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The geometric modeling kernel is a software component used to provide 3D modeling capabilities in computer-aided design (CAD) software. It is used to design virtual models to support the simulation and manufacturing of real objects. The geometric modeling kernel uses various geometric representations to represent real objects. These models include small planar models that roughly estimate objects using triangular surface meshes, as well as B-rep models that precisely define solid models using mathematically defined surfaces. Many kernels provide a wide range of modeling tools. For example, 2D sketches can be swept or rotated into 3D solids, or Boolean operations can be used to add, subtract, or combine 3D solids. Advanced kernels provide direct model editing tools such as draft, shelling, and offset, and also support the creation of very large models and complex freeform surfaces. The geometric modeling kernel supports interoperability between software based on the same kernel without conversion. This can improve model stability and performance when conveying 3D design intent between CAD software and computer-aided manufacturing (CAM) and computer-aided engineering (CAE) software.
1. Basic Functions of Geometric Kernels
The geometric kernel mainly includes data structures and corresponding algorithms for mathematical, geometric, and topological objects; as well as file import/export functions that enable the import of IGES models, STEP models, and other standard file formats, and can be uniformly converted to proprietary file formats. Non-core requirements can also be referred to as extensibility requirements, mainly including general or specific functions aimed at simplifying user operations.
1) Basic Mathematical Objects: Data structures and related operations for points, vectors, lines, planes, coordinate systems, matrices, coordinate transformations, etc.;
2) Geometric Objects: Data structures for points, lines, and surfaces, supporting 7 types of curves and 9 types of surfaces;
3) Geometric Operations: Also known as geometric calculations, mainly including intersection, projection, reflection, coordinate transformation, etc.;
4) Topological Elements: Using B-Rep to describe the topological structure, the main hierarchical topological structures include: Vertex, Edge, Loop, Face, Shell, Lump, Body;
5) Topological Relationships: Include topological dependencies and the associations between topological elements and geometric elements, the former refers to the search for adjacency and dependency relationships between points, edges, and faces, while the latter refers to the mapping relationship from topological elements to geometric elements;
6) Topological Operations: Also known as topological calculations, mainly including stretching, rotation, array, Boolean operations, sweeping, lofting, filleting, drafting, thickening, etc.;
7) General Mechanisms for Object Management: Creating and deleting object collections, object creation and deletion, object checking, stream and unstream, disk read and write, persistent references;
8) Discretization: The operation of discretizing parameter curves, surfaces, and solids into several triangles and points, providing data sources for display engines, etc.;
9) Implementing Proprietary File Formats, Implementing import/export functions for data expression of single entities;
10) The national standard number for IGES (The Initial Graphics Exchange Specification) is GB/T 14213, corresponding to the US national standard US PRO/IPO-100; the current IGES national standard number is GB/T 14213-2008, corresponding to IGES 5.3;
11) The latest standard support for STEP AP242, as well as compatibility with AP203 and AP214 standards.
2. Mainstream Geometric Kernels
Currently, the mainstream commercial 3D geometric kernels are ACIS and Parasolid. These two 3D kernels share a common origin, just two branches of development. ACIS’s Spatial company was acquired by Dassault, while Parasolid has undergone multiple acquisitions and is now owned by Siemens. The current two commercial kernels, in addition to strengthening the underlying kernel functions, ACIS is more inclined towards applications in CAD/CAE/EDA/CAM and other customer application fields, while Parasolid is more inclined to strengthen Siemens’ own business support, with Parasolid being superior to ACIS in CAD functionality.
Most of the 3D CAD software on the market, as well as the geometric kernels of 3D geometric modeling simulation software, use ACIS or Parasolid.
Currently, the open-source geometric kernel is Opencascade, launched by a French company, which is a good choice for small project development.
2.1 ACIS
ACIS is a product of American Spatial Technology Company, a geometric platform used for CAD system development. It provides modeling functions from simple solids to complex solids, as well as various editing functions such as Boolean operations, surface trimming, and surface transitions, and also provides data storage functions for solids and SAT file input/output functions.
The characteristics of ACIS are that it uses an object-oriented data structure, programmed in C++, allowing for arbitrary flexible combinations of wireframe modeling, surface modeling, and solid modeling. Wireframe modeling defines objects using only edges and vertices; Surface modeling is similar to wireframe modeling, but it defines the visible faces of the object; Solid modeling represents the size, shape, density, and properties (weight, volume, centroid) of the object.
ACIS products use software component technology, allowing users to use the required components or replace ACIS components with their own developed components. ACIS products include a series of ACIS 3D Toolkit geometric modeling and various optional software packages, with a package being similar to one or more components, providing some advanced professional functions that can be sold separately to users needing specific functions. ACIS products can sell interface source code externally and encourage various software companies to develop integrated manufacturing systems compatible with the STEP standard based on the ACIS core development system. The underlying products using the ACIS engine mainly include AutoCAD, Inventor, Catia, MicroSolid, etc.
2.2 Parasolid
Parasolid is a geometric modeling kernel originally developed by Shape Data Limited and is now owned by Siemens PLM Software (formerly UGS Corp.), which can be licensed by other companies for their 3D computer graphics software products.
Parasolid’s functions include model creation and editing utilities, such as Boolean modeling operations, feature modeling support, advanced surface design, thickening and hollowing, blending and slicing, and drawing modeling.Parasolid also includes tools for direct model editing, including gradual refinement, offset, geometric replacement, and removal of feature details by automatically regenerating surrounding data.Parasolid also provides extensive graphics and rendering support, including hidden lines, wireframes and drawings, surface subdivision, and model data queries.Major users of the ParaSolid engine include UG, Solidworks, SolidEdge, etc.
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Kernel
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Developer
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Features and Advantages
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Typical Software
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Notes
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ACIS
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Spatial Technology
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Surface modeling; saves computing resources and disk space for relatively simple 3D models
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AutoCAD, CATIA, ProE, ABAQUS, Fluent, Nastran, etc.
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Evolved from surface modeling
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Parasolid
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UGS
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Has advantages for complex models with many facets
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UG, SolidEdge, SolidWorks, ANSYS, Comos, FEMAP, Adams, Adina, etc.
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The most mature and widely used geometric modeling kernel
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2.3 OPENCASCADE
In addition to commercial CAD software, there are also some relatively mature open-source CAD kernels, among which OpenCascade (referred to as OCC) is widely used.
Open CASCADE (referred to as OCC) is an open-source geometric modeling engine. Several CAD/CAE/CAM software have been developed based on this modeling engine, such as FreeCAD and HeeksCAD abroad, and AnyCAD in China. Open CASCADE (referred to as OCC) is a relatively mature modeling engine based on BREP structure in the open-source community, capable of meeting the needs of 2D and 3D solid modeling and surface modeling, and more and more domestic research and usage units are using it. OCC can be divided into three main modules: modeling, visualization, and data management (OCAF). Among them, modeling is the core component; the visualization component is based on OpenGL, which is relatively simple compared to other 3D visualization OpenGL platforms (such as Coin3D, OpenInventor, Ogre3D, OSG, VTK, etc.), and the display effect is relatively poor, unable to fully utilize GPU hardware acceleration; OCAF uses a tree structure to manage data, which is relatively complex, less efficient, and not suitable for custom extensions. Therefore, the use of OCC’s visualization and data management components is not recommended.
3. Available Modeling Kernels
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Platform
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Field
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3D Kernel
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Product
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Company
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Country
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Windows, macOS, Linux, iOS, Android
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CAD, CAM, CAE, AEC
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DGM
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CrownCAD
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Huayun 3D
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China
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Windows
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CAD,CAM,CAE
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CRUX IV
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SINOVATION
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Huatiansoft
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China
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Windows,Linux,
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CAD, CAM, CAE
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Overdrive
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ZWSOFT 3D
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ZWSOFT
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China
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Windows
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CAD, CAM, CAE
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Parasolid & ACIS
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CAXA Solid Design
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Digital Big Square
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China
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Windows,Linux,
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CAD, CAM, CAE, AEC
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C3D
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Kompas-3D
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ASCON Group
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Russia
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Windows
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CAD, AEC
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Open CASCADE
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4MCAD IntelliCAD
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4M S.A
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Greece
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Windows
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MCAD
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ACIS / KCM
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KeyCreator
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Kubotek3D
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USA
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Windows
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AEC
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C3D
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KOMPAS-Builder
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ASCON Group
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Russia
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Windows
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CAD
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C3D + K3 kernel
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K3-Furniture
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Center GeoS
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Russia
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Windows
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AEC
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C3D
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Renga Architecture
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ASCON Group
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Russia
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iPad
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MCAD
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Parasolid
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Shapr3D
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Shapr3D zrt.
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Hungary
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Android
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MCAD
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C3D
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KOMPAS:24
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ASCON Group
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Russia
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Windows
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CAD,BIM
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C3D/ACIS
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NanoCAD
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NanoSoft
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Russia
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Windows
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MCAD
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Parasolid
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T-FLEX
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Top Systems
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Russia
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Windows
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CAM
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C3D
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TECHTRAN
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NIP-Informatic
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Russia
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Windows
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CAD
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C3D
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PASSAT
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NIP-Informatic
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Russia
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Windows, Mac
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CAD, CAM
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Own Kernel
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Rhinoceros 3D
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Robert McNeel and Associates
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USA
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Windows
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CAD
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C3D
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ESPRIT Extra CAD
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LO CNITI, Rubius
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Russia
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Windows
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CAD
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C3D
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BAZIS System
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BAZIS Center
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Russia
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Windows
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CAE
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Parasolid
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Adams
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MSC Software
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USA
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Windows
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CAD, CAM, CAPP
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C3D, ACIS
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ADEM
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ADEM Group
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Russia
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Windows
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CAE
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Parasolid
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ADINA Modeler
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ADINA R&D Inc.
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USA
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Windows
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CAD, AEC, GIS
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ShapeManager
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AutoCAD
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Autodesk
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USA
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Windows
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MCAD
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ShapeManager
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Inventor
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Autodesk
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USA
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Windows, Mac
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MCAD
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ShapeManager
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Fusion360
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Autodesk
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USA
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Windows, Linux, Mac
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MCAD, AEC
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ACIS
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BricsCAD
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Bricsys
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Sweden
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Windows, Mac
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CAD, CAM, CAE
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Parasolid
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Siemens NX
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Siemens PLM Software
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Germany
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Windows
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MCAD
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Parasolid
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SolidFace
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SolidFace
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Brazil
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Windows
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MCAD
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Parasolid, ACIS
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Solid Edge
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Siemens PLM Software
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Germany
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Windows
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MCAD
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Parasolid
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SolidWorks
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Dassault Systèmes
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France
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Windows
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AEC
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Parasolid, ACIS
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MicroStation
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Bentley Systems
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USA
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Windows, Unix
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CAD, CAM, CAE, AEC
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CGM, ACIS
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CATIA
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Dassault Systèmes
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France
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Windows
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Solid Modeler
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GRANITE
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Creo
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Parametric Technology Corporation
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USA
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SaaS
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Solid Modeler
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Parasolid
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Onshape
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PTC
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USA
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Windows, SaaS
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Solid Modeler
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Parasolid, ACIS
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IRONCAD
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Digital Big Square
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China
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Windows
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CAD
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Own Kernel
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Haochen CAD
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Haochen Software
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China
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Windows, Mac
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AEC, BIM
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Own Kernel
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ArchiCAD
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Graphisoft
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Hungary
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Windows
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MCAD
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ACIS
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Cimatron
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3D Systems (Cimatron Ltd.)
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Israel
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Windows
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MCAD
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ACIS
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SpaceClaim
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ANSYS Inc
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USA
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Windows
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MCAD
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European Solid Modeller ESM
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HiCAD
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ISD Group
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Germany
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Mac, Windows
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MCAD
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ACIS
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Cobalt, Xenon, Argon
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Ashlar
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USA
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Windows, Linux
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CAD Optimization
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Own Kernel
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CAESES
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Friendship Systems
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Germany
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Windows, macOS, Linux,
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CAD
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Open Cascade, Coin3D,
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FreeCAD
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FreeCAD
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Windows, macOS, Linux, iOS, Android
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CAD, AEC, BIM
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Geometry Kernel
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IFCEngine, STEPEngine
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RDF
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Bulgarian
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Windows
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BIM
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ACIS
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REVIT
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Autodesk
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USA
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Windows, LINUX
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CAD
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Own Kernel
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CAXA Electronic Drafting Board
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Digital Big Square
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China
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Windows, LINUX
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CAD
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ACIS
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ZWSOFT CAD
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ZWSOFT
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China
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Windows
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CAD,CAM
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Own Kernel, OCC
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JDPaint, ArtForm, SurfMill
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Jingdiao Group
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China
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Windows
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CAM
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OCC
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UltraCAM
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Qianji Intelligent
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China
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4. Future Development Trends
Enhancing Performance. The early design of kernel data structures did not take hardware development into account, defaulting to the single CPU single core design at that time. Now, multi-CPU multi-core, distributed, and GPU computing have matured significantly. Multithreading is already in use, but it is only based on certain interfaces; due to historical reasons, the progress of underlying improvements in both commercial and open-source kernels has been relatively slow. Currently, in addition to industrial design simulation software, many business scenarios have high real-time requirements, which the current geometric kernel still does not meet. Looking at the development of technology in the past decade, compared to the rapid development of artificial intelligence, machine vision, big data, and the internet, the update and development speed of geometric kernels can be considered turtle speed.
Further Lightweight. The intention of Convergent Modeling proposed by PS is to efficiently process 3D printing data, as 3D printing data consists of massive triangular facets, and using pure BREP structure for representation is inefficient. CM addresses this contradiction by simplifying BREP data and operations and integrating facet data. Further simplification or lightweight data structures based on demand, similar to “surgical” precision operations.
BREP Enhancement. BREP is currently the mainstream data structure for 3D geometric kernels, but this does not mean that BREP equals the data structure of 3D geometric kernels. Just as CAD does not equal AutoCAD, CAE does not equal ANSYS. The pros and cons of BREP have been previously described; see in-depth analysis of 3D geometric kernels (3) – basic data structures. BREP cannot express the internal structure of 3D geometry; if BREP is to further refine internal data, it requires splitting the original structure or establishing a virtual topology. Algorithms based on geometric features (such as MAR axial transformation) or technologies similar to volumetric rendering can effectively compensate for this deficiency. In the future, it may be possible to integrate these technologies and methods into the BREP structure to achieve control over 3D solids at smaller dimensions.
Business Integration. The cost-effectiveness of developing general-purpose CAD software using commercial kernels is already very low, and the risks are high unless something innovative can be achieved at the application level. General-purpose 3D geometric kernels provide rich functionality, but the actual usable parts for general simulation software are only a small fraction, leading to low cost-effectiveness. Therefore, in the future, if developing geometric kernels, they can be integrated with business needs to establish more practical kernel structures and functionalities based on business situations. Early CFD preprocessing software is a good example. Because CFD typically needs to process surface data, it does not require a BREP-based structure; general CFD preprocessors will build their own geometric data systems.
Artificial Intelligence. Geometric kernels have certain fixed patterns in topology tracking, feature pattern recognition, object computation, parametric modeling, and constraint solving, where AI can play a role.
References 1. https://zhuanlan.zhihu.com/p/454466612 2. https://www.caxkernel.com/5426.html
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