[Insight-users] Final transformation question

[Anja Ende]

Hello,

Last question about adding displacement fields, I promise!

So, I have a displacement/position field that takes me from image C to
image B (so in the space of image C).

Then, I have another displacement field that takes me from image B to
image A (so in space of image B).

Now, what I want to do is combine them to go from image C to image A.

So, can I do the following:

- Generate a displacement grid in the space of image C.
- For every physical point in the grid, transform it to corresponding
points in space of image B.
- (This part has me a bit confused). If the point lies outside the
image, mark that particular voxel with some value like nan.
- For the voxels that are in image B, add the displacement fields (by
calculating the nearest voxel index through nearest neighborhood
interpolation). Can I do something better here?

The resultant displacement field with take me from C to A and I can
then resample image A in the space of C.

Does this seem sound reasoning or can I do something better?

I would really appreciate any input you can give me on this.

Many thanks,

Anja