  We show that a central linear mapping of a projectively embedded Euclidean
$n$-space onto a projectively embedded Euclidean $m$-space is decomposable into
a central projection followed by a similarity if, and only if, the least
singular value of a certain matrix has multiplicity $\ge 2m-n+1$. This matrix
is arising, by a simple manipulation, from a matrix describing the given
mapping in terms of homogeneous Cartesian coordinates.
