Different Geometry Types and Formats in CAD

Constructive solid geometry (CSG) is a modeling technique used in CAD systems to create a complex geometry by combining parametric features and Boolean operations. CSG presents a solid or surface that appears visually complex, but is actually little more than cleverly combined or uncombined objects (primitives, extrusion, revolution, sweep, filet, chamfer, shaft, ...). The CAD system usually translates a CSG modeling into a BREP geometrical representation during an update of the construction tree. Therefore, it is necessary to have performed an error-free update before exporting in a neutral format to ensure that the BREP representation conforms to the design intent.

Boundary Representation is a method for representing shapes using the limits. it is often abbreviated as B-Rep or BREP in CAD modeling. A solid is represented as a collection of connected surface elements, the boundary between solid and non-solid. Boundary representation models are composed of two parts: topology (faces, edges and vertices) and geometry (surfaces, curves and points). An edge is a bounded piece of a curve and a vertex lies at a point. A face is a bounded portion of a surface. These geometry is commonly called "precise geometry".
Manifold solids have the property that, at every point on the boundary, a small enough sphere around the point is divided into two pieces, one inside and one outside the object. Non-manifold models break this rule.

Tessellation is a triangular approximation to represent precise geometry in a light representation. SAG parameter is set to control the approximation by defining the maximum distance between the triangle and the surface.