For many years architects and engineers have utilized a system known as orthographic projection to accurately represent three-dimensional objects graphically on paper. In recent years the term "multiview
Figure 5.1A An example of a simple drawing of objects that essentially requires only two views to read.
FRONT VIEW SIDE VIEW
Figure 5.2 A drawing of an object requiring three views to interpret correctly.
drawing" has come into general use, indicating that more than one view is used to illustrate an object, but the terms are essentially synonymous. "Orthographic" comes from the Greek word for "straight writing (or drawing)." Orthographic projection shows the object as it looks from the front, right, left, top, bottom, or back, and different views are typically positioned relative to each other according to the rules of either first-angle or third-angle projection. Ortho views depict the exact shape of an object seen from one side at a time as you are looking perpendicularly to it without showing any depth.
A single view of an object is rarely adequate to show all necessary features. Figure 5.3 is an example of orthographic projection showing the six principal views used by architects and engineers in construction and industrial drawings.
Common types of orthographic drawings include plans, elevations, and sections. The most obvious attribute of orthographic drawing is its constant scale—that is, all parts of the drawing are represented without foreshortening or distortion, retaining their true size, shape, and proportion. Thus, in an orthographic drawing, a window shown to be 8 feet wide by 4 feet high will always be drawn at this size, no matter how far it is from our viewpoint (Figure 5.4).
Plans are really orthographic views of an object as seen directly from above. Floor plans are the most common form of plan; they delineate the layout of a building. A floor plan is represented by a horizontal section taken through the building or portion of a building just above the windowsill level. In addition to the arrangement of rooms and spaces, floor plans need to show the location of various architectural elements such as stairs, doors, and windows and details such as wall and partition thickness. Generally, the greater the scale of a drawing, the more detail that it is expected to contain (Figure 5.5). Thus, a drawing at a scale of 1/4" = 1'0" will typically contain more information and show more detail than a drawing at a 1/8" = 1'0" scale. Likewise, a scale of 1:2 is greater than that of 1/4 inch = 1 foot, 0 inches. Other types of plans used in building construction may include site plans, which typically show the layout of a site; foundation plans. which show the building structure; and reflected ceiling plans, which are normally used to locate light fixtures and design features.
Two important rules that must be adhered to in orthographic drawing are the placement and alignment of views, depending on the type of projection to be used. These rules are discussed below. In addition, projection lines between the views must be aligned horizontally and vertically.
Orthographic (multiview) projection is a generally accepted convention for representing three-dimensional (3D) objects using multiple dimensions (2D) of the front, top, bottom, back, and sides of the object. In practice, the minimum number of views possible is used to describe all the details of the object. Usually, a front view, top, and single side view are sufficient and are oriented on the paper according to accepted convention. Figure 5.6 represents a multiview projection for a simple house. The projection clearly shows that it is a form of parallel projection, and the view direction is orthogonal to the projection plane. Isometric projection attempts to represent 3D objects using a single view. Instead of the observer viewing the object perpendicular to it, the object is rotated both horizontally and vertically relative to the observer. There are rules and conventions to guide the creation of both types of projections. Additionally, either of them can be supplemented with various types of dimensions.
Was this article helpful?