These constants define any additional data assigned to the vertex.

Values:

IG_VECT_VERTDATA_NONE	The vertex does not have any additional data.
IG_VECT_VERTDATA_BULGE	The outgoing line is bulged.
IG_VECT_VERTDATA_THICKNESS	The outgoing line has a local thickness.
IG_VECT_VERTDATA_WEIGHT	The vertex has weight. Used with rational Bi splines.