Grating

A grating is any regularly spaced collection of essentially identical, parallel, elongated 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 (as illustrated). When the two sets are perpendicular, this is also known as a wikt:grid (as in grid paper) or a mesh. A grating covering a drain (as illustrated) can be a collection of iron bars (the identical, elongated elements) held together (to ensure the bars are parallel and regularly spaced) by a lighter iron frame. Gratings over drains and air vents are used as filters, to block movement of large solids (e.g. people) and to allow movement of liquids. A register is a type of grating used in heating, ventilation, and air conditioning, which transmits air, while stopping solid objects. File:Vindobona Hoher Markt-71.JPG|Grating - drain cover, [[ancient Roman architecture]] at [[Vindobona]], [[Austria]]. File:Montreal Sewer Cover.jpg|Sewer grating ([[manhole cover]]) that can be driven on despite letting water pass through File:Tree grating, Washington, D. C. (3678939694).jpg|[[Tree grate|Tree grating]] that can be walked on despite letting water pass through Anti-slip grating Grating can also come in panels that are often used for decks on bridges, footbridges and catwalks. Grating can be made of materials such as steel, aluminum, fiberglass. Fiberglass grating is also known as FRP grating. They are used to optimize bending stiffness while minimizing weight. File:Grating at the historic John Street Roundhouse, Toronto.jpg|Close up view of [[anti-slip grating]] File:Puente rejilla.jpg|Bridge showing deck grating driving surface File:Stahlbau mit Gitterrosten.JPG|Walkway gratings at a power plant As optical elements, optical gratings are images having the characteristic pattern of alternating, parallel lines. The lines alternate between high and low reflectance (black-white gratings) or high and low transmittance (transparent-opaque gratings).