The polygon may or may not be convex and cannot be rotated. The label is a rectangle that also cannot be rotated. I need the center of the biggest zone for placing the center of the label.
(Ideally would be to get a polygon of possible placements for the center of the label. That would allow disjointedly placing labels on overlapping polygons, but it would be too much...)
I'm using a Geometry Service (ESRI) which can test if a geometry (rectangle, polygon, etc) is inside another polygon (The irregular polygon.)