spacing.y and spacing.x in function core.utils.ijk2LPS should be swapped in Nifti scenario

[ppageon]

The function core.utils.ijk2LPS seems wrong in Nifti scenario, the original code as follow:

when I test a case with Nifti image with spacing like [0.5, 1.0, 0.75], the rendered images are distortion.

It looked fine when I swap the spacing.y with spacing.x, like:

So I think it should be wrong to multiply x component of Cos with y component of spacing, at least it doesn't work for Nifti scenario.