[Insight-users] inverting deformation fields

[Anja Ende]

Oh yes, of course! That is a subtle point.

May I ask a follow up question then? In inverting a deformation field then,
how do we decide the sampling of this grid of the inverse field?

Say our original deformation field has a displacement at every voxel and
these displacement vectors can point to any real location. So, is the
inverse deformation field going to be calculated at these real locations?
However, we need to have a uniform grid and this is not guaranteed by this
scheme now. Can someone explain this to me on how this is done?

Sorry for asking these naive questions. I could use the ITK filters out of
the box but I would like to know some of these basics.

Thanks,
Anja


On 10 April 2013 20:06, Matt McCormick <matt.mccormick at kitware.com> wrote:

> Hi Anja,
>
> If displacement vector field gives the displacement at location x, but
> the negative of the displacement at location x is not the inverse;
> what is required is negative of the displacement vector at x + \delta
> x.
>
> HTH,
> Matt
>
> On Wed, Apr 10, 2013 at 5:47 PM, Anja Ende <anja.ende at googlemail.com>
> wrote:
> > Hello all,
> >
> > This is a very naive question and I would be very grateful if someone can
> > clarify this doubt for me.
> >
> > I see that there are quite a few filters and some very sophisticated
> methods
> > for inverting deformation fields.
> >
> > If I have a dense deformation field, why is it not enough to simply
> negate
> > the displacement vector to compute the inverse? I am sure there is a
> simple,
> > logical explanation for this but I am having trouble figuring it out.
> >
> > Thanks a lot for your help!
> >
> > Anja
> >
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