Orthographic projection

Orthographic projection is a means of representing a three-dimensional object in two dimensions. It uses multiple views of the object, from points of view 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 views may be thought of as being projected onto planes that form a transparent "box" around the object:

Table of contents

1 First-angle projection
2 Third-angle projection
3 Additional information

First-angle projection

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 interior walls:

Third-angle projection

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.

Additional information

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. Second-angle and fourth-angle projection also are defined, but do not result in useful images.

Third-angle projection is often considered to be more intuitive than first-angle projection.