with centre $S$
A mapping of a plane $\pi$ into a plane $\pi_1$ under which each point $M$ in $\pi$ is put into correspondence with the point $M_1$ of intersection of the straight line $SM$ with $\pi_1$ (if $SM$ is not parallel to $\pi_1$, see Fig.).
More generally, let $V$ and $V_1$ be proper subspaces of identical dimension in a projective space $\Omega$ and let $T$ be a subspace of maximal dimension not having points in common with $V$ or $V_1$. Let $U$ be a subspace contained in $V$, let $W$ be the subspace of minimal dimension containing $U$ and $T$ and let $U_1$ be the intersection of $W$ and $V_1$.
The correspondence by which each subspace $U$ contained in $V$ is put into correspondence with the subspace $U_1$ contained in $V_1$ is called a perspective mapping from $V$ into $V_1$ with perspective centre $T$.
A perspective is a collineation. If the subspaces $V$ and $V_1$ intersect, then each point in the subspace $V\cap V_1$ corresponds to itself.
If projective coordinates are introduced into the spaces $V$ and $V_1$, then a perspective correspondence can be specified by a linear mapping.
|||E. Artin, "Geometric algebra" , Interscience (1957)|
|||N.A. Glagolev, "Projective geometry" , Moscow (1963) (In Russian)|
Perspective mappings are also called central projections or perspectivities.
|[a1]||M. Berger, "Geometry" , I , Springer (1987)|
|[a2]||H. Busemann, P.J. Kelly, "Projective geometry and projective metrics" , Acad. Press (1953)|
|[a3]||H.S.M. Coxeter, "Introduction to geometry" , Wiley (1963)|
|[a4]||H.S.M. Coxeter, "Projective geometry" , Blaisdell (1964)|
|[a5]||H.S.M. Coxeter, "The real projective plane" , McGraw-Hill (1949)|
Perspective. Encyclopedia of Mathematics. URL: http://encyclopediaofmath.org/index.php?title=Perspective&oldid=31589