It’s a bit of a special case related to reservoir simulations. I try to calculate the liquid level in each cell for a given saturation. For this I need to clip each cell (which can be any shape, including a polyhedron) through multiple points (each of its vertex elevations, plus more auxiliary levels), and calculate the volume of the clipped part. Using vtkTableBasedClipDataSet would be inefficient since it would clip the whole dataset for each required elevation.