Merge pull request phayes#92 from mprins/adjacent-geohash

Add adjacent geohash function
Michael-Abebe · Nov 30, 2014 · d5b508a · d5b508a
2 parents 478a1a0 + df36b7f
commit d5b508a
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diff --git a/lib/adapters/GeoHash.class.php b/lib/adapters/GeoHash.class.php
@@ -7,8 +7,64 @@
  *
  */
 class GeoHash extends GeoAdapter{
+
+  /**
+   * base32 encoding character map.
+   */
   private $table = "0123456789bcdefghjkmnpqrstuvwxyz";
 
+  /**
+   * array of neighbouring hash character maps.
+   */
+  private $neighbours = array (
+      // north
+      'top' => array (
+          'even' => 'p0r21436x8zb9dcf5h7kjnmqesgutwvy',
+          'odd' => 'bc01fg45238967deuvhjyznpkmstqrwx'
+      ),
+      // east
+      'right' => array (
+          'even' => 'bc01fg45238967deuvhjyznpkmstqrwx',
+          'odd' => 'p0r21436x8zb9dcf5h7kjnmqesgutwvy'
+      ),
+      // west
+      'left' => array (
+          'even' => '238967debc01fg45kmstqrwxuvhjyznp',
+          'odd' => '14365h7k9dcfesgujnmqp0r2twvyx8zb'
+      ),
+      // south
+      'bottom' => array (
+          'even' => '14365h7k9dcfesgujnmqp0r2twvyx8zb',
+          'odd' => '238967debc01fg45kmstqrwxuvhjyznp'
+      )
+  );
+
+  /**
+   * array of bordering hash character maps.
+   */
+  private $borders = array (
+      // north
+      'top' => array (
+          'even' => 'prxz',
+          'odd' => 'bcfguvyz'
+      ),
+      // east
+      'right' => array (
+          'even' => 'bcfguvyz',
+          'odd' => 'prxz'
+      ),
+      // west
+      'left' => array (
+          'even' => '0145hjnp',
+          'odd' => '028b'
+      ),
+      // south
+      'bottom' => array (
+          'even' => '028b',
+          'odd' => '0145hjnp'
+      )
+  );
+
   /**
    * Convert the geohash to a Point. The point is 2-dimensional.
    * @return Point the converted geohash
@@ -163,4 +219,31 @@ private function decode($hash){
     $ll['medlon'] = round(($minlon+$maxlon)/2, max(1, -round(log10($lonE)))-1);
     return $ll;
   }
+
+  /**
+   * Calculates the adjacent geohash of the geohash in the specified direction.
+   * This algorithm is available in various ports that seem to point back to
+   * geohash-js by David Troy under MIT notice.
+   *
+   *
+   * @see https://github.com/davetroy/geohash-js
+   * @see https://github.com/lyokato/objc-geohash
+   * @see https://github.com/lyokato/libgeohash
+   * @see https://github.com/masuidrive/pr_geohash
+   * @see https://github.com/sunng87/node-geohash
+   * @see https://github.com/davidmoten/geo
+   *
+   * @param string $hash the geohash (lowercase)
+   * @param string $direction the direction of the neighbor (top, bottom, left or right)
+   * @return string the geohash of the adjacent cell
+   */
+  public function adjacent($hash, $direction){
+    $last = substr($hash, -1);
+    $type = (strlen($hash) % 2)? 'odd': 'even';
+    $base = substr($hash, 0, strlen($hash) - 1);
+    if(strpos(($this->borders[$direction][$type]), $last) !== false){
+        $base = $this->adjacent($base, $direction);
+    }
+    return $base.$this->table[strpos($this->neighbours[$direction][$type], $last)];
+  }
 }
diff --git a/tests/tests/geohashTest.php b/tests/tests/geohashTest.php
@@ -0,0 +1,20 @@
+<?php
+require_once ('../geoPHP.inc');
+
+class GeoHashTest extends PHPUnit_Framework_TestCase {
+
+  function setUp() {
+  }
+
+  /**
+   * test cases for adjacent geohashes.
+   */
+  function testAdjacent() {
+    $geohash = new Geohash();
+    $this->assertEquals ( 'xne', $geohash->adjacent ( 'xn7', 'top' ), 'Did not find correct top adjacent geohash for xn7' );
+    $this->assertEquals ( 'xnk', $geohash->adjacent ( 'xn7', 'right' ), 'Did not find correct right adjacent geohash for xn7' );
+    $this->assertEquals ( 'xn5', $geohash->adjacent ( 'xn7', 'bottom' ), 'Did not find correct bottom adjacent geohash for xn7' );
+    $this->assertEquals ( 'xn6', $geohash->adjacent ( 'xn7', 'left' ), 'Did not find correct left adjacent geohash for xn7' );
+    $this->assertEquals ( 'xnd', $geohash->adjacent ( $geohash->adjacent ( 'xn7', 'left' ), 'top' ), 'Did not find correct top-left adjacent geohash for xn7' );
+  }
+}