Hi @JoeJ,

I finally managed to get sometime to do some testing. While thinking about some of the points you raised, I decided to double check on how I was first generating the depth cubemap. When I first wrote the code, I had saved every image of the cubemap just to check that these were indeed being created correctly. Yes, these created correctly BUT not in the right order. I was confused with the labeling of the cubemap orientations. After fixing this, it all looks good. Here is an example,

Here is the first derivative in the vertical direction,

So many thanks for your suggestions which made me recheck this!