Acces to polygons from navmesh

Hi. I need to read polygons whith python script from blender’s generated navmesh (to export whith my own format). I try D.objects[trimesh_name].data.polygons but it returns only triangles (Recast calculate polygons, but blender triangulate this polygons). I read at documentation “The index of the navigation polygon the face belongs to stored in the layer CD_RECAST of the face custom data”. I think this data is helful for me, but i don’t undestand how acces it. Anybody can help me?

Sorry if i explained badly, my english is not good :frowning:

Thanks a lot.