| Attitude Parameters ñ The combination of the viewing distance to the object, and its angular rotation in azimuth, elevation, roll, and offsets that produces a particular viewing aspect. Also, see Fixed Parameters, Parameters, and Variable Parameters. - Azimuth ñ An angular measurement used to orient the object to the desired viewing aspect by rotating it about the vertical (Y) axis of the picture plane. Also, see Elevation, Roll, and Rotation.
 Auxiliary View ñ When the objectís plan view is positioned obliquely to the edges of the Horizontal plane, its side and front views are projected onto the profile and/or frontal planes as Auxiliary views.
 Central Visual Ray (CVR) ñ The central line of sight in the cone of vision. It extends from the eye position to the center of vision on the picture plane. No matter the direction of sight, CVR has a constant perpendicular relationship with the picture plane.
- Center of Vision (CV) ñ The point on the picture plane where the eyelevel line, the central vertical line, and the central visual ray intersect.
 Cone of Vision (CoV) ñ The cone-shaped field of vision, normally about 50†, that extends from the eye to the world beyond. The central visual ray is the centerline of the cone. If the cone extends beyond 30† in a perspective drawing, the extremities of the image tend to become distorted. Whether looking up, down or sidewise, CVR is always parallel to the line of sight.
Elevation ñ An angular measurement used to orient the object to the desired viewing aspect by rotating it about the horizontal (X) axis of the picture plane. Also, see: Azimuth, Roll, and Rotation.
- Eye Position (EP) ñ The location of the observer's eye relative to the picture plane. It's at the same distance above the ground as the horizon. Also, see Picture Plane Environment.
- Fixed Parameters ñ The set of parameters ñ Distance, Azimuth, Elevation, Roll, x-offset, y-offset, z-offset, and Size ñ that fix the viewing aspect (attitude) of the object in a specific exercise. Also, see Attitude Parameters, Parameter, and Variable Parameters.
-
- Horizon Line ñ A trace of the horizon plane on the picture plane. It also serves as the vanishing line. Also, see Picture Plane Environment, and Trace.
Horizontal Plane ñ See Picture Plane Environment
- Line of Sight ñ An imaginary straight line joining the observerís eye with the object viewed.
Mathematical Model ñ The set of x y z variable dimensions that define the length, width, height, size, shape and contours of an object, and from which a three-dimensional model or prototype can be built. -
- Monocular Vision ñ Literally, seeing with one eye. With monocular vision the perception of size or distance can only be inferred by comparison with other objects of known size or at known distances. Cameras and telescopes, for example, are monocular devices. (Photographs and "perspective" drawings are monocular perceptions. If viewed from other than the cameraís, or the artistís eye position, the pictures themselves are seen in perspective.)
 Offsets ñ Auxiliary x y z (length, width, height) dimensions that are added to (or subtracted from, as the case may be) the objectís entire set of primary x y z dimensions to make the object appear at a position on the picture plane different from dead center on CV.
-
One-point Perspective ñ A perspective projection in which one set of horizontal lines is parallel to the viewerís line of sight. The lines are foreshortened and they converge to a single vanishing point at the Center of Vision (CV) on the horizon. The other set of horizontals, and the verticals are parallel to the picture plane; they do not converge, and they can be measured. -
- Orthographicñ If an observerís eye position is at an infinite distance from an object, the rays from points on the object to the observerís eye will become parallel. The image projected onto the picture plane will be formed by perpendiculars from the object and will have its same dimensions. Thus, a three-view drawing is an orthographic projection. Also, see Perspective.
Parameter ñ A quantity whose value varies with the circumstances of its application. Also, see Attitude Parameters, Fixed Parameters, and Variable Parameters. -
- Perspective ñ If an observerís eye position is at a nearby distance from an object, the image projected on a picture plane where it is pierced by rays from the object will be practically the same as that formed in the observerís eye. Also, see Orthographic
- Perspective Projection ñ A three-dimensional object in pictorial form as it is seen on a two-dimensional picture plane where it is pierced by rays from points on the object to the observerís eye. The vehicle for the transformation is geometry, itself a branch of mathematics.
 Picture Plane (PP) ñ Technically, a transparent two-dimensional surface, perpendicular to the line of sight, on which an image is projected where it is pierced by rays from an object to the eye. In a more literal sense, it can be a sheet of paper, a canvas, a wall, a billboard or any flat surface suitable for the artist's purpose. The picture plane is ALWAYS perpendicular to the line of sight (the Central Visual Ray.)
 Roll ñAn angular measurement used to orient the object to the desired viewing aspect by rotating it about the line of sight (Z) axis of the picture plane. Also, see: Azimuth, Elevation and Rotation.
-
 Rotation ñ In mathematical perspective systems (Artistsí Perspective Modeler) the object is rotated about three mutually perpendicular axes on the picture plane to bring it to the desired viewing aspect. Azimuth (side to side) rotation is about the vertical (Y) axis. Elevation (up and down) rotation is about the horizontal (X) axis. Roll (circular) rotation is about the (Z) line of sight axis. Rotation can be about a single axis, or a composite of any two, or all three axes. Also, see Azimuth, Elevation and Roll.
Three-Dimensional Object ñ A material thing that occupies space. Trains, planes and automobiles, cereal boxes, cream pitchers, eagles, houses, horses and pyramids, to name a few, are three-dimensional objects; they have in common: width, length and height.  Three-Dimensional Projection ñ If the object is placed within a matrix of three mutually perpendicular transparent planes, Horizontal, Profile and Frontal, its image may be projected onto the planes to provide its three defining views: The Plan, Side and Front views. Conversely, when the planes of the three-view are arranged in the matrix form and projected inward, a three-dimensional image of the object may be formed. Also, see Auxiliary View, Three-View Drawing.
Three-Point Perspective ñ In three-point perspective, horizontal lines converge to points V1 and V2 on the Horizon line, above the eyelevel line (EL), and to the left and right of the CV. Vertical lines converge to V3 on a line perpendicular to the horizon line. The perpendicular line passes through the CV.
 Three-View Drawing ñ A basic three-view drawing describes the shape of an object and specifies its size in every detail. The views are usually: a plan (top) view, a side view and a front view placed adjacent to one another. Data provided by the views are: Length, Width and Height. Each adjacent view shares a dimension with its neighbor. Each view has a corresponding opposite view. Also, see Auxiliary View, Orthographic and Three-Dimensional Projection.
Trace ñ An imaginary line that remains on a surface where another surface or line has passed through it. The horizon line and the central vertical line on the picture plane are traces of the horizontal plane and the central vertical plane.
Two-point perspective ñ In two-point perspective, the sets of horizontal lines point in different directions and converge to vanishing points (V1 and V2) on the horizon to the left and right of the CV. If the projection is rotated 90† in either direction about the Line of Sight, the vanishing points will be above and below the CV, and the effect will be that of looking up, or down at the object. Also, see, One-Point Perspective, Three-Point Perspective.
Vanishing Line ñ A horizon line where parallel line sets converge in a point. Vanishing Point (VP) ñ A point on a horizon line to which any two or more lines that are in fact parallel, if extended indefinitely, will converge. Any system of parallel lines that is not parallel to the picture plane will appear to converge at a vanishing point. Also, see One-Point Perspective, Two-Point Perspective, and Three-Point Perspective.  Variable Parameters ñ The triad of x y z (length, width, height) dimensions that specify the location of a point in space relative to the o point of a three-dimensional object. (The table below shows the x y z values for the eight corners of a 3 x 3 x 3 cube.) Also, see Zero Point. Vertical Plane ñ See Picture Plane Environment illustration.
 Viewing Distance (D) ñ The true-length distance along the central visual ray from the eye position to the center of vision on the picture plane.
Zero Point ñ The intermediate point (o) between positive (+) and negative (ñ) values from which mutually perpendicular length, width, and height dimensions (x y z) of a three-dimensional object originate. Itís also the point of origin of the offsets, which are added to (or subtracted from, as the case may be) the entire set of variables to displace, or relocate, the object from CV on the picture plane. Also, see Offsets, Three-View drawing and Variable parameters.
-
|
