at the moment I work on implementing cascades for my Light Propagation Volumes implementation and I always have "problems" with the different cell sizes and the results produced by this.
First a picture of the Problem ( I only draw indirect light here, the bottom plane is white and the light Comes from straight above):
As you can see the 3 different cascades are clearly visible, and now a picture where I draw spheres for each cell shaded with the spherical harmonic of this cell (of the cascade with the smallest cells and the one with the biggest cells) :
Here you can see where the problem is, in both displayed cascades the light comes from straight above and therefore the cells near to the bottom are the brightest, thats fine. (The blue line is the bounding box of the cascade with the smallest cell size)
And in both cascades the first 1- 3 or 4 levels of cells (from bottom to top) are receiving a considerable amount of light. The problem is that the cell size is different and therefore in the end with greater cell size the light seems to travell much further than with small cells and this is the problem.
To me this problem is clear and I really have no idea how to really solve this. In the papers about cascaded light propgation volumes, they dont seem to have this problem or because of the fact that usually the center of all cascades is centered around the camera (with some offset sometimes) it might not as obvious but I dont really believe that, they must do something different.
Another way would be to use the cellsize in the propagation of light and try it with a quadratic or some kind of falloff, but even the you would see a difference just because of the different positions of the brightest cells.
My feeling is that there is no really solution, just some fixes which makes this a little bit smoother like Interpolation between cascade borders.
So far I tried to handle each cascade independently and in another approach I even propagate light between cascades which is a little bit better but the described problem is in both cases clearly visible.
If some one has any thoughts or ideas I would really appreciate it.