[Figures 3-6] Perspective sketches (top left) are required to nail down the concept, but modeling from them is difficult. Orthographic views (top right and bottom) are side views of the object shown without perspective distortion.

2D Reference Material
A 2D image can be a sketch or a photograph that is scanned into the computer and used inside the modeling program as a background for the modeling window, called an image plane. Gathering reference material, especially 2D images, is a requirement for most modeling projects. In cases where a 3D reference is available, 2D images can be used as image planes in addition to the 3D reference data.

Perspective 2D Reference
When creating an original concept on the computer, a modeler usually begins with a 3D sketch, or a perspective sketch (Figure 3). This perspective image can also be a photograph in cases where the model will not be an original design. Some modelers will choose to model from a perspective image in the perspective window, but the more accepted practice is to use the orthographic windows. This way the modeler can ensure that details seen from one view line up with details seen in another view.

Whereas a perspective sketch or photograph may be adequate at the earlier stages of design development, the 2D orthographic projection — a plan and two elevations — is the conventional way of communicating the form and geometry of the product from design to production. In order to understand ortho-graphic images, you must first understand the concept of orthographic projection.

Orthographic Drawings
Orthographic projection is a way of viewing objects that puts the object in a theoretical box. The surfaces of this box represent the top, bottom, back, front, left and right sides of the object. If the person viewing the object were to stand so the view was perfectly perpendicular to one of the surfaces of this theoretical box, this would be an orthographic view. The modeling views in most modeling windows enable the modeler to work in this orthographic mode, generally from the top, front and right sides. In cases where the modeler is not creating an original design, photographs taken of the object in orthographic views are suitable images for constructing a 3D model. Orthographic views (Figures 4 through 6) also enable the modeler to work in views that are not distorted by the perspective camera, allowing for the accurate interpretation of the drawings onto the actual model.

The method of orthographic projection is to “float” the designed object inside this imaginary box (Figure 7). Imagine the box as a window that you look through — the silhouette or projection of the designed object onto the top horizontal window is called the plan; the projection of the same object onto the front vertical window is the front elevation; and onto an adjacent side vertical window is an end or side elevation. Now imagine the box to be hinged. The horizontal plan is swung up through 90 degrees and the end elevation is also swung around through 90 degrees so that all three projections now lie on the same plane.