[Insight-users] Applying a transform to the orientation/origin of an image

[Johnson, Hans J]

We do this all the time in our BRAINSFit program
http://www.nitrc.org/projects/multimodereg.

We wrote an Insight-Journal article and an ITK filter for doing this.

http://www.insight-journal.org/browse/publication/770

Hans


On 2/7/11 8:56 AM, "max power" <zouookmoetenwerken at gmail.com> wrote:

>Hi all,
>
>I'm trying to transform an image based on a rigid euler 3d transform
>that is generated by our code by matching some landmarks.  Normally
>I'd resample, but in this case, I would like to just 'impose' this
>transform onto the orientation of the image, so that I can use it
>in-place.
>
>My guess is that ChangeInformationImageFilter is the key component
>here, but I'm not 100% sure that I understand all the intrinsics of
>applying a transform to both the origin/center as well as the
>directions of an image.
>
>Lets assume I've succesfully built a VersorRigid3DTransform transform,
>by feeding a number of landmark points in _physical space_ to a
>LandmarkBasedTransformInitializer.
>
>Would something along these lines make sense:
>
>    typedef itk::ChangeInformationImageFilter< ImageType > ChangerType;
>    ChangerType::Pointer ch = ChangerType::New();
>    ch->SetInput( image );
>
>    ch->SetOutputOrigin( transform->GetTransform()->TransformPoint(
>image->GetOrigin() ));
>
>    ImageType::DirectionType dir = image->GetDirection() *
>transform->GetMatrix();
>    ch->SetOutputDirection( dir );
>
>    ch->SetChangeDirection( true );
>    ch->SetChangeOrigin( true );
>    ch->Update();
>
>I guess I'm on the right path, but applying the transform like above
>does not work, even after fiddling extensively with the order of the
>operations (or even applying inverses).  The resulting images do not
>seem to match my generated transform at all.
>
>I hope to find a way so that the following holds, where old_image is
>the untransformed image, and new_image is the output of the
>changeinformation filter:
>
>   transform.transformpoint( old_image.indextophysical( p ) ) ~=
>new_image.indextophysical( p )
>
>Any tips on how to approach this would be most welcome!
>
>Regards,
>Jorik
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