The ROI selector can generate an area that is a combination of polygons; overlapping polygons create a hole in the area.

There are separate tabs to add a rectangle, a circle or a regular polygon with any number of vertices, and with separate size/position attributes. The "Add" button will add a new polygon to the area polygon list; the "Replace" button will erase all existing polygons prior to adding the new one.

The polygons are stored as text with a configurable number of significant digits. By selecting the "All polygons" tab, each polygon can be inspected or edited (as text), or deleted.