vtkImageInterpolator when original image direction was -1 for an axis

Hello,
I have an application that successfully uses vtkImageInterpolator that ultimately use DICOM data read in by ITK. These data sets display correctly even when the z direction is -1, but the interpolator does not work when the data coordinate is less than the origin.

It is possible that the problem originates in my use of vtkVolumePicker to pick the point, but this appears well behaved, in returning a coordinate smaller than the value of the origin, as makes sense for the direction being negative, and the point it returns is correct in the volume.

Resetting the origin doesn't help, as the picker still returns a coordinate smaller than the (new) origin - it seems to just slide all numbers down.

Rotating the image so as to make the direction of the z axis positive does make it work - but then the display causes an unintended mirror image problem (e.g., the aorta comes in front of the heart rather than staying behind the heart in a chest image).

I am sure it must be obvious but I have not yet seen what to do.

Thank you,
Andy

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