Egy field értékéből egy másik field kreálása - de hogyan kell ezt tisztességesen csinálni?

/**
 * @see http://previousnext.com.au/blog/creating-custom-display-suite-fields-or-how-i-learned-stop-worrying-and-use-hookdsfieldsinfo
 */
 
/**
 * Implements hook_ds_fields_info().
 * @see http://drupalcontrib.org/api/drupal/contributions!ds!ds.api.php/function/hook_ds_fields_info/7
 */
function MYMODULE_ds_fields_info($entity_type) {
  $fields = array();
 
  $fields['node']['mytestbundle_gps'] = array(
    // title: title of the field
    'title' => t('GPS'),
    // type: type of field
    // - DS_FIELD_TYPE_FUNCTION   : calls a custom function.    
    'field_type' => DS_FIELD_TYPE_FUNCTION,
    // ui_limit : only used for the manage display screen so
    // you can limit fields to show based on bundles or view modes
    // the values are always in the form of $bundle|$view_mode
    // You may use * to select all.
    // Make sure you use the machine name.     
    'ui_limit' => array('mytestbundle|*'),   
    // function: only for DS_FIELD_TYPE_FUNCTION. 
    'function' => 'MYMODULE_mytestbundle_ds_field_gps',
  );  
 
  if (isset($fields[$entity_type])) {
    return array($entity_type => $fields[$entity_type]);
  }
  return array();
} 
 
/**
 * Generate GPS coordinates as a DS field
 * Example: 46° 2' 27.24" N 18° 40' 37.2" E
 */
function MYMODULE_mytestbundle_ds_field_gps($field, $title = NULL){
  $output = '';
 
  if(isset($field['entity']->field_teststuff_on_the_map['und'][0])){
    $on_the_map_getlocations_field_data = $field['entity']->field_teststuff_on_the_map['und'][0];
 
    if(isset($on_the_map_getlocations_field_data['latitude']) && isset($on_the_map_getlocations_field_data['latitude'])){
      $output .= theme('getlocations_latitude_dms', $on_the_map_getlocations_field_data);
      $output .=  ' ';
      $output .= theme('getlocations_longitude_dms', $on_the_map_getlocations_field_data);
    }  
  }  
 
  return $output;
}