Orthographic projection

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This article is about technical drawings. See Orthographic projection (geometry) for linear transformations and Orthographic projection (cartography) for maps. For the language concept, see orthography.

Example of orthographic drawing from a US Patent (1913), showing two views of the same object. Third angle projection is used.

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°. Equivalently, the views may be considered to be obtained by rotating the object about its center through increments of 90°.

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:

[edit] First-angle projection

In first-angle projection, each view of the object is projected in the direction (sense) of sight of the object, onto the interior walls of the box; that is, each view of the object is drawn on the opposite side of the box:

A two-dimensional representation of the object is then created by "unfolding" the box, to view all of the interior walls:

This produces two plan views and four side views.

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