[ITK Community] [Insight-users] inverting a deformation field - problem

[Tim Bhatnagar]

I appreciate the response, Brad.

Can you tell me how the implementation of the 'WarpImageFilter' works, such
that when I input my Demons-generated displacement field, and my
'movingImage' (from Demons) as input, I get what looks like my 'fixedImage'
(from Demons) as output... making me think that the displacement field is
actually mapping my movingImage into my fixedImage?

Also, I use Paraview to visualize my field, and when visualized, it
illustrates what you are suggesting (the mapping that would take fixed ->
moving). But how then, does the WarpFilter use the SAME FIELD to warp my
movingImage into a very nice estimation of my fixedImage?

Sorry if any of that is convoluted..


On Mon, Dec 9, 2013 at 6:00 AM, Bradley Lowekamp <brad at lowekamp.net> wrote:

> Hello,
>
> It not uncommon for resampling-type algorithms to have some points be
> mapped out side the the domain. This is why a boundary condition and
> extrapolators are used. If there are just a limited number of pixel being
> mapped out side, then the simplest way be by to just check if the pixel is
> within the image's region.
>
> ITK's registration frameworks solve for a transform which maps from the
> "Fixed" image to the "Moving" image. This is well described int Chapter
> Eight of the old Software guide:
>
> http://www.itk.org/ItkSoftwareGuide.pdf
>
> Brad
>
> On Dec 8, 2013, at 6:38 PM, Tim Bhatnagar <tim.bhatnagar at gmail.com> wrote:
>
> Hello,
>
> I've created a displacement field via Demons non-rigid registration. I am
> now trying to create the inverse (using
> InverseDisplacementFieldImageFilter), but when I am using the indexes to
> ascribe the inverted field, my program crashes mid-way through, because it
> appears I am trying to call a *negative* index (specifically, the 3rd
> index parameter.. the 'z'-parameter).
>
> I don't do anything to the displacement field except write it to a vtk
> file before i invert it.. can anyone suggest a solution? I thought I could
> try and specify the 'direction' of the field, but I'm not sure where in my
> pipeline I can set the direction of the *inverted* displacement field...
>
> sorry if that's messy.. any thoughts would be appreciated!
>
> Thanks,
>
> Tim
>
> --
> Tim Bhatnagar
> PhD Candidate
> Orthopaedic Injury Biomechanics Group
> Department of Mechanical Engineering
> University of British Columbia
>
> Rm 5000 - 818 West 10th Ave.
> Vancouver, BC
> Canada
> V5Z 1M9
>
> Ph: (604) 675-8845
> Fax: (604) 675-8820
> Web: oibg.mech.ubc.ca
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>


-- 
Tim Bhatnagar
PhD Candidate
Orthopaedic Injury Biomechanics Group
Department of Mechanical Engineering
University of British Columbia

Rm 5000 - 818 West 10th Ave.
Vancouver, BC
Canada
V5Z 1M9

Ph: (604) 675-8845
Fax: (604) 675-8820
Web: oibg.mech.ubc.ca
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