u32 tri_group_index This data is ignored since NIFF 2.0 uses the geometry data specified by the shape_tri_link that is specified in Shape. u32 tri_index As of NIFF 2.0, the index number specified by this data is the index number of Tri in TriGroup, EnvelopeTri in Envelope or ClusterTri in ClusterShape. The type of node and the index number of TriGroup, Envelope and ClusterShape are distinguished by shape_tri_link and kind_of_node_for_geometry of the Shape node that is linked by this Part.