It has been known that the Wigner representation theory for positive energy
orbits permits a useful localization concept in terms of certain lattices of
real subspaces of the complex Hilbert -space. This ''modular localization'' is
not only useful in order to construct interaction-free nets of local algebras
without using non-unique ''free field coordinates'', but also permits the study
of properties of localization and braid-group statistics in low-dimensional
QFT. It also sheds some light on the string-like localization properties of the
1939 Wigner's ''continuous spin'' representations.We formulate a constructive
nonperturbative program to introduce interactions into such an approach based
on the Tomita-Takesaki modular theory. The new aspect is the deep relation of
the latter with the scattering operator.Comment: 28 pages of LateX, removal of misprints and extension of the last
section. more misprints correcte