class FilterForm extends AdvancedSearchForm {
…
   function getQuery($searchParams, $sort = false, $limit = false, $existingQuery = null) {
      …
      
      // check if location fields are set and modify query
      if (isset($searchParams['Location__Lat']) || isset($searchParams['Location__Lng'])) {
         $query = $this->extendLocationSQL($searchParams, $query, $context);
      }
      
      foreach ($searchParamArray as $key => $data) {
         $key = str_replace('__', '.', $key);
         
         if ($filter = $context->getFilter($key)) {
         
            if (isset($data['filter'])) {
               // remove old
               $context->removeFilterByName($key);

               // create new
               $filter = new $data['filter']($key);
               $context->addFilter($filter);
            }
            
            $filter->setModel($this->stat('classToSearch'));
            $filter->setValue($data['value']);
            
            if (!$filter->isEmpty()) {
               $filter->apply($query);
            }
         }
      }
      
      $query->connective = $context->connective;
      $query->distinct = true;

      $model->extend('augmentSQL', $query);
      
      return $query;
   }

   /**
    * modify the current search-query to find entries by distance
    *
    */
   private function extendLocationSQL($searchParams, $query, $context) {
      
      if (isset($searchParams['Location__Distance'])) {
         
         $lat = $searchParams['Location__Lat'];
         $lat = isset($lat['value']) ? (float) $lat['value'] : false;
         
         $lng = $searchParams['Location__Lng'];
         $lng = isset($lng['value']) ? (float) $lng['value'] : false;
         
         $distance = $searchParams['Location__Distance'];
         $distance = isset($distance['value']) ? (float) $distance['value'] : false;
         
         // remove default Location Filters
         $context->removeFilterByName('Location.Lat');
         $context->removeFilterByName('Location.Lng');
      
         if (!$distance || !$lat || !$lng)
            return $query;

         if (!$query->isJoinedTo('Location')) {
            $query->leftJoin('Location', '"Location"."ID" = "Record"."LocationID"');
         }
         
         $query->select['LocationDistance'] = '(3959 * acos(cos(radians(' . $lat . ')) * cos(radians("Location"."Lat")) * cos( radians("Location"."Lng") - radians(' . $lng . ')) + sin(radians(' . $lat . ')) * sin(radians("Location"."Lat")))) AS LocationDistance';
         $query->having[] = 'LocationDistance < ' . $distance;
      }
   
      return $query;
   }
}