Semi-global invariants of piecewise smooth Lagrangian fibrations

We study certain types of piecewise smooth Lagrangian fibrations of smooth symplectic manifolds, which we call stitched Lagrangian fibrations. We extend the classical theory of action-angle co-ordinates to these fibrations by defining certain invariants which give a semi-global classification of germs of stitched fibrations. We then describe stitched fibrations with monodromy in terms of these invariants.