Foreshortening is the apparent contraction of a spatial dimension when an object, line, surface or scene extends partly or substantially in the depth direction relative to the observer and projection system. An object viewed increasingly along its length can appear shorter than the same object viewed more nearly across its length.
Foreshortening is one of the fundamental phenomena of perspective, but the term is frequently oversimplified. The Perspective Research Centre distinguishes two basic types of foreshortening which have different causes and can operate either separately or together:
- Aspect Foreshortening — Type 1: contraction caused by the orientation of the object, viewing angle or projection angle.
- Perspectival or Optical Foreshortening — Type 2: distance-dependent contraction or deformation arising from diminution of apparent size with increasing distance.
This distinction is essential. Aspect foreshortening can exist without distance-related diminution, as in parallel projection. In ordinary central, linear, visual and optical perspective, however, aspect and perspectival foreshortening normally operate together.
The Basic Principle of Foreshortening
Consider a long object viewed broadside. Most of its length extends across the observer’s field of view and therefore remains visually evident.
If the same object is progressively turned so that its principal axis points towards or away from the observer, less of its physical length is expressed across the resulting image. Its projected length becomes increasingly compressed.
At an extreme orientation, a long object can be viewed almost end-on. Its physical length has not changed, but very little of that length remains visible as projected image length.
This basic contraction with orientation is Aspect Foreshortening. When the object also extends through substantial depth from a finite viewpoint, different parts lie at different distances and consequently undergo different amounts of apparent size diminution. This introduces the additional component of Perspectival or Optical Foreshortening.
The Two Types of Foreshortening
The Dictionary divides the overall phenomenon into two basic contributing factors:
1. Aspect Foreshortening
Aspect Foreshortening is produced principally by orientation, viewing angle and projection angle. Dimensions extending towards or away from the observer project to a shorter image length than the same dimensions viewed more nearly perpendicular to the viewing direction.
It is notionally independent of distance. Equally oriented elements can undergo the same proportional contraction even when the projection system does not make distant objects progressively smaller.
2. Perspectival or Optical Foreshortening
Perspectival Foreshortening, also called Optical Foreshortening, is produced by the size–distance relationship of finite-viewpoint perspective. Different parts of an object extending through depth occupy different distances from the observer or projection centre and consequently possess different apparent or projected scales.
The nearer parts are represented at a larger scale than the farther parts. Intervals therefore become progressively smaller with increasing distance, producing a non-uniform transformation along the depth dimension.
Aspect Foreshortening — Type 1
Aspect Foreshortening is fundamentally an effect of how a spatial dimension is oriented relative to the viewing and projection arrangement.
A dimension seen approximately across the viewing direction displays much of its extent. As that dimension rotates towards the viewing direction, its projected length becomes shorter. The contraction is therefore related to the object’s aspect.
This process also changes apparent shape. A planar form viewed frontally may reveal its proportions relatively directly, while the same form viewed obliquely can appear compressed in one direction. The object itself has not changed; its projected form has changed because its orientation relative to the observer has changed.
Aspect Foreshortening can occur in natural vision, optical images, graphical constructions, mathematical perspective and technical projection. It also occurs in both converging and parallel projection systems.
Aspect Perspective and Foreshortening
Aspect Foreshortening belongs to the broader phenomenon of Aspect Perspective: changes in projected length, shape, angle or position caused by the orientation from which an object or scene is viewed or projected.
Aspect is therefore not simply another word for distance. An object can remain at essentially the same distance while being rotated. Its apparent shape can change dramatically even though the object has moved little or not at all towards or away from the observer.
A circle illustrates the general principle. Viewed square-on, it presents a circular aspect. Viewed at an increasing oblique angle, its projected form becomes progressively compressed in one dimension. The changing form results principally from aspect rather than from the circle becoming more distant.
Geometrical Projection Foreshortening
The Dictionary also associates Aspect Foreshortening with geometrical projection foreshortening.
This emphasises that the phenomenon can be understood geometrically. A spatial length projected onto another plane generally does not retain its full apparent extent unless its orientation has the appropriate relationship to the projection surface.
As the dimension becomes more strongly oriented into depth, its projected extent is reduced. This geometrical component can exist independently of optical diminution with distance.
Perspectival or Optical Foreshortening — Type 2
Perspectival Foreshortening is the distance-dependent component of foreshortening and is synonymous in the Dictionary with Optical Foreshortening.
It arises from the principle that apparent or projected size diminishes with increasing distance from a finite viewpoint. If an object extends substantially towards or away from the observer, its different parts therefore cannot possess one uniform image scale.
The nearer parts appear or are projected larger; the farther parts appear or are projected smaller. Consequently, equal physical intervals along the receding dimension occupy progressively different image lengths.
This produces the familiar non-uniform compression of objects, lines, grids and repeated structures extending into depth.
Why It Is Called Optical Foreshortening
The term Optical Foreshortening reflects its connection with the finite-viewpoint size–distance relationship found in visual and instrument perspective.
Natural vision, photography and other finite-centre optical systems exhibit diminution with distance. A receding spatial dimension is therefore represented at a continuously changing scale.
This contrasts with parallel projection, in which the projectors remain parallel and distance-related diminution does not operate. Parallel projection can therefore exhibit Aspect Foreshortening without exhibiting this second optical or perspectival component.
Foreshortening and Diminution of Size
Diminution of size and foreshortening are closely related but should not simply be treated as interchangeable terms.
Diminution of size describes the reduction in apparent or projected scale that occurs as distance increases. Perspectival or Optical Foreshortening describes how this size–distance effect contributes to the transformed appearance of a dimension or form that extends through depth.
An entire distant object can appear smaller because of diminution of size. A long object extending from a near position into a far position experiences different diminution along its own depth and therefore becomes non-uniformly transformed. This latter relationship contributes directly to perspectival foreshortening.
Uniform and Non-Uniform Foreshortening
The two types can also be distinguished by the character of their contraction.
Aspect Foreshortening is notionally proportional or uniform for features sharing the same orientation under a parallel or equivalent projection relationship.
Perspectival or Optical Foreshortening is distance-dependent and therefore generally non-uniform along the depth direction. A unit of physical length nearer the observer does not occupy the same projected size as an equivalent unit farther away.
Most ordinary real-space perspective views combine these two forms of transformation.
How the Two Types Combine
The central difficulty in understanding foreshortening is that Aspect Foreshortening and Optical Foreshortening frequently occur simultaneously.
Consider an object extending away from an observer. Its depth dimension is first contracted because the dimension is viewed obliquely or lengthwise. This is Aspect Foreshortening.
At the same time, successive parts of the object are farther from the finite viewpoint and therefore project progressively smaller. This is Perspectival or Optical Foreshortening.
The final visible or represented shape is produced by the interaction of both components. Treating the result as one undifferentiated phenomenon conceals the two different causes involved.
Can Optical Foreshortening Occur Without Aspect Foreshortening?
The Dictionary addresses this question directly for ordinary linear or focal perspective.
For a spatial plane or object extending through depth within a normal finite-viewpoint linear-perspective relationship, the answer is generally no. The depth-oriented structure is seen or projected at an angle, producing Aspect Foreshortening, while the size–distance relationship simultaneously introduces Optical Foreshortening.
The optical component may sometimes be very small — for example, where the object extends only a short distance in depth — but the size–distance relationship remains part of the finite-viewpoint system.
Can Aspect Foreshortening Occur Without Optical Foreshortening?
Yes. This is one of the clearest ways of distinguishing the two phenomena.
In parallel perspective, an object dimension can be projected at an oblique angle and therefore appear shortened. Aspect Foreshortening is operating.
However, the projectors remain parallel and there is no finite viewpoint producing progressive diminution of size with distance. Optical or Perspectival Foreshortening is therefore absent.
Parallel projection demonstrates that orientation-based foreshortening is a distinct phenomenon rather than merely another name for diminution with depth.
Foreshortening in Parallel Perspective
Parallel Perspective provides an important demonstration of pure Aspect Foreshortening.
The viewpoint is geometrically treated as lying at infinity and the projection lines remain parallel. Equal object dimensions therefore do not progressively diminish merely because they lie farther away.
Nevertheless, an axis or plane inclined relative to the projection surface can appear shorter than its actual length. The resulting contraction is caused by the projection angle and orientation, not by a change in distance-related scale.
This is why parallel and axonometric drawings can exhibit clear foreshortening even though their parallel edges do not converge towards ordinary finite vanishing points.
Axonometric Foreshortening
Axonometric Foreshortening is principally a form of Aspect Foreshortening.
The principal axes of an object are inclined relative to the projection plane. Their projected lengths therefore differ from their corresponding spatial lengths according to the selected axonometric arrangement.
In isometric, dimetric and trimetric projection, the different principal axes possess particular foreshortening relationships. These are geometrical projection effects rather than consequences of increasing distance from a finite viewpoint.
Axonometric foreshortening therefore provides one of the clearest technical examples of Type 1 foreshortening operating without Type 2.
Foreshortening in Orthographic Projection
Orthographic projection uses parallel projectors perpendicular to the projection plane.
A line or plane parallel to the projection surface can be shown without aspect contraction in the corresponding direction. A dimension inclined relative to the surface, however, projects to a shorter length and therefore exhibits Aspect Foreshortening.
No ordinary finite-viewpoint diminution is involved. Consequently, the foreshortening produced by an oblique orientation in orthographic projection belongs to Type 1 rather than Type 2.
Foreshortening in Oblique Projection
Oblique projection also separates projection-angle effects from ordinary optical recession.
The projection lines remain parallel but meet the projection plane obliquely. The scale assigned to the receding dimension can consequently differ from that used for the frontal dimensions.
Cabinet, Cavalier and other oblique systems employ particular depth relationships, but they do not reproduce the progressive distance-dependent diminution characteristic of central optical perspective.
Foreshortening in Linear Perspective
Linear Perspective normally combines both basic types of foreshortening.
A spatial dimension extending in depth is oriented away from the picture surface and viewing relationship and therefore undergoes Aspect Foreshortening. Because linear perspective also uses a finite station point, successive portions of that same dimension occupy different distances and undergo progressive diminution of apparent size.
The resulting perspective image therefore combines projection-angle contraction with distance-dependent scale change.
This combined operation is a defining feature of the characteristic appearance of receding surfaces, grids, roads, rooms, architectural structures and objects represented by central or linear perspective.
The Foreshortened Square
The foreshortened square provides a particularly clear example.
A square viewed directly face-on can retain a square appearance. If the plane containing the square tilts away from the observer, its depth-oriented dimension becomes compressed because of Aspect Foreshortening.
Under parallel projection, this aspect contraction can occur without progressive distance diminution.
Under central or linear perspective, however, the farther edge is also more distant from the station point and consequently projects smaller than the nearer edge. The final projected square therefore combines Aspect Foreshortening with Perspectival or Optical Foreshortening.
Foreshortening of a Ground-Plane Grid
The Dictionary uses the familiar perspective image of a square ground-plane grid to separate the two components analytically.
The transverse widths of successive grid divisions decrease with increasing distance. This is the direct effect of diminution of size.
At the same time, the dimensions extending away from the observer are seen at an inclined projection angle and appear contracted. This is Aspect Foreshortening.
The depth dimension also extends through increasing distance and is therefore additionally affected by optical diminution. Its overall appearance consequently combines the two mechanisms.
The familiar compressed grid of linear perspective should therefore not be explained as though one single phenomenon were responsible for every apparent shortening within it.
Foreshortening Is Not Confined to One-Point Perspective
The simple orthogonal ground grid is useful for explanation, but foreshortening is not confined to that special arrangement.
Objects, planes and line systems can occupy almost any direction relative to the observer, station point and picture plane. Their apparent lengths and forms change according to those relationships.
Foreshortening therefore occurs in one-, two-, three- and multi-point linear perspective, as well as in curvilinear, cylindrical, spherical, visual, optical, instrument, parallel and many other perspective systems.
The relative contribution of Aspect and Optical Foreshortening varies according to the particular geometry of each case.
Foreshortening in Two-Point Perspective
In two-point perspective, principal horizontal object dimensions can extend obliquely into depth in two different directions.
Each direction therefore has its own aspect relative to the observer and projection surface. The projected dimensions can be foreshortened by orientation while also changing in apparent scale as they extend towards their corresponding vanishing points.
Rotating the object changes these aspect relationships and therefore changes the apparent proportions of its visible faces, even where the object’s actual dimensions remain unchanged.
Foreshortening in Three-Point Perspective
Three-point perspective extends the same principles to a third principal spatial direction.
Vertical dimensions can now also extend significantly into depth relative to the projection arrangement. Consequently, they may undergo both orientation-based contraction and progressive distance-dependent scale change.
The resulting form can exhibit strong foreshortening along several principal axes simultaneously.
Foreshortening and Vanishing Points
Foreshortening and vanishing points frequently occur together in central or linear perspective, but they are not the same phenomenon.
A vanishing point identifies the projected limit of a spatial direction. Foreshortening describes the apparent contraction and transformation of dimensions associated with orientation and, in finite-viewpoint systems, changing distance.
A set of parallel receding lines may converge towards a vanishing point while the intervals and objects carried along those lines become progressively foreshortened.
Parallel projection demonstrates the distinction especially clearly: Aspect Foreshortening can occur even though parallel directions remain parallel and do not converge towards ordinary finite vanishing points.
Foreshortening and the Picture Plane
The apparent amount of Aspect Foreshortening depends upon the geometrical relationship between an object dimension and the relevant projection or picture surface.
Dimensions lying favourably relative to the picture plane can retain a greater projected extent. Dimensions turning increasingly into the depth direction occupy progressively less extent on the image surface.
This does not mean that picture-plane orientation alone explains foreshortening. The result belongs to the complete relationship between object orientation, viewing direction, station point, projection mode and picture or image surface.
Foreshortening and the Line of Sight
Foreshortening becomes especially pronounced when an object’s principal dimension approaches the observer’s viewing direction.
If a long object is viewed nearly end-on, its depth dimension can project into a comparatively short image dimension. If the same object is rotated towards a broadside orientation, much more of its physical length appears across the image.
The line of sight is therefore an important reference when describing a particular viewing relationship, but foreshortening should be understood through the complete projection geometry rather than by treating the sight line as the sole directional element of every perspective system.
Foreshortening of Lines
A straight spatial line can appear shorter than its physical length when its direction contains a significant depth component relative to the observer.
Under parallel projection, the shortening can be a uniform projection-angle effect. Under central perspective, different portions of a sufficiently long depth-directed line are also situated at different distances from the station point and therefore participate in a changing perspective scale.
The image length of a line must consequently not be assumed to reveal its true physical length unless the projection relationship permits such measurement.
Foreshortening of Planes
A plane likewise changes its projected shape as its orientation changes.
A rectangular plane viewed frontally may display much of its height and width. As it rotates away, one dimension becomes increasingly compressed. At an extreme edge-on condition, the visible projected area can approach a line.
This progression illustrates Aspect Foreshortening particularly clearly. If the plane simultaneously extends substantially through depth in a finite-viewpoint system, Optical Foreshortening also contributes to its final projected form.
Foreshortening of Solids
Three-dimensional solids can undergo simultaneous foreshortening of several dimensions.
Changing the viewpoint or rotating the object changes the relative aspects of its faces, edges and principal axes. Dimensions aligned more strongly into depth become compressed, while other dimensions may become more fully visible.
In a finite-viewpoint projection, nearer portions may additionally enlarge relative to farther portions. The resulting transformation affects the apparent proportions and outline of the whole solid.
Foreshortening of the Human Figure
The human figure provides a familiar and visually dramatic example of foreshortening.
An arm extended sideways is seen largely across the visual field. If the same arm points directly towards the observer, its length becomes strongly compressed by aspect.
At close viewing distances, the hand may also lie substantially nearer the observer than the shoulder. The hand therefore possesses a larger projected scale while the farther portions of the arm become progressively smaller.
The resulting image combines strong Aspect Foreshortening with strong Perspectival or Optical Foreshortening and can produce the exaggerated near-hand, compressed-arm appearance frequently exploited in drawing and illustration.
Close-View Foreshortening
Perspectival Foreshortening becomes particularly conspicuous when an object extends through a large depth range relative to its distance from the observer.
At close range, the difference between the distances of the nearest and farthest parts can be proportionally large. This creates substantial differences in projected scale along the object.
The resulting apparent proportions may therefore be dramatically different from those obtained from a more distant viewpoint, even though the physical object itself has not changed.
Distant-View Foreshortening
From a much greater viewing distance, the difference between the distances of the nearer and farther parts of a modestly sized object becomes relatively small.
The distance-dependent component of foreshortening can therefore become much less conspicuous, although orientation-based Aspect Foreshortening can remain substantial.
This demonstrates again that the two components need not contribute equally. Their relative strength depends upon the particular object, depth extent, orientation and viewpoint.
Foreshortening in Natural and Visual Perspective
Foreshortening is not merely a convention invented for perspective drawing. It is rooted in the changing appearance of spatial forms under natural viewing conditions.
In Visual Perspective Type 2, the apparent form of an object changes with viewpoint, orientation and distance. A dimension directed substantially towards the observer occupies less angular or retinal extent along its physical length than when viewed broadside.
If the object also extends significantly in depth, the changing distance of its parts contributes the size–distance component identified as Optical or Perspectival Foreshortening.
Foreshortening in Photography and Instrument Perspective
Camera and instrument images also exhibit foreshortening because they record spatial forms from particular viewpoints through defined projection systems.
A surface or body angled away from the camera undergoes Aspect Foreshortening. Where its parts lie at significantly different distances from the camera, finite-viewpoint diminution creates an additional non-uniform transformation.
Changing the camera position therefore changes foreshortening. Moving closer can greatly increase differences of projected scale between near and far parts, while moving farther away can reduce those differences.
Foreshortening in Graphical Perspective
Graphical perspective provides methods for constructing or representing the foreshortening that would occur under a selected geometrical system.
A graphical image can reproduce orientation-based contraction, distance-based diminution or both, depending upon the projection method employed.
Parallel graphical systems primarily employ Aspect Foreshortening. Central and linear graphical systems reproduce the combined relationships of aspect and finite-viewpoint diminution.
The drawing method does not itself make foreshortening an arbitrary artistic convention; it provides a means of constructing the corresponding geometrical transformation.
Foreshortening in Curvilinear and Spherical Perspective
The Dictionary also recognises foreshortening within curvilinear, circular and spherical perspective.
Changing object orientation continues to change projected aspect, while finite viewpoint and distance continue to affect apparent scale. What changes is the projection mapping through which those spatial relationships are represented.
Foreshortening is therefore not peculiar to a flat rectilinear picture plane. It belongs to the more general transformation of spatial dimensions into perspective appearance.
Foreshortening and Perspective of Form
Foreshortening belongs to the broader Perspective of Form: the transformation of the apparent geometry, shape, dimensions and proportions of objects and scenes under perspective.
Perspective of Form also encompasses phenomena including diminution of size, diminution or degradation of form, aspect changes and the geometrical organisation associated with vanishing structures.
Foreshortening is therefore one particular aspect of the much wider problem of how spatial Form is transformed into visible or represented Form.
Foreshortening and Apparent Shape
A physical object may retain a constant shape while presenting many different apparent shapes.
Foreshortening is one of the principal reasons for these changes. Dimensions oriented towards the viewing direction become compressed relative to dimensions more nearly across it.
Consequently, a known rectangular, circular, cylindrical or other regular form may project to an image whose proportions differ greatly from those of its familiar frontal or plan view.
The changed image does not mean that the physical form has been altered. It represents the appearance of that form from a particular spatial relationship.
Foreshortening and Depth
Foreshortening provides an important indication that a dimension extends through depth rather than merely across the picture surface.
A compressed apparent length can indicate that a longer physical dimension is directed towards or away from the observer. In a finite-viewpoint image, progressive changes of scale along that dimension provide further evidence of recession.
Foreshortening consequently contributes strongly to the visual interpretation and graphical representation of three-dimensional form.
Foreshortening as a Depth Cue
Because familiar forms change predictably with orientation and distance, foreshortening can function as a powerful depth cue.
An observer familiar with the likely physical dimensions of an object can interpret a strongly contracted image as evidence that the object extends significantly in depth.
The effect becomes particularly strong when combined with other perspective phenomena such as diminution of size, convergence, overlap, changes of apparent form and gradients of spatial recession.
Artistic Use of Foreshortening
Artists can reproduce foreshortening accurately, simplify it or deliberately exaggerate it.
A hand, foot, weapon, vehicle or other form projecting strongly towards the viewer can be enlarged relative to farther parts in order to emphasise depth, action or spatial immediacy.
The Dictionary specifically notes the familiar example of an outstretched arm in which the near hand or fingers are shown at a substantially different scale from the farther portions of the limb.
Such an image may amplify the perspectival or optical component while retaining the underlying aspect relationship of the figure.
Foreshortening and Measurement
A foreshortened image dimension cannot normally be read directly as the corresponding physical length without knowledge of the projection geometry.
Aspect Foreshortening has changed the projected extent according to orientation, while finite-viewpoint perspective may additionally have changed the scale according to distance.
This helps distinguish central perspective from technical parallel projections designed specifically to preserve selected measurements or consistent axis scales.
Foreshortening Is Relational
Foreshortening is not an intrinsic property permanently attached to an object.
The same object can appear almost unforeshortened from one direction and extremely foreshortened from another. Moving the observer, rotating the object, changing the projection arrangement or altering the relative orientation of the image surface can all change the resulting apparent form.
Foreshortening therefore describes a relationship between spatial Form and a particular viewing or projection condition.
Foreshortening Perspective
The Dictionary also uses the expression Foreshortening Perspective for a perspective image or view in which dimensions extending substantially into depth appear contracted relative to dimensions extending more nearly across the image.
This is a descriptive form rather than a third fundamental mechanism. The apparent contraction remains explicable through the two basic components: Aspect Foreshortening and Perspectival or Optical Foreshortening.
Foreshortening and the History of Linear Perspective
The history of perspective also reveals the importance of separating different kinds of foreshortening.
Various early systems of representation could employ changes of aspect or isolated diminution without possessing a fully unified finite-viewpoint linear-perspective construction.
Volume 1 emphasises that fully developed linear perspective systematically integrates several phenomena, including diminution with distance, Aspect Foreshortening, Perspectival Foreshortening and unified vanishing-point relationships.
The achievement of linear perspective therefore cannot be reduced simply to the discovery that an obliquely viewed object looks shorter.
Common Misconceptions about Foreshortening
Several common assumptions obscure the underlying geometry:
- There is not just one type of foreshortening. The PRC distinguishes Aspect Foreshortening and Perspectival or Optical Foreshortening.
- Foreshortening is not simply diminution with distance. Orientation alone can produce Aspect Foreshortening.
- Foreshortening is not simply a change of orientation. Finite-viewpoint size diminution can additionally produce non-uniform Perspectival Foreshortening.
- Parallel perspective can exhibit foreshortening. It exhibits Aspect Foreshortening even though ordinary distance-dependent Optical Foreshortening is absent.
- Vanishing-point convergence and foreshortening are not identical. They are related perspective phenomena with different definitions.
- An object does not physically become shorter when it is foreshortened. Its projected or apparent dimension is contracted.
- Foreshortening is not confined to the human figure. It applies to lines, planes, grids, architecture, objects, scenes and other spatial Forms.
- Foreshortening is not confined to one-point perspective. It can occur across many central, parallel, optical, graphical, curvilinear and spherical systems.
- Close viewpoints and wide depth ranges can greatly increase the optical component.
- The picture plane alone does not cause foreshortening. The effect depends upon the complete relationship of object orientation, viewpoint, projection direction, distance and projection surface.
Why Foreshortening Matters
Foreshortening is fundamental to perspective because it explains how spatial dimensions are transformed when they extend through depth rather than simply across the image.
Its two components expose two different geometrical causes that are easily confused: Aspect Foreshortening changes apparent form according to orientation and projection angle; Perspectival or Optical Foreshortening changes scale along depth according to distance from a finite viewpoint.
The distinction also connects several otherwise separate areas of perspective theory. It explains why parallel projection can show contracted dimensions without ordinary diminution, why central perspective combines orientation and size–distance effects, why close objects can exhibit dramatic scale differences between near and far parts, and why the apparent proportions of a spatial form change as the observer or object moves.
Understanding foreshortening therefore provides a foundation for understanding Aspect Perspective, Perspective of Form, diminution of size, station point, line of sight, picture plane, projection angle, vanishing points, linear perspective, parallel perspective, orthographic projection, axonometric perspective, oblique projection, Visual Perspective Type 2, Optical Perspective, Instrument Perspective, curvilinear perspective and spherical perspective.