Hi all,
I’m trying to create clean cutouts (like donut shapes) from overlapping polygons in FME.
For example, lets say I have four geometries A, B, C, and D, with each progressively larger and fully containing/overlapping the smaller ones. I want to subtract the inner shapes from the outer ones (e.g. D minus C, B, A; C minus B, A; etc.) so that only the ring-like areas remain.
I’ve previously used the AreaOnAreaOverlayer with overlap counts to determine hierarchy (e.g. a shape with 1 overlap is the largest, and one with 3 overlaps is the smallest, so I can then figure out what is what).
However, this approach breaks when some of the smaller shapes are missing. I still need the output features to retain their original attributes (e.g. A, B, C, etc.), regardless of which shapes are present. For example, shape A might be missing, or both A and B but you’d never have A and C without B. So I need a method that can still produce correct results even when some of the smaller shapes aren’t there.
I’m exploring the Clipper transformer to do the subtraction. I suspect grouping might help (e.g. by ID or level), but I’m unsure how best to structure it so each larger shape clips against all smaller ones within the same group.
Any tips or examples would be much appreciated!
