def to_s format = :dms, dp = 0 
      format ||= :dms

      return '-,-' if !lat || !lon

      _lat = GeoUnits::Converter.to_lat lat, format, dp
      _lon = GeoUnits::Converter.to_lon lon, format, dp

      "#{_lat}, #{_lon}"
    end
def to_s format = :dms, dp = 0 
      format ||= :dms

      return '-,-' if !lat || !lon

      _lat = GeoUnits::Converter.to_lat lat, format, dp
      _lon = GeoUnits::Converter.to_lon lon, format, dp

      "#{_lat}, #{_lon}"
    end
Returns a string representation of this point; format and dp as per lat()/lon()

 @param   [String] format: Return value as 'd', 'dm', 'dms'
 @param   [Number] dp: No of decimal places to display (0|2|4)
 @return [String] Comma-separated latitude/longitude