[Insight-users] still struggling with TransformPhysicalPointToIndex

[Bill Lorensen]

David,

I haven't had a chance to look at the data you gave. It's still on my todo list.

This is independent of the corner/center issue.

Bill

On Fri, Mar 13, 2009 at 4:21 AM, David Pastor <david.pastor at die.upm.es> wrote:
>  Hi!
>
>  I commented days ago some possible problems with this method. I've received
> some feedback about it, but not sorted out yet!
>
> There is a whole review on this about a bug or bad implementation as it was
> using truncation instead of rounding or flooring. Also there was some
> discussion about making the transformation corned-based or centre-based. I
> don't know which is the status of this in the current version.
> My problem is that the same PointType element is transformed to different
> IndexType elements in images that only differ on the dimension (same
> SizeType and same SpacingType). I double-checked the header files and
> everything is consistent.
>
> Particularly, the size on the z axis is different (one pixel distance)
> between a 3D image and the same frame in a 4D image. I think the dimension
> should not affect in here.
>  It seems that the truncation could be an issue, but as u said it will
> affect the two images instead and not just one of them. Otherwise the
> center-based vs corner-based problem is not a big deal here.
>
>  What i don't really understand is what TransformPhysicalPointToIndex
> does... as far as i understand it only should divide each coordinate by the
> scaling,  round or floor the value and make the transformation from
> center-based
>  coordinates to a corner-based index count (which is mainly add the offset).
>
>  I'm just considering doing this process by myself and see what happens.
>
> Someone suggested something about the "loop unrolling in
> itk::ImageTransformHelper".
> Cheers
> David
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