Orthographic Projections Derived from CAD
Orthographic projections derived from Computer-Aided Design (CAD) are two-dimensional representations of a three-dimensional digital model, generated using parallel projection techniques to accurately convey an object's dimensions, geometry, and features. In modern engineering and manufacturing workflows, these 2D drawings bridge the gap between digital solid models and physical fabrication by standardizing how complex parts are viewed and dimensioned according to established drafting standards.
The Principle of Orthographic Projection in CAD
In technical drafting, an orthographic projection flattens a 3D object onto a series of mutually perpendicular 2D planes: the horizontal, frontal, and profile planes. In traditional manual drafting, draftspersons constructed these views line-by-line using drafting boards, T-squares, and geometric construction methods.
When derived from CAD, the process utilizes the underlying mathematical definition of a 3D solid or surface model. The CAD software calculates the boundary edges, intersections, and silhouettes of the 3D model along defined viewing vectors, projecting those lines onto a virtual 2D drawing sheet. Because the 3D model acts as the single source of truth, the projected 2D views are mathematically precise and eliminate manual projection errors.
Standard Views Generated from 3D Models
A complete set of orthographic projections derived from CAD typically includes:
- Primary (Principal) Views: These correspond to standard orthogonal viewpoints: Front, Top (Plan), Right Side, Left Side, Rear, and Bottom. Most engineering drawings employ a multi-view configuration showing three primary views (typically Front, Top, and Right Side).
- Section Views: CAD allows internal features to be revealed by cutting through the 3D model along a designated cutting plane. The software automatically applies hatching to the sliced solid regions.
- Auxiliary Views: When an object has an inclined or slanted surface, standard primary views foreshorten that feature. An auxiliary view projects perpendicular to the inclined face to display its true shape and size.
- Detail Views: CAD enables magnified circular or rectangular projections of intricate features to facilitate clear dimensioning.
Projection Systems: First-Angle vs. Third-Angle
CAD packages can instantly configure orthographic projections based on regional technical standards:
- Third-Angle Projection: Primarily used in North America (ASME standards), this convention positions the projection plane between the viewer and the object. The top view is placed directly above the front view, and the right-side view is to the right of the front view.
- First-Angle Projection: Predominantly used in Europe and internationally (ISO standards), the object is positioned between the viewer and the projection plane. Consequently, the view from the top is projected below the front view, and the view from the left is placed to the right.
CAD drafting environments manage these conventions automatically via drawing sheet settings, applying the corresponding projection symbol in the title block.
Associativity and Modern Drafting Workflows
The definitive characteristic of CAD-derived orthographic projections is bi-directional associativity. When dimensions, features, or geometries are modified in the 3D CAD part or assembly, the derived orthographic drawing views update automatically, along with their associated dimensions, annotations, and centerlines.
This derived drafting method maintains traditional engineering drawing conventions—such as visible object lines, hidden dashed lines, and phantom lines—while significantly reducing drawing production time and ensuring strict geometric fidelity between design and manufacturing documentation.