[Insight-users] VectorImage Orientation from NRRD

[Daniel Betz]

Hello ITK developers,

An itk::Image that behaves the same like itk::OrientedImage will
facilitate a very clean and nice interface to NRRD files, I am very
glad about that.

One thing remains. I am afraid to peeve too much with that and
don't want to be misunderstood. I starred a long time on some
coordinates on my screen and nothing made sence. And there are
still questions.

itkNrrdImageIO.cxx. I am using at the moment revision 1.30. The
cvs commit entry for revision 1.31 was: "now handles LPS to/from
coversion for 3D images".

There is apparently no public information available about a
convention for ITK to load orientated images into an unorientated
image only in LPS space.

Somebody told me, that people are "freaking out" when they get
images with another orientation as DICOM. The sign flipping
methode in the file loaders is definitly the wrong way to adress
this issue. If the matter is, that people are not aware of the
different coordinates, the application could make a red border
around the window, tinker the coordinate letters or prevent
loading or something like that if the world space is not LPS.
Anyway, if conversion is "well defined" the application can do
that.

I remembered that Slicer3 was loading and showing my NRRD file
properly and took a look into the file Slicer3/Libs/vtkTeem/
vtkNRRDReader.cxx. I found a similar mechanism, probably from
the same author; this time LAS and LPS are flipped to RAS.
(by the way, the default branch of the switch statement is very
enlightening). I don't know enouth about VTK to say if such a
conversion makes sence here, but I am in doubt.

My impression is, that the transformations in the file readers
were a mistake, which nobody wants to correct in deference to the
author or something like that.

Finally, I only want some insight, and I want it stable, reliable
and especially predictable.

Regards
Daniel Betz
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