What Is the Meaning of Orthographic Drawing?

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What Is the Meaning of Orthographic Drawing?
A house drawn in an orthographic view. (maison bretonne image by Oliv from Fotolia.com)

"Orthographic drawing" refers to a 2-D representation of an object in a view that shows only one side at a time. Most orthographic drawings occur in multi-drawing sets in order to depict each side, top and bottom view. Professions in design and construction use these types of drawings to inform the viewer of layout, size and shape. House floor plans illustrate a common type of orthographic drawing.

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Types

Orthographic drawings include elevations, plans and sections, which are drawn in such a way that the view frame (also known as a picture plane) is parallel to the object. The viewer sees exactly one side of the object in an orthographic drawing. Elevations depict a front, back or side face of the object. A plan illustrates the object from a top orientation looking downward, like an aerial view. Plans may illustrate different qualities of the object depending upon the placement of the view frame above or within an object. For example, a house would have different plans depending on whether viewing the basement, first floor or second floor. A section drawing creates a cross-section of an object, illustrating what would appear at the location of the cut if the viewer could see inside the object.

Advantages

Orthographic drawings, when drawn to scale, can be used to determine accurate dimensions. According to Francis Ching, "Every feature or element which is parallel to the picture plane [or view frame] remains true in size, shape, and configuration." For example, a shed drawn next to a house in an orthographic drawing would represent the real life proportions of the building faces with respect to one another, the actual distance between the buildings, and the shape of the visible building faces.

Limitations

Orthographic drawings do not show depth or realistic views. A single-view orthographic drawing represents every object as having only two dimensions. However, by assembling two or more drawings with overlapping features or by using line weight and shading, orthographic drawings can depict the depth of objects. Additionally, the human eye views the world in perspective, not in the two dimensions of orthographic drawings. Ching states, "Orthographic views are abstract in the sense that they do not match optical reality." Curvilinear shapes and diagonals that exist in three dimensions represent an example of distortion created by orthographic drawing. These shapes appear distorted and shortened because their entirety does not sit parallel to the view frame.

Uses

Design and construction industries often use orthographic drawings to communicate dimensions and shape. Real estate agents and realtors commonly use floor plans to show prospective buyers the layout and square footage of buildings. Engineers and architects use various plans, sections and elevations to depict designs and detail constructions of objects and buildings. For example, a section might show the cross-section of specific walls to illustrate the placement of heating and plumbing elements. Similarly, a reflected ceiling plan show a living room's vaulted ceiling or a multi-floor opening in an atrium. Additionally, an elevation may depict a custom kitchen cabinet design or show location and height of windows on a wall. Professionals use orthographic drawings to communicate their design and turn it into actual constructed elements.

Related Drawings

Axonometric drawings are often also classified as orthographic drawings despite showing an object in three dimensions. Any edge parallel to the viewer is drawn true to scale in an axonometric drawing. The other angles of the object, however, are not orthographic and subsequently distorted in order to show the three dimensions of the object. Similarly, the related phrase "orthographic projection" refers to the detailed process of constructing orthographic drawing sets by projecting related information from one drawing to another. For example, horizontal lines projected from one elevation of a flat-roof shed depict the height dimension of walls on all subsequent orthographic exterior elevations. One piece of information, such as the example shed wall height, is duplicated from one view to another quickly and efficiently through orthographic projection.

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