  We use the technique developed by Becchi and Imbimbo to construct a
well-defined BRST-invariant path integral formulation of pure spinor
amplitudes. The space of pure spinors can be viewed from the algebraic geometry
point of view as a collection of open sets where the constraints can be solved
and a free independent set of variables can be defined. On the intersections of
those open sets, the functional measure jumps and one has to add boundary terms
to construct a well-defined path integral. The result is the definition of the
pure spinor integration measure constructed in term of differential forms on
each single patch.
