The orthogonal projection (or view) is, by definition, a radiographic projection obtained 90 degrees to the original view. It forms the basic requirements of a 'radiographic series', that being 'two orthogonal projections of the region of interest'
Cases can appear normal in one projection; abnormal in the next (case 5) consequently plain radiographic imaging in the acute setting is seldom a single projection, often comprising of two or more angles of the same region. Orthogonal projections in the acute setting are necessary to convey the three-dimensional nature of the anatomy in question.
One should always strive to perform (as radiographers) or request (as referrers) orthogonal views. When orthogonal views are not possible, views taken at an alternative angle to the first is still more beneficial than no second view at all.
Foreign body imaging
Plain radiographic investigations of foreign bodies often require orthogonal projections to better understand the position in relation to anatomical structures. The orthogonal projections of foreign bodies are often known as the 'en face' projection, whereby the radiographer performs imaging orthogonal to the foreign body rather than anatomical structures.