I have a patch that corrects this, but it caused other problems. The origin, centre and the corner points of the renderers matched, but the crosshair was not exactly in the middle of the voxels.

I found a simple workaround for the issue in our app that does not need modifications in MITK.

I leave this ticket open because I would be curious if you consider this as a bug, or the half voxel shift is intended. If the latter, it might be worth mentioning it in the Geometry Introduction page. Now it says that for non-image geometries the origin is the bottom-left-back corner of the bottom-left-back voxel, but for renderers it seems that it is point at the middle of the bottom-left edge of the bottom-left-back voxel, instead.

The patch is here, by the way:

https://github.com/NifTK/MITK/tree/bug-17618-trac-3285-crosshair-not-at-voxel-centre

Any thoughts on this?

Do I think correctly that the centre point and the the eight corner points (not considering the order) should match in each render window and the image geometry that was used to initialise the renderers?

Pull request sent:

https://github.com/MITK/MITK/pull/61

The commit:

https://github.com/NifTK/MITK/commit/0237348a55155bd6aedf1d2bcbe1159ac897b93d

The change compared to the previous patch is that the correct spacing is set for the transformation matrix before the offset is corrected.

The scaling was hard coded to 1, 1, -1 for flipped geometries, what probably did not cause any problem for image geometries, since there the origin of the first slice is the same as the origin of the 3D volume. This is not true for non-image geometries, though.

Please let me know if you can merge it, because we are in the process of an MITK upgrade, and if it gets merged quickly, I do not put it on the top of our fork.

Esther and Michel, could you please have a look at this bug and the related pull request?