Grating is any frequently spaced collection of essentially identical, similar lengthened elements. Gratings usually consist of a single set of elongated elements, but can consist of two sets, in which case the second set is usually perpendicular to the first. Gratings comes into gratings as bridge decks, gratings as filters, diffraction gratings and gratings as pictures. Grating can also come in 4 feet or 2 feet (61 cm) x 8 feet panels often used for decks on bridges, footbridges and catwalks. Grating can be made of different materials like steel, aluminum, and fiberglass. Gratings are also used extensively in research into visual perception.