torus_type	Description
UF_MODL_DOUGHNUT_TORUS	The torus us not self-intersecting (a>b)
UF_MODL_APPLE_TORUS	The outer part of a self-intersecting torus (a<=b, a>0)
UF_MODL_LEMON_TORUS	The inner part of a self-intersecting torus (a<0, |a|<b)
UF_MODL_OSCULATING_APPLE_TORUS	The limiting case a=b is allowed. It is referred to as an osculating apple, but there is no lemon surface corresponding to this case.
UF_MODL_NOT_A_TORUS	The limiting case a = 0 cannot be represented as a torus. It is a sphere.