  This paper introduces a watertight technique to deal with the boundary
representation of surface-surface intersection in CAD.
  Surfaces play an important role in today's geometric design. The mathematical
model of non-uniform rational B-spline surfaces (NURBS) is the mainstream and
ISO standard. In the situation of surface-surface intersection, things are a
little complicated, for some parts of surfaces may be cut-off, so called
trimmed surfaces occur, which is the central topic in the past decades in CAD
community of both academia and industry. The main problem is that the
parametric domain of the trimmed surface generally is not the standard square
or rectangle, and rather, typically, bounded by curves, based on point inverse
of the intersection points and interpolated. The existence of gaps or overlaps
at the intersection boundary makes hard the preprocessing of CAE and other
downstream applications. The NURBS are in this case hard to keep a closed form.
In common, a special data structure of intersection curves must be affiliated
to support downstream applications, while the data structure of the whole CAD
system is not unified, and the calculation is not efficient.
  In terms of Bezier surface, a special case of NURBS, this paper designs a
reparameterization or normalization to transform the trimmed surface into a
group of Bezier surface patches in standard parametric domain [0,1]X[0,1]. And
then the boundary curve of normalized Bezier surface patch can be replaced by
the intersection curve to realize watertight along the boundary. In this way,
the trimmed surface is wiped out, the "gap" between CAD and CAE is closed.
