Basic Concepts and Terminology
In considering linear perspective it is necessary to return to the concept of the picture plane. As defined previously, the picture plane is the actual two dimensional surface of your paper or canvas. The image you create on that surface is drawn as if you were seeing your subject through the picture plane.
The other key concept to understand is the horizon line, which is, of course, the horizon; it is also your eye level. When you sit looking out a window at an ocean view, the horizon appears near the bottom of the window. When you stand, the horizon appears higher in the window. If you are tall enough or the window is low enough, the horizon will be above the top of the window.
Imagine a plant in a flowerpot hanging outside the window. If you can see inside the top of the flowerpot, the horizon line will be high in the window, because you are looking down. If you see the bottom of the pot, the horizon line will be low in the window, because you are now looking up. So, when you draw, if you want to give your viewer the impression of looking up, put the horizon line low on the page. To give the impression of looking down, put the horizon line high on the page.
Study the list of terms below so that you can more easily grasp the text and illustrations that follow.
The picture plane is the actual surface of your drawing or painting. The image is what you imagine you see behind the picture plane.
Ground line: A line drawn to establish the surface on which an object rests; it is used to determine accurate vertical measurements in perspective drawings. The ground line is always parallel to the horizon line. When making a perspective drawing that shows top and side views, you place the side view of an object on the ground line.
Horizon line: The actual horizon, where earth and sky appear to meet, excluding obstructions like hills or mountains. Also called eye level.
Parallel: Said of any two lines or surfaces that are always the same distance from each other.
Perpendicular: At a right, or 90 degree angle to a given line or plane. An absolutely vertical line and an absolutely horizontal line are perpendicular to each other.
Picture plane: The surface of your paper or canvas. The image you create on the picture plane gives the impression that your subject is behind this surface.
Plane: Any flat surface, such as a wall, floor, ceiling, or level field.
Station point: The artist's position relative to the object he or she is drawing.
Vanishing point: A point at which parallel lines receding into space appear to converge. If the lines are parallel to the earth they will meet. on the horizon line.