bug 4.7.16: Error in distance calculation in Item.php

[BN_IT_Support]

Hello.

I started with your distance calculation in Item.php:

      $selectClause .= ', ( 3959 * acos( cos( radians(' . $location['lat'] . ') ) * cos( radians( ' . static::$databasePrefix . 'latitude' . ' ) ) * cos( radians( ' . static::$databasePrefix . 'longitude' . ' ) - radians( ' . $location['lon'] . ' ) ) + sin( radians( ' . $location['lat'] . ' ) ) * sin( radians( ' . static::$databasePrefix . 'latitude' . ') ) ) ) AS distance';
 

I converted this to a PHP calculation (and I believe that I got the conversion correct!)

     $distance = (3959 * acos(cos(deg2rad($lat)) * cos(deg2rad($long)) * cos(deg2rad($event_long) - deg2rad($long)) + sin(deg2rad($lat)) * sin(deg2rad($event_lat))));
 

The problem is that this version of the calculation gave me 'NAN' (Not a Number) for the values that I tested.

After a quick Google for the algorithm I found the 'Haversine formula' and that seems to work OK.

     $distance = 3959 * acos(sin(deg2rad($lat))*sin(deg2rad($event_lat))+cos(deg2rad($lat))*cos(deg2rad($event_lat))*cos(deg2rad($event_long)-deg2rad($long)));
 

I conclude that your calculation in Item.php is incorrect.

John