  The concept of creating digital twins, connected digital models of physical
systems, is gaining increasing attention for modeling and simulation of whole
cities. The basis for building a digital twin of a city is the generation of a
3D city model, often represented as a mesh. Creating and updating such models
is a tedious process that requires manual work and considerable effort,
especially in the modeling of building geometries. In the current paper, we
present a novel algorithm and implementation for automatic, efficient, and
robust mesh generation for large-scale city modeling and simulation. The
algorithm relies on standard, publicly available data, in particular 2D
cadastral maps (building footprints) and 3D point clouds obtained from aerial
scanning. The algorithm generates LoD1.2 city models in the form of both
triangular surface meshes, suitable for visualisation, and high-quality
tetrahedral volume meshes, suitable for simulation. Our tests demonstrate good
performance and scaling and indicate good avenues for further optimization
based on parallelisation. The long-term goal is a generic digital twin of
cities volume mesh generator that provides (nearly) real-time mesh manipulation
in LoD2.x.
