> You are right--changing the aspect ratio didn't fix the problem.. So is
> the rendering problem with non-cubic grids a VisAD bug or VisAD feature?
VisAD implements volume rendering as sets of planes perpendicular
to the X, Y and Z axes. The choice of axis changes as the box
rotates, to the axis closest to parallel with the view direction.
This techniques is widely used (and first described in my paper
to the 1989 volume visualization workshop), but does produce weird
images when volumes are very non-square like your 61 x 61 x 5. Try
Curtis's suggestion of resampling to 61 x 61 x 61.