Different Geometry Types and Formats in CAD

CSG Model

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.



B-REP modelBoundary 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.


Faceted modelTessellation 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.



Neutral format Proponents File Extension Geometry Type
 3D PDF  Adobe  PDF  Either or Both
 JT  Siemens PLM - ISO  JT  Either or Both
 ACIS  Spatial - DS  SAT  Either or Both
 Parasolid  Siemens PLM  X_B, X_T, XMT, XMT_TXT  B-REP
 PRC  Tech Soft  PRC  Either or Both
 STEP  ISO  STP, STEP, STPZ  Either or Both
 Stereolithography  3D systems  STL  Tesselation
 Universal 3D  ECMA  U3D  Either or Both
 VRML  Web3D, VRML  WRL, VRML  Tesselation
Proprietary Formats Vendor File Extension Geometry Type
 Catia V4  Dassault Systèmes  MODEL, SESSION, DLV, EXP  Both
 Catia V5  Dassault Systèmes  CATPART, CATPRODUCT  B-REP
 Catia V5  Dassault Systèmes  CGR  Tesselation
 Catia V6  Dassault Systèmes  3DXML  Tesselation
 Pro/Engineer  PTC  ASM, NEU, PRT, G (granite)  Both
 Creo View  PTC  ED, EDZ, PVS, PVZ, OL  Both
 I-DEAS  Siemens PLM  MF1, ARC, UNV, PRT, ASM, PKG  Both
 NX  Siemens PLM  PRT  Both
 Inventor  Autodesk  IPT, IAM  Both
 Solid Edge  SIemens PLM  ASM, PAR, PWD, PSM  Both
 SolidWorks  Dassault Systèmes  SLDASM, SLDPRT  Both