[Insight-users] ITK Image Coordinates / Problem with Physical Point to Index Conversion

[Andreas Keil]

Hi,

I think I have discovered an inconsistency between the ITK Software Guide
(p.40) and the implementation of itk::Image (all the methods taking
physical points / continuous indices as arguments):

The trunctation of continuous index coordinates to integers does not yield
the correct pixel coordinates as expected by looking at the definition in
the software guide.

A simple example is:
Image spacing: 1mm
Image origin: 0mm/0mm

The pixel with index (1/1) would (according to the software guide) have
the following extents:
0.5mm/0.5mm to 1.5mm/1.5mm

However, the physical point 0.6mm/0.6mm gets mapped to the index 0/0 by
the method TransformPhysicalPointToIndex.

The solution would be to check those conversion methods as well as others
(like IsInside) and replace integer truncations with rounding.

If my reasoning is correct, I'll file a bug report. However, I'd like to
have some confirmation first.

Thanks,
Andreas.