Those crossblended tiles look surprisingly nice. Also, I just realised that I wanted just such a tileset of white-to-black gradients to use for transparent shadow layers (to use as a demo or wiki article, once it's possible to modify map layer blending in the map editor). I wasn't sure which function to use, so thanks for this. Althoguh... those diagonal pieces are maybe not smooth enough to use for shadows, they draw too much attention. I suppose it can be fixed by adjusting the radius.
Placing such shadow tiles by hand is tedious so actually that's specifically something I wanted autotiling for.
It doesn't look great the because there is no art involved. I just wanted to explore the possibility. To make shadows, I think the function should be rotated 45 degrees on the Z axis. Also I suspect the derivative can be used as a bump map to make hills. I haven't tried that yet properly.
Same pattern but with no rotation on the left and with 45 degrees rotation on the right:
I just realized that there are 2 possible ways to generate the full size corner pieces, so I've updated the pattern.