CSG

Constructive solid geometry (CSG) is a modeling technique used in computer graphics, computer-aided design (CAD), and 3D printing to create complex shapes by applying boolean operations to simple primitive solids such as cubes, spheres, cylinders, and prisms.

In CSG, models are represented as a tree where leaves are primitives and internal nodes are operations like union, intersection, and difference. Evaluating the tree combines solids to form the final shape. Parameters of the primitives and operands can be varied, making CSG a form of parametric modeling.

Typically, CSG models are converted to a polygonal mesh or boundary representation for rendering, simulation, or fabrication. The CSG approach maintains exact, boolean geometry for the primitives and precise editing, but some meshes require tessellation for display.

The idea emerged with the development of solid modeling in the 1960s–1980s; it became a standard approach in CAD tools and computer graphics. The term "constructive solid geometry" was widely used to describe this approach.

Applications: Used in CAD systems, solid modeling kernels (though many kernels rely on boundary representations), and 3D printing pipelines. OpenSCAD is a notable example that uses CSG to model objects.

Limitations and considerations: Best suited for models built from simple primitives and well-defined boolean operations. Less convenient for organic, freeform shapes. Numerical precision, degenerate intersections, and performance can be concerns for large trees.