Polynomial relations are established between the invariants of certain
mixed sets of points and lines and the invariants of their projected
images. The relations are obtained using the properties of a rational
curve which is a covariant of the given set of points and lines. Numer
ical experiments indicate the level of performance which can be expect
ed from a recognition system based on one of the relations. (C) 1998 E
lsevier Science B.V.