category_id=-1

[xuyongzhi]

What does it mean when face category_id = -1? For example, 17DRP5sb8fy region0 face[78], category_id=-1, segment_id=-1, material_id=3659. There are totally 837 faces with category_id=-1. -1 category_id seems doesn't exist previously.

[DBobkov]

I think faces with category_id=-1 simply don't have a label.