Merge pull request #27 from WimDeMeester/master

Calculate angular separation.
DeepskyLog · Jun 15, 2020 · cb3d29f · cb3d29f
2 parents 9b3149e + c03e56b
commit cb3d29f
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diff --git a/changelog.md b/changelog.md
@@ -2,6 +2,12 @@
 
 All notable changes to `laravel-astronomy-library` will be documented in this file.
 
+## Version 4.4
+
+### Added
+
+- Added methods to calculate the angular separation between two objects.
+
 ## Version 4.3
 
 ### Added

diff --git a/composer.lock b/composer.lock
diff --git a/readme.md b/readme.md
@@ -194,6 +194,7 @@ $horizontal = $coords->convertToHorizontal($geo_coords, $siderial_time);
 $galactic = $coords->convertToGalactic();
 $parallacticAngle = $coords->getParallacticAngle($geo_coords, $siderial_time);
 $hour_angle = $coords->getHourAngle($siderial_time);
+$angular_separation = $coords->angularSeparation($coords2)->getCoordinate();
 ```
 
 ### Coordinate methods on ecliptical coordinates

diff --git a/src/deepskylog/AstronomyLibrary/Coordinates/EquatorialCoordinates.php b/src/deepskylog/AstronomyLibrary/Coordinates/EquatorialCoordinates.php
@@ -105,7 +105,7 @@ public function printDeclination(): string
      */
     public function printRA(): string
     {
-        return $this->getRA()->convertToHours;
+        return $this->getRA()->convertToHours();
     }
 
     /**
@@ -278,4 +278,53 @@ public function getHourAngle(Carbon $siderial_time): float
 
         return ($sid - $this->getRA()->getCoordinate()) * 15.0;
     }
+
+    /**
+     * Returns the angular separation between these coordinates and other
+     * equatorial coordinates.
+     *
+     * @param EquatorialCoordinates $coords2 the coordinates of the second object
+     *
+     * @return Coordinate The angular separation between the two objects
+     */
+    public function angularSeparation(
+        self $coords2
+    ): Coordinate {
+        $d = rad2deg(
+            acos(
+                sin(deg2rad($this->getDeclination()->getCoordinate())) *
+                sin(deg2rad($coords2->getDeclination()->getCoordinate()))
+                + cos(deg2rad($this->getDeclination()->getCoordinate())) *
+                cos(deg2rad($coords2->getDeclination()->getCoordinate())) *
+                cos(
+                    deg2rad(
+                        $this->getRA()->getCoordinate() * 15.0
+                        - $coords2->getRA()->getCoordinate() * 15.0
+                    )
+                )
+            )
+        );
+
+        if ($d < 0.16) {
+            $d = sqrt(
+                (
+                    $this->getRA()->getCoordinate() * 15.0
+                    - $coords2->getRA()->getCoordinate() * 15.0
+                ) * cos(
+                    deg2rad(
+                        (
+                            $this->getDeclination()->getCoordinate()
+                            + $coords2->getDeclination()->getCoordinate()
+                        ) / 2
+                    )
+                ) ** 2 +
+                (
+                    $this->getDeclination()->getCoordinate()
+                    - $coords2->getDeclination()->getCoordinate()
+                )
+            );
+        }
+
+        return new Coordinate($d);
+    }
 }
diff --git a/tests/Unit/EquatorialCoordinatesTest.php b/tests/Unit/EquatorialCoordinatesTest.php
@@ -188,4 +188,32 @@ public function testParallacticAngle()
             $equa->getParallacticAngle($geo, $astrolib->getApparentSiderialTime())
         );
     }
+
+    /**
+     * Test angular separation.
+     *
+     * @return None
+     */
+    public function testAngularSeparation()
+    {
+        // Arcturus and Spica
+        $equa1 = new EquatorialCoordinates(14.2610277778, 19.1825);
+        $equa2 = new EquatorialCoordinates(13.4198888, -11.1614);
+
+        $this->assertEqualsWithDelta(
+            $equa1->angularSeparation($equa2)->getCoordinate(),
+            32.7930,
+            0.0001
+        );
+
+        // Aldebaran and Antares
+        $equa1 = new EquatorialCoordinates(4.598677519444444, 16.509302361111111);
+        $equa2 = new EquatorialCoordinates(16.490127694444444, -26.432002611111111);
+
+        $this->assertEqualsWithDelta(
+            $equa1->angularSeparation($equa2)->getCoordinate(),
+            169.9627,
+            0.0001
+        );
+    }
 }