  The level-set method is a popular method for interface capturing. One of the
advantages of the level-set method is that the curvature and the normal vector
of the interface can be readily calculated from the level-set function.
However, in cases where the level-set method is used to capture topological
changes, the standard discretization techniques for the curvature and the
normal vector do not work properly. This is because they are affected by the
discontinuities of the signed-distance function half-way between two
interfaces. This article addresses the calculation of normal vectors and
curvatures with the level-set method for such cases. It presents a
discretization scheme that is relatively easy to implement in to an existing
code. The improved discretization scheme is compared with a standard
discretization scheme, first for a case with no flow, then for a case where two
drops collide in a shear flow. The results show that the improved
discretization yields more robust calculations in areas where topological
changes are imminent.
