The db-class where the active samples will serve in defining their convex hull

The db-class where the selection derived from the convex hull will be applied

When a selection already exists, the 'combine' keyword indicates how the current selection must be combined with the previous one. For more information on the available keywords, check db.selcombine.

When a selection already exists and a new selection is created, the previously existing selection is deleted beforehand if this flag is TRUE. Otherwise a new variable is created.