Piwik\UrlHelper::getParameterFromQueryString PHP Method

    public static function getParameterFromQueryString($urlQuery, $parameter)
    {
        $nameToValue = self::getArrayFromQueryString($urlQuery);
        if (isset($nameToValue[$parameter])) {
            return $nameToValue[$parameter];
        }
        return null;
    }

 public function getKeywordPosition()
 {
     if ($this->getReferrerType() == 'search' && strpos($this->getReferrerName(), 'Google') !== false) {
         $url = @parse_url($this->details['referer_url']);
         if (empty($url['query'])) {
             return null;
         }
         $position = UrlHelper::getParameterFromQueryString($url['query'], 'cd');
         if (!empty($position)) {
             return $position;
         }
     }
     return null;
 }