Added support for the Haversine formula.

README.md

@@ -16,7 +16,7 @@ When using [Composer](https://getcomposer.org) you can always load in the latest
 ```bash
 {
     "require": {
-        "ldebrouwer/distance": "dev-master"
+        "ldebrouwer/distance": "~0.2"
     }
 }
 ```
@@ -27,6 +27,5 @@ Check it out [on Packagist](https://packagist.org/packages/ldebrouwer/distance).
 This is still on the to-do list. The code is pretty well documented though and should autocomplete in most IDEs.
 
 ## Still to come
-- Haversine formula support.
 - Expanded unit support.
 - Documentation.

src/Distance.php

@@ -47,6 +47,7 @@ class Distance
      * @param float $longitudeB The longitude for point B.
      *
      * @uses betweenVincenty
+     * @uses betweenHaversine
      * @throws Exception
      * @return float
      */
@@ -87,6 +88,29 @@ private function betweenVincenty($latitudeA, $longitudeA, $latitudeB, $longitude
         return floor($angle * 6371000);
     }
 
+    /**
+     * Method that returns the distance between two GPS locations in meters according to the Haversine formula.
+     *
+     * @param float $latitudeA The latitude for point A.
+     * @param float $longitudeA The longitude for point A.
+     * @param float $latitudeB The latitude for point B.
+     * @param float $longitudeB The longitude for point B.
+     *
+     * @return float
+     */
+    private function betweenHaversine($latitudeA, $longitudeA, $latitudeB, $longitudeB)
+    {
+        $latitudeA = deg2rad($latitudeA);
+        $longitudeA = deg2rad($longitudeA);
+        $latitudeB = deg2rad($latitudeB);
+        $longitudeB = deg2rad($longitudeB);
+        $latDelta = $latitudeB - $latitudeA;
+        $longDelta = $longitudeB - $longitudeA;
+        $angle = 2 * asin(sqrt(pow(sin($latDelta / 2), 2) + cos($latitudeA) * cos($latitudeB) * pow(sin($longDelta / 2), 2)));
+
+        return floor($angle * 6371000);
+    }
+
     /**
      * @param $distance
      * @return mixed
@@ -115,7 +139,7 @@ public function getFormula()
      */
     public function setFormula($formula)
     {
-        if (!in_array($formula, ['vincenty'])) {
+        if (!in_array($formula, ['vincenty', 'haversine'])) {
             throw new Exception('You have tried to set an invalid distance formula.');
         }
 

tests/DistanceTest.php

@@ -67,9 +67,9 @@ public function testInvalidParams()
     }
 
     /**
-     * Test the retrieval of the distance between the Apple and Google campuses.
+     * Test the retrieval of the distance between the Apple and Google campuses using the Vincenty formula.
      */
-    public function testDistanceBetweenAppleAndGoogle()
+    public function testDistanceBetweenAppleAndGoogleUsingVincenty()
     {
         $distance = new Distance();
         $distance->setUnit('m');
@@ -97,4 +97,36 @@ public function testDistanceBetweenAppleAndGoogle()
 
         $this->assertEquals(439527.5586068, $distance->between(37.331741, -122.030333, 37.422546, -122.084250));
     }
+
+    /**
+     * Test the retrieval of the distance between the Apple and Google campuses using the Haversine formula.
+     */
+    public function testDistanceBetweenAppleAndGoogleUsingHaversine()
+    {
+        $distance = new Distance();
+        $distance->setUnit('m');
+        $distance->setFormula('haversine');
+
+        $this->assertEquals(11164, $distance->between(37.331741, -122.030333, 37.422546, -122.084250));
+
+        $distance->setUnit('km');
+
+        $this->assertEquals(11.164, $distance->between(37.331741, -122.030333, 37.422546, -122.084250));
+
+        $distance->setUnit('mi');
+
+        $this->assertEquals(6.936987987488, $distance->between(37.331741, -122.030333, 37.422546, -122.084250));
+
+        $distance->setUnit('cm');
+
+        $this->assertEquals(1116400, $distance->between(37.331741, -122.030333, 37.422546, -122.084250));
+
+        $distance->setUnit('ft');
+
+        $this->assertEquals(36627.2966436, $distance->between(37.331741, -122.030333, 37.422546, -122.084250));
+
+        $distance->setUnit('in');
+
+        $this->assertEquals(439527.5586068, $distance->between(37.331741, -122.030333, 37.422546, -122.084250));
+    }
 }