A “drawing” is a visual technique that depicts forms, ideas, or objects on a two-dimensional surface by making lines, marks, or tonal areas. It can refer to the act of creating a piece of art or the final illustration itself.
Artistic Method
Let us consider how an artist produces a perspective drawing/painting of a three-dimensional scene. Patently, the artist must first select a subject to paint (an object/scene) to be viewed from a fixed location, the so-called station or viewpoint. One might assume that the artist can begin by simply sketching what he/she sees whilst looking at the scene in a somewhat ad hoc manner. But normally, it is necessary to fix the viewpoint, viewing angle, and field of view in some way, because there are a large number of possible viewing angles and contrasting scene aspects or points of view that can be observed, each from a slightly different viewpoint and/or viewing angle, etc.
The problem is that the artist’s viewing location, plus angle-of-view, can (possibly) change whilst the drawing is under construction. To solve this problem, a ‘transparent’ frame is overlaid on the spatial scene, called the perspective window or windowpane (which may be purely imaginary and can even be wholly or partially unconscious). This perspective window is normally rectangular, and planar (or flat) in form, and serves the purpose of fixing the artist’s head position (location), plus angle of vision and field of view (monocular eye position), relative to the spatial scene/object in question.
Ergo, the artist begins by looking at a scene through an imaginary perspective window (or even a real glass window or semi-transparent veil), and the drawing/painting is made as if coincident with this flat and translucent windowpane. Whereby, for a representation created in such a manner, each painted object in the scene is thus depicted as a flat, scaled-down image of the object on the other side of the window. Thus, the technique of graphical perspective works by representing the light that passes from a scene through an imaginary rectangle (represented as the plane of the drawing/painting), to the viewer’s eyes (ostensibly a single eye).
Viewing a Perspective Artwork
What happens when another person looks at a painting created in this way?
Well, it’s as if the viewer were (him or herself) looking through the same perspective window and hence viewing a representation identical to the original scene (at least in some senses, and not including binocular optical/perceptive effects). This happens because each portion of the painted object lies on the same straight line from the viewer’s eye to the equivalent portion of the real object it represents. Henceforth, the viewer ostensibly sees no difference between the painted scene on the perspective window and the real-world view of the spatial scene/object.
For a painting so constructed, the picture plane can be thought of as the glass of the notional windowpane through which the viewer looks into the representation of spatial reality that lies beyond. In practice, the picture plane is the same as the physical surface of the painting produced in this manner. When the resulting picture or representation is viewed from the same spot as the windowpane was created (or from an identical station point located the same distance in front of the picture), then the depicted image is geometrically identical to what was seen through the unpainted window (by the artist).