If the region attribute in the first line is '1', each tetrahedra has an additional region attribute (an integer) in the last column. Region attributes of tetrahedra are tags used mainly to identify which tetrahedra of the tetrahedralization are associated with which facet-bounded region of the PLC, set in the part 4 of a .poly or a .smesh file. Region attributes do not diffuse across facets, all tetrahedra in the same region have exactly the same region attribute. A common use of the region attribute is to determine which material a tetrahedron has.
The .ele file is the default output file of TetGen if it generated a mesh or tetrahedralization. However, it can be omitted by -E switch. If -r switch is used, TetGen reads a .ele file and reconstructs a tetrahedral mesh from it.
The following example illustrates the layout of the .ele file.
154 4 0 1 4 107 3 50 2 4 108 3 107 3 9 97 95 94 4 4 107 50 93 5 56 1 50 47 6 94 98 97 95 7 97 9 95 55 8 52 55 5 51 ...