Orthographic projection

Orthographic projection is a means through which a three-dimensional object may be represented in two dimensions. It uses multiple views of the object, from points of view (with infinite perspective[?]) rotated about the object's center through increments of 90 degrees. Equivalently, the views may be considered to be obtained by rotating the object about its center through increments of 90 degrees.

The views are positioned relative to each other according to either of two schemes: first-angle or third-angle projection. In each, the appearances of faces may be thought of as being projected onto planes that form a "box" around the object.

In first-angle projection, each view of the object is projected "through" the object, onto the interior walls of the box. A two-dimensional representation of the object is then created by "unfolding" the box, to view all of the interor walls.

In third-angle projection, each view of the object is projected "outward" from the object, onto the (transparent) exterior walls of the box. A two-dimensional representation of the object is then created by unfolding the box, to view all of the exterior walls.

The term "third-angle" is used because, compared to "first-angle" projection, the directions of projection are rotated through two right angles about the object. First-angle projection is often considered to be less intuitive than third-angle projection.