ÃÛÌÒTV

The Bondi-Sachs formulation of general relativity led to the nonlinear understanding of the gravitational radiation of an isolated object. This formulation is used to rigorously calculate gravitational waves at null infinity using Cauchy-Characteristic-Extraction methods. In this talk I present novel initial models using this formulation for vacuum spacetimes and for spacetimes of relativistic stars with rotation. I discuss the necessary regularity conditions at the vertex of the null cones and how the initial models are derived from a quasi-spherical approximation of the Bondi-Sachs metric.