Drafting for the Theatre

11. Mechanical Perspective—The Long Way and Some Shortcuts

123 11.1 As Seen by the Human Eye Since a significant amount of scenery is constructed using either true or forced perspective , theatre designers, scenic artists, and set fabricators all need to understand the basic principles of perspective. Forced perspective is a term used when the converging lines do not meet at correctly defined vanishing points (as they do in true perspective). Perspective drawings produce images that in many ways resemble a photograph. Illustrators , interior designers, architects, and set designers all use perspective sketches as visual support for their project proposals. A colored perspective sketch or rendering can show a client precisely how the final product will appear in advance of its actual construction, as viewed from a specific location. Like most of today’s active architectural and product designers, many theatre designers use CAD to produce accurate depictions of their design ideas. Most current CAD applications incorporate color, texture, blending, and lighting choices into their packages, and the possibilities boggle the mind. As helpful as these features are, however, in many cases theatrical designers still need to produce quick pencil and ink sketches that are both faster to produce and in many cases provide more artistic inspiration than a more mechanically produced product. This chapter concentrates on the principles of perspective, which, when properly understood, will enable a drafter to create a clear and quick illustration of a visual image. 11.2 Definitions Figures 11.1 and 11.2 illustrate the principal elements of a perspective drawing. Although this chapter focuses on stage applications, the elements and principles of perspective remain the same regardless whether the drawing is used for theatrical, architectural, interior design , or any other similar purpose. Picture Plane (PP): An imaginary vertical plane of projection Station Point (SP): The position of the observer ’s eye (aka observation point, OP) Horizon Line (HL): The edge view of the horizon plane (horizontal), an imaginary reference usually set at the eye level of the observer Ground Line (GL): The edge view of the horizontal ground plane on which the object being drawn rests Vanishing Point (VP): A point (or points) on the horizon line where all receding lines (width and depth) converge; includes vanishing point center (VPC), vanishing point left (VPL), and vanishing point right (VPR) Measuring Line (ML): A perpendicular line dropped from the picture plane to the ground line, at which location the height (vertical dimension) of an object is true size and can be scaled. Most perspective drawings have multiple measuring lines (not shown), such as ML1, ML2 11.3 Variables within a Perspective Drawing Although there are typical placements for the points and planes previously introduced, each 11. Mechanical Perspective—The Long Way and Some Shortcuts 11.1 Perspective drawing: The cone of vision 124 element location can be varied, resulting in a wide variety of differing visual images. Extreme changes in station point location can result in a significant distortion of the object being drawn, while subtle changes will result in minor but often useful degrees of distortion. Location of the Station Point The station point (SP) is usually located along the center line of the proscenium arch (or set) and at a distance far enough back so that the cone of vision from the observer’s eye to the extreme edges of the proscenium (or set) is approximately 30°. An acceptable range in the angle of the cone of vision is considered to be 30° to 60°. Beyond 60°, the image produced will contain a considerable amount of distortion ; if much less than 30°, the object becomes flat and visually less interesting. The use of 30° is an ideal choice, since the distance from the proscenium to the SP is easily determined using the 30°-60° triangle. Shifting the SP to the left or right of center, will, of course, produce an image quite different (fig. 11.3). A similar effect can be achieved by modifying the angle of the object in relation to the picture plane (fig. 11.4). Location of the Picture Plane The picture plane (PP) is usually placed at the plaster line or a similar datum line near and parallel to the proscenium arch. If the object being drawn is located on the picture plane, it 11.2 The elements of a perspective drawing 11.3 Moving the station point alters the cone of vision 125 is true size and shape. As the object is moved...