An oblique drawing is a simple form of three-dimensional (3D) drawing that is often created for drafting or engineering. Such a drawing usually consists of an object in which the front of the object is drawn flat, with the height and width of the object drawn the proper lengths. The object is then given depth through sides drawn at an angle to create the sense of the object being three-dimensional; this is often at a 45° angle and the sides can be foreshortened. An oblique drawing will typically be one of three types: normal, cabinet, or cavalier.
To create an oblique drawing, an engineer or designer will usually begin with a “three-view drawing.” This consists of a single object rendered in three distinct views: from the front, the side, and the top. The front drawing is usually created first to establish the height and width of the object. The vertical lines of the front view can then be extended upward on the paper, the depth of the object is added to these and this creates the top view. Horizontal lines from the front view can then be extended to the side of the front view, the proper depth is used once again, and the side view is thereby created.
With a three-view drawing, a designer or engineer can then easily create an oblique drawing. This is done by using the height and width from the front view, and keeping them the same size. The depth of the top and side views can then be used to add depth to the oblique drawing and create the sense of 3D in the image. While any angle could potentially be chosen to create the depth lines, a 45° angle is often chosen for the easily visible nature of lines at that angle.
The length of the lines used to add depth to the object determines the type of oblique drawing being created. Normal oblique drawings use depth lines that are only three-fourths the length of the depth established by the three-view drawing. Cabinet drawings use lines only half the length of the original depth lines to create the oblique object.
In either of these types, the object will appear foreshortened and seem closer to how it might actually appear in 3D space. A cavalier oblique drawing, on the other hand, uses depth lines that are the same length as the top and side views in the three-view drawing. Though this retains the sizes provided in the three-view image, the perspective created by this type of oblique is much more exaggerated.
