On output transformations for state linearization up to output injection

Steering a nonlinear system into a so-called state-affine one up to output injection, by change of coordinates, is of much interest for observer design. This interest is preserved by also considering changes of output. The purpose of the paper is then to provide computable conditions for existence of output transformations making a system which is not transformable into a state affine one up to output injection by only a change of coordinates to become so after a change of output. Such a characterization enlarges the class of systems for which an observer is available.