[Insight-developers] Image as an OrientedImage Progress

[Steve M. Robbins]

On Mon, Sep 22, 2008 at 08:53:27AM -0400, Rupert Brooks wrote:
> I've used ITK for a lot of image registration tasks, including some
> not exclusively medical ones.  In computer vision and geomatics work,
> 2D images that are really 2D are pretty common.   Genuinely 2D in that
> there is not particularly an implied third dimension.  In this case,
> having a 2x2 set of direction cosines makes perfect sense.    For me,
> conceptually speaking, a 2D slice that is embedded in a 3D volume is
> actually a 3D volume, one voxel thick, and should be read as a 3D
> image.
> 
> I'm definitely not a fan of embedding all 2D images in 3D.

Neither am I.  Fortunately, I don't think that is being proposed.

The status quo, where all 2D images are embedded in a 2D space
regardless of what the image format says, is equally bad.

The crux of the matter is, as Bill said in the beginning, is there are
really two dimensions to an image.  

> > On 9/16/08 9:57 AM, "Bill Lorensen" <bill.lorensen at gmail.com> wrote:
> >
> >> This issue has been raised before.
> >> See http://public.kitware.com/Bug/view.php?id=5573
> >>
> >> There are really two "dimensions" of an image.
> >>
> >> 1) ImageDimension is the number of dimensions in the image container,
> >> 1, 2, 3, ...
> >> 2) I'll call it SpatialDimension, the number of dimensions in the
> >> coordinate system of the image. This dimension is the dimension used
> >> for origin, spacing and the direction.

Is it possible that the Image class could simply acquire a new
template parameter for SpatialDimension?  But then there are 4D
coordinate systems where one dimension is time; you might have a
2D or 3D slice out of a 4D space and desire the origin and direction
cosines to use the 3D spatial coordinates.

So maybe some kind of helper class for coordinates is the way to go,
akin to the image container class?  The helper class would know the
structure of the embedding space and be able to return sensible point
and vector classes suitable for, e.g., the origin and the direction
cosines.

-Steve

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