@pimms.param<EOL><INDENT>def pre_affine(pa):<DEDENT>
return pa if pa is None else pimms.imm_array(to_affine(pa, <NUM_LIT:3>))<EOL>
proj.pre_affine is a 4x4 matrix of the affine transformation that should be applied to the
coordinates of the spherical mesh prior to projection via the rest of the standard map
projection methods. This may be None to indicate no initial transformation.