@pimms.param<EOL><INDENT>def post_affine(pa):<DEDENT>
return pa if pa is None else pimms.imm_array(to_affine(pa, <NUM_LIT:2>))<EOL>
proj.post_affine is a 3x3 matrix of the affine transformation that should be applied to the
coordinates of the flat map after projection via the rest of the standard map projection
methods. This may be None to indicate no final transformation.