public function test_bearing()
 {
     // Helsinki-Malmi airport (EFHF)
     $efhf = new midgardmvc_helper_location_spot(60.254558, 25.042828);
     // Helsinki-Vantaa airport (EFHK)
     $efhk = new midgardmvc_helper_location_spot(60.317222, 24.963333);
     // Helsinki-Vantaa is in north of Helsinki-Malmi
     $bearing = $efhf->bearing_to($efhk);
     $this->assertEquals($bearing, 329);
     // Helsinki-Malmi is in south of Helsinki-Vantaa
     $bearing = $efhk->bearing_to($efhf);
     $this->assertEquals($bearing, 149);
     // Test bearing within same location
     $bearing = $efhf->bearing_to($efhf);
     $this->assertEquals($bearing, null);
     // Midgard airport (FYMG)
     $fymg = new midgardmvc_helper_location_spot(-22.083332, 17.366667);
     $bearing = $efhf->bearing_to($fymg);
     $this->assertEquals($bearing, 187);
 }