World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0023912960
Reproduction Date:

Title: Perspectivity  
Author: World Heritage Encyclopedia
Language: English
Subject: Czech Technical University in Prague, Projective geometry, Ellipse
Collection: Composition in Visual Art, Functions and Mappings, Perspective Projection, Projective Geometry, Technical Drawing
Publisher: World Heritage Encyclopedia


In geometry and in its applications to drawing, a perspectivity is the formation of an image in a picture plane of a scene viewed from a fixed point.


  • Graphics 1
  • Projective Geometry 2
    • Projectivity 2.1
    • Higher-dimensional perspectivities 2.2
    • Perspective collineations 2.3
  • Notes 3
  • References 4
  • External links 5


The science of graphical perspective uses perspectivities to make realistic images in proper proportion. According to Kirsti Andersen, the first author to describe perspectivity was Leon Alberti in his De Pictura (1435).[1] In English, Brook Taylor presented his Linear Perspective in 1715, where he explained "Perspective is the Art of drawing on a Plane the Appearances of any Figures, by the Rules of Geometry".[2] In a second book, New Principles of Linear Perspective (1719), Taylor wrote

When Lines drawn according to a certain Law from the several Parts of any Figure, cut a Plane, and by that Cutting or Intersection describe a figure on that Plane, that Figure so described is called the Projection of the other Figure. The Lines producing that Projection, taken all together, are called the System of Rays. And when those Rays all pass thro’ one and same Point, they are called the Cone of Rays. And when that Point is consider’d as the Eye of a Spectator, that System of Rays is called the Optic Cone[3]

Projective Geometry

A perspectivity:
ABCD \doublebarwedge A'B'C'D',

In projective geometry the points of a line are called a projective range, and the set of lines in a plane on a point is called a pencil.

Given two lines \ell and m in a plane and a point P of that plane on neither line, the bijective mapping between the points of the range of \ell and the range of m determined by the lines of the pencil on P is called a perspectivity (or more precisely, a central perspectivity with center P).[4] A special symbol has been used to show that points X and Y are related by a perspectivity; X \doublebarwedge Y . In this notation, to show that the center of perspectivity is P, write X \ \overset {P}{\doublebarwedge} \ Y. Using the language of functions, a central perspectivity with center P is a function f_P \colon [\ell] \mapsto [m] (where the square brackets indicate the projective range of the line) defined by f_P (X) = Y \text{ whenever } P \in XY.[5] This map is a projection since it is an involution, that is, f_P (f_P (X)) = X \text{ for all }X \in [\ell].

The existence of a perspectivity means that corresponding points are in perspective. The dual concept, axial perspectivity, is the correspondence between the lines of two pencils determined by a projective range.


The composition of two perspectivities is, in general, not a perspectivity. A perspectivity or a composition of two or more perspectivities is called a projectivity (projective transformation, projective collineation and homography are synonyms).

There are several results concerning projectivities and perspectivities which hold in any pappian projective plane:[6]

Theorem: Any projectivity between two distinct projective ranges can be written as the composition of no more than two perspectivities.

Theorem: Any projectivity from a projective range to itself can be written as the composition of three perspectivities.

Theorem: A projectivity between two distinct projective ranges which fixes a point is a perspectivity.

Higher-dimensional perspectivities

The bijective correspondence between points on two lines in a plane determined by a point of that plane not on either line has higher-dimensional analogues which will also be called perspectivities.

Let Sm and Tm be two distinct m-dimensional projective spaces contained in an n-dimensional projective space Rn. Let Pn-m-1 be an (n-m-1) - dimensional subspace of Rn with no points in common with either Sm or Tm. For each point X of Sm, the space L spanned by X and Pn-m-1 meets Tm in a point Y = fP(X). This correspondence fP is also called a perspectivity.[7] The central perspectivity described above is the case with n = 2 and m = 1.

Perspective collineations

Let S2 and T2 be two distinct projective planes in a projective 3-space R3. With O and O* being points of R3 in neither plane, use the construction of the last section to project S2 onto T2 by the perspectivity with center O followed by the projection of T2 back onto S2 with the perspectivity with center O*. This composition is a bijective map of the points of S2 onto itself which preserves collinear points and is called a perspective collineation (central collineation in more modern terminology).[8] Let φ be a perspective collineation of S2. Each point of the line of intersection of S2 and T2 will be fixed by φ and this line is called the axis of φ. Let point P be the intersection of line OO* with the plane S2. P is also fixed by φ and every line of S2 that passes through P is stabilized by φ (fixed, but not necessarily pointwise fixed). P is called the center of φ. The restriction of φ to any line of S2 not passing through P is the central perspectivity in S2 with center P between that line and the line which is its image under φ.


  1. ^ Kirsti Andersen (2007) The Geometry of an Art, page 1,Springer ISBN 0-387-25967-9
  2. ^ Andersen 1992, p. 75
  3. ^ Andersen 1992, p. 163
  4. ^ Coxeter 1969, p. 242
  5. ^ Pedoe 1988, p. 281
  6. ^ Fishback 1969, pp. 65-66
  7. ^ Pedoe 1988, pp. 282-3
  8. ^ Young 1930, p. 116


  • Andersen, Kirsti (1992), Brook Taylor's Work on Linear Perspective, Springer,  
  • Fishback, W.T. (1969), Projective and Euclidean Geometry, John Wiley & Sons 
  • Pedoe, Dan (1988), Geometry/A Comprehensive Course, Dover,  
  • Young, John Wesley (1930), Projective Geometry, The Carus Mathematical Monographs (#4), Mathematical Association of America 

External links

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.