bool_combine
Combine, merge 2 polygons (must have common part). The order of fg/bg is irrelevant.
Category: boolean
bool_intersect
Get intersection of 2 polygons (must have common part). The order of fg/bg is irrelevant.
bool_substract
Substract bg to fg polygons (must have common part). The fg/bg order is crucial.
bool_xor
Substract bg to fg polygons (must have common part). The order of fg/bg is irrelevant.