The goal of the CGAL Open Source Project is to provide easy access to
efficient and reliable geometric algorithms in the form of a C++ library. CGAL
is used in various areas needing geometric computation, such as: computer
graphics, scientific visualization, computer aided design and modeling,
geographic information systems, molecular biology, medical imaging, robotics
and motion planning, mesh generation, numerical methods... More on the
projects using CGAL web page.

The Computational Geometry Algorithms Library (CGAL), offers data structures
and algorithms like triangulations (2D constrained triangulations and Delaunay
triangulations in 2D and 3D, periodic triangulations in 3D), Voronoi diagrams
(for 2D and 3D points, 2D additively weighted Voronoi diagrams, and segment
Voronoi diagrams), polygons (Boolean operations, offsets, straight skeleton),
polyhedra (Boolean operations), arrangements of curves and their applications
(2D and 3D envelopes, Minkowski sums), mesh generation (2D Delaunay mesh
generation and 3D surface and volume mesh generation, skin surfaces), geometry
processing (surface mesh simplification, subdivision and parameterization, as
well as estimation of local differential properties, and approximation of
ridges and umbilics), alpha shapes, convex hull algorithms (in 2D, 3D and dD),
search structures (kd trees for nearest neighbor search, and range and segment
trees), interpolation (natural neighbor interpolation and placement of
streamlines), shape analysis, fitting, and distances (smallest enclosing
sphere of points or spheres, smallest enclosing ellipsoid of points, principal
component analysis), and kinetic data structures.