Parallel perspective is an ambiguous term that has been used for two substantially different systems of spatial representation. In one meaning, it refers to a form of one-point linear perspective. In another, it refers to systems in which projecting lines remain parallel and do not converge.
Because these meanings describe different geometrical processes, the term should be used with care. Wherever possible, a more precise name—such as one-point perspective, parallel projection, orthographic projection, oblique projectionor axonometric projection—should be preferred.
What Is Parallel Perspective?
Parallel perspective may refer to:
- a linear-perspective arrangement in which a principal face of an object is parallel to the picture plane and perpendicular receding lines converge towards one vanishing point; or
- a non-converging system in which the projecting lines remain parallel as they pass from the object to the projection plane.
The Getty Art & Architecture Thesaurus recognises both meanings. It also recommends using terms such as parallel projection, axonometric drawing or a narrower technical term when describing architectural representations. (Getty)
These two meanings should not be treated as geometrically equivalent.
Parallel Perspective as One-Point Perspective
In the first meaning, parallel perspective is another name for one-point perspective.
The object is arranged so that one of its principal faces is parallel to the picture plane. The horizontal and vertical edges of that face remain horizontal and vertical in the image, while edges extending perpendicular to the picture plane recede towards a single vanishing point.
This arrangement is commonly used to represent:
- rooms and corridors;
- roads, railways and tunnels;
- frontal views of buildings;
- boxes and other geometrical forms;
- repeated objects extending directly into depth.
Merriam-Webster defines parallel perspective in this sense as linear perspective in which object lines perpendicular to the drawing surface are represented as meeting at a point on the horizon, and identifies it as one-point perspective. (Merriam-Webster)
The word parallel therefore refers primarily to the frontal face being parallel to the picture plane. It does not mean that the receding lines remain parallel in the finished image. Those lines converge towards the vanishing point.
Basic characteristics
In this form of parallel perspective:
- one principal face is parallel to the picture plane;
- one principal direction recedes perpendicular to the picture plane;
- receding parallel lines converge towards one vanishing point;
- the vanishing point normally lies on the eye-level line in a level view;
- frontal horizontal and vertical lines remain parallel to the corresponding edges of the image.
For clarity, the Perspective Research Centre recommends calling this system one-point perspective rather than parallel perspective.
Parallel Perspective as Parallel Projection
In its second meaning, parallel perspective refers to a system in which the projection lines remain parallel and do not converge towards a finite viewpoint.
This is more accurately called parallel projection.
Unlike ordinary linear perspective, parallel projection does not represent distant objects as progressively smaller merely because their distance from the projection plane increases. Equal parallel dimensions can therefore remain equal throughout the drawing.
Parallel projection is widely used where the clear communication of form, dimensions and spatial relationships is more important than reproducing ordinary optical appearance. It is especially important in engineering, architecture, technical illustration, design, mapping and computer graphics.
Principal types of parallel projection
Parallel projection includes two broad families:
Orthographic projection
The projecting lines are parallel to one another and perpendicular to the projection plane.
Orthographic projection includes:
- plan views;
- elevations;
- sections;
- multiview drawings;
- axonometric projections.
Oblique projection
The projecting lines remain parallel but meet the projection plane at an oblique angle rather than at right angles.
Oblique systems include forms such as:
- cavalier projection;
- cabinet projection;
- plan oblique projection.
Orthographic and oblique projection may both communicate three-dimensional form, but they use different relationships between the object, the projectors and the projection plane.
Axonometric Projection
Axonometric projection is a form of orthographic parallel projection in which the object is turned so that several of its principal faces or axes can be shown simultaneously.
Its principal forms are:
Isometric projection
The three principal axes are treated equally and undergo equal foreshortening.
Dimetric projection
Two principal axes share the same scale or foreshortening, while the third differs.
Trimetric projection
Each of the three principal axes has a different scale or degree of foreshortening.
Axonometric images can present several sides of an object at once while preserving measurable and systematic relationships. The projectors remain parallel rather than converging towards vanishing points. (Cambridge University Press)
Although axonometric drawings are sometimes described informally as forms of perspective, they differ fundamentally from central or linear perspective.
Parallel Perspective and Linear Perspective
The essential difference concerns the relationship between the projecting lines.
Linear or central perspective
- projection lines converge at a finite viewpoint;
- parallel spatial directions may converge towards vanishing points;
- apparent size changes with distance;
- the image approximates selected features of optical appearance.
Parallel projection
- projection lines remain parallel;
- no finite viewpoint is used;
- corresponding parallel edges need not converge;
- size does not diminish solely because of increasing depth;
- dimensions and geometrical relationships can be preserved more directly.
Parallel projection can therefore suggest depth without reproducing the same diminution and convergence found in central perspective.
Why the Term Is Confusing
The ambiguity arises because parallel perspective may describe either:
- an object face positioned parallel to the picture plane in a converging one-point construction; or
- parallel projection lines that do not converge at all.
In the first system, spatially parallel receding lines converge in the image.
In the second system, the projectors and many represented directions remain parallel.
The same expression therefore refers to both a converging and a non-converging form of representation. Without further explanation, a reader may not know which meaning is intended.
Parallel Systems in East Asian Art
Non-converging spatial arrangements occur in many East Asian paintings, prints, handscrolls and architectural representations. Parallel or approximately parallel edges may be maintained rather than directed towards a single fixed vanishing point.
Such images may also combine:
- elevated or shifting viewpoints;
- successive areas of space;
- overlapping forms;
- vertical displacement;
- changes in scale;
- oblique architectural axes;
- multiple moments or locations within one composition.
The Getty Art & Architecture Thesaurus associates one meaning of parallel perspective with systems in which parallel projecting lines do not converge and notes that this approach is common in East Asian painting. (Getty)
This does not mean that all East Asian art uses one uniform system. Chinese, Japanese and Korean traditions contain numerous methods of organising pictorial space, and individual works may combine several spatial principles.
Parallel perspective should therefore be treated as one descriptive category rather than as a complete explanation of East Asian pictorial space.
Parallel Perspective Is Not Reverse Perspective
Parallel perspective should also be distinguished from reverse perspective.
In parallel projection, corresponding receding lines remain parallel.
In ordinary linear perspective, they converge away from the observer.
In reverse perspective, they may diverge into depth and appear to converge towards a point situated in front of the image or towards the observer.
These are three different directional arrangements:
- linear perspective: convergence into pictorial depth;
- parallel projection: neither convergence nor divergence;
- reverse perspective: divergence into pictorial depth.
Recommended Terminology
To avoid ambiguity, the following terms are recommended:
Use one-point perspective when a frontal face is parallel to the picture plane and receding perpendicular lines converge towards one vanishing point.
Use parallel projection when the projectors remain parallel and do not converge.
Use orthographic projection when the projectors are perpendicular to the projection plane.
Use oblique projection when parallel projectors meet the projection plane obliquely.
Use axonometric projection for an orthographic parallel projection showing several principal sides or axes of an object.
Use isometric, dimetric or trimetric projection when the particular axonometric relationship is known.
The expression parallel perspective may still be used when discussing historical terminology, particular artistic traditions or an established source, but its intended meaning should always be explained.
Is Parallel Projection Really Perspective?
Whether parallel projection should be classified as perspective depends partly upon how broadly the word perspective is defined.
Under a narrow definition, perspective is restricted to central projection from a finite viewpoint. Parallel projection would then be treated as a separate system.
Under a broader definition, perspective includes systematic methods of projecting, organising and representing spatial relationships on a surface. Parallel projection may then be included as one family within the wider field.
The Perspective Research Centre adopts the broader interdisciplinary approach while continuing to distinguish clearly between:
- central projection;
- parallel projection;
- optical appearance;
- visual perception;
- graphical construction.
This allows the different systems to be compared without suggesting that they operate identically.
Key Points
Parallel perspective has two principal meanings.
It may refer to one-point perspective, in which a frontal face is parallel to the picture plane and receding lines converge towards one vanishing point.
It may also refer to parallel projection, in which the projectors remain parallel and do not converge.
Because these processes are fundamentally different, more precise terminology should be used wherever possible.
Continue Exploring
- Basic Perspective Drawing
- Linear Perspective
- Graphical Perspective
- Mathematical Perspective
- Axonometric Perspective
- Reverse Perspective
- Dictionary of Perspective