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Oblique drawings are three-dimensional representations with a vertical face of the drawn object parallel to the picture plane. Oblique drawings are scaled accurately horizontally and vertically, however, the depicted object's depth or width is skewed on a diagonal axis and scaled, half-scaled or not scaled at all. Thus, there are three types of oblique drawings: the scaled oblique, the cabinet projection and the cavalier projection. All obliques are paraline drawings, where the drawn elements' axes remain parallel, versus a perspective in which the axes converge with representational depth.
The scaled oblique is a paraline drawing that has all axes at the same scale. The drawing is useful for showing the dimensionality of an object, however, the angular relationships are not accurate, except on the forward-facing elevation.
A cabinet projection is an oblique drawing that is scaled one-to-one on its horizontal and vertical axes, however, the diagonal axis showing depth is half-scaled. The cabinet projection received its name from cabinet makers who used this oblique drawing method to depict their furniture. The half-scaled axis provides the illusion of foreshortening, although all axial lines are parallel.
A cavalier projection is an oblique drawing that is scaled one-to-one on its horizontal and vertical axes, however, the diagonal axis showing depth is not scaled. The cavalier projection received its name from the horsemen who would survey fortifications. No scale for the depth axis provides the illusion of perspective while framing the importance of the object's verticality.
Axiometrics are related to oblique drawings, however, they are not oblique. They share the paraline projective construction, but instead of presenting a vertical face to the picture plane, axiometrics present a corner edge to the picture plane. Axiometrics are more appropriate for showing the spatial nature of an object, whereas obliques are more appropriate for showing the vertical nature of the object's faces.
- "Architectural Drawing"; Rendow Yee; 2007
- "Architectural Graphic Standards"; American Institute of Architects; 2007
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