Thanks Gerry - that is exactly correct.

Let me just add a few details. When you are working with a series of concatenated transformations, you must invert each of them, and you must also reverse their order. That's because the inverse of A*B*C is C^-1*B^-1*A^-1.

So if reformatx gets: "a.xform b.xform c.xform", then streamxform would need to get "--inverse c.xform --inverse b.xform --inverse a.xform".

And keep in mind that when your transformations are B-spline FFDs (i.e., what comes out of, say, warp and warpx), then the inverse is approximated numerically, and this approximation may sometimes fail when the transformation is highly nonrigid and perhaps even folded.

Hope this helps.

Torsten


Originally posted by Gerry Sun: