMCCE: 2024-11-13T15:05:34-06:00
+      # Time from the Stellarium: 15:04
+    end
+
     describe "#rising_azimuth" do
       it "returns the moonrise azimuth on 2024-05-31" do
         time = Time.utc(2024, 5, 31)

diff --git a/spec/astronoby/util/maths_spec.rb b/spec/astronoby/util/maths_spec.rb
@@ -61,4 +61,26 @@
       end
     end
   end
+
+  describe "::normalize_angles_for_interpolation" do
+    [
+      [[10, 20, 30], [10, 20, 30], 360],
+      [[330, 340, 350], [330, 340, 350], 360],
+      [[343, 356, 9], [343, 356, 369], 360],
+      [[355, 2, 12], [355, 362, 372], 360],
+      [[1, 2, 3], [1, 2, 3], 12],
+      [[21, 22, 23], [21, 22, 23], 24],
+      [[22, 23, 2], [22, 23, 26], 24],
+      [[23, 2, 3], [23, 26, 27], 24]
+    ].each do |input, expected_output, full_circle|
+      it "normalizes the angles for interpolation" do
+        normalized = described_class.normalize_angles_for_interpolation(
+          input,
+          full_circle: full_circle
+        )
+
+        expect(normalized).to eq expected_output
+      end
+    end
+  end
 end