public function formatDecimal( int $precision = 8 ) : string
   {

      $returnValue = '';

      if ( ! $this->isValid() )
      {
         return $returnValue;
      }

      $returnValue .= $this->Latitude->formatDecimal( $precision )
                      .  ', '
                      .  $this->Longitude->formatDecimal( $precision );

      return $returnValue;

   }