Determines the type of the current group.
(tpm_cleangrouptype clean_id)
Returns a type code or nil.
| clean_id | Model ID returned by tpm_cleanalloc |
| 1 | Erase short objects |
| 2 | Break crossing objects |
| 4 | Extend undershoots |
| 8 | Delete duplicates |
| 16 | Snap clustered nodes |
| 32 | Dissolve pseudo nodes |
| 64 | Erase dangling objects |
| 128 | Simplify objects |
| 256 | Zero length objects |
| 512 | Apparent intersections |
| 1024 | Weed polylines |