[Insight-users] How to get the 3d coordinates ?

Rupert Brooks rupe.brooks at gmail.com
Fri Aug 29 10:16:12 EDT 2008


Hi Yuting,

In this and your other email, im thinking that i dont fully understand
your question.  I'll make an attempt to answer anyway.  The ITK
registration framework defines the transform such that it maps points
from the coordinate system of the fixed image into that of the moving
image.   So after registration, for any particular point in the fixed
image, you can get the corresponding point in the moving image
using (roughly):

TransformType::Pointer mytransform=TransformType::New();

...
// registration happens
...

itk::Point<double,IMAGE_DIMENSION>
movingPoint=myTransform->TransformPoint(fixedPoint);
.... do something with the transformed point
// here fixed point is the point in the fixed image, and moving point
is the point in the moving image.

If you have many points, you have to loop over all the points.

When resampling an image - this approach resamples the moving image
into the space of the fixed.  This is because images are warped in
reverse to guarantee coverage of the entire lattice.  Im going to
guess - because this always gives people headaches - that you probably
want to go from a moving image point to the fixed image point.   Maybe
you want to warp a mesh the same way as an image?  This is not always
easy - you have to invert the transform.  Matrix based transforms
(rigid, affine, etc) - if thats what you have - are invertible, (using
the GetInverse() method)  but deformable transforms are not closed
form invertible.

Please let me know if this is helping with your question at all.

Cheers
Rupert B.

2008/8/28 王宇亭 <wytwyt218 at hotmail.com>:
> Hi all.
>     In image registration, if fixed image is corresponded to a 3d surface
> mesh, then after the moving image is mapped to the fixed image, I can get
> the 3d coordinates of the moving image by interpolating based on the 3d
> coordinates of the fixed image.
>     How can I implement this using the ITK codes?
>     Thanks a lot!
>
>     Yuting
>
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Rupert Brooks


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