[Insight-users] itk::Image vs. itk::OrientedImage

[Daniel Betz]

Hello,

I have an itk::Image with orientation like this:

origin:[-125, -124.1, 79.3]
spacing:[0.9375, 0.9375, 3]
direction:
1 0 0
0 1 0
0 0 -1

Now I take a valid pixel index:

Pixel Index: [134, 112, 11]

and ask with itk::Image::TransformIndexToPhysicalPoint() for the coordinates
in physical space and get:

Physical Point: [0.625, -19.1, 112.3]

This is not a physical point inside my image, because the direction of the
z-axis is negativ. So the z-component 112.3 is outside of my image, because
the image starts at origin 79.3 (z-axis).

Reading the source code I determined, that 
itk::Image::TransformIndexToPhysicalPoint()
does not take direction into account.

But there is the class itk::OrientedImage which handles the orientation
correctly.

My question is, why is SetDirection() in itk::Image available, since the
Transform Methods will not use it anyway. Why has itk::Image only a
"fake orientation" and why I need itk::OrientedImage for a
"real orientation" ?
The design decission to handle it that way is not visible for
me.

In the Doxygen documentation of itk::Image is written, that some functions are
implemented differently in itk::OrientedImage. I think that is not enough and
it should be documented more explicitly that I can set the direction in an 
itk::Image even though it will not taken into account by the transform 
methods.

Sincerly
Daniel Betz
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