Hi @zilvinas_fme​ , you can use Orientor to reverse the orientation of surface. Isn't it your desired function?

Hi Takashi,

I started with Triangulator and received triangles used with GeometryCorcer to convert to fme_polygon.

But GeometryCorcer all results was "untouched".

The feature output from the Triangles port of Triangulater has a MultiArea geometry which consists of multiple polygons, and GeometryCoercer considers it as a kind of polygon geometry, so outputs it from the Untouched port.