[Insight-developers] Image as an OrientedImage Progress

[Rupert Brooks]

Steve, Luis, Kent,

One reason this suggestion stirred me out of my usual inertness is
that i could see it breaking a heck of a lot of code of mine.  In
short, it scared me :-)

As Luis pointed out, theres an issue of backwards compatibility, and
thats what my concern amounts to.

Sadly, i dont have a great solution to this issue.  If i have 2D
images that have three direction cosines, i treat them as a volume one
voxel thick.

I like Steves suggestion - the current status quo becomes the case
when spatial dimension==image dimension.  This addresses the issue of
backwards compatibility nicely, while allowing images embedded in a
higher dimension for those whose applications require it.

Rupert

On Mon, Sep 22, 2008 at 11:39 AM, Steve M. Robbins <steve at sumost.ca> wrote:
> 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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-- 
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Rupert Brooks