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{{Short description|Method of CAD drawing file translation}}
'''CAD data exchange''' is a method of [[Engineering drawing|drawing]] [[data exchange]] used to translate between different [[computer-aided design]] ([[Computer-aided design|CAD]]) authoring systems or between CAD and other downstream [[CAx]] systems.<ref name="Schoonmaker2003">{{Cite book|last=Schoonmaker|first=Stephen J.|title=The CAD guidebook : a basic manual for understanding and improving computer-aided design|date=2003|publisher=Marcel Dekker|isbn=0-8247-0871-7|___location=New York|oclc=50868192}}</ref>{{Rp|page=157}}
Many companies use different CAD systems
Since the 1980s, a [[Computer-aided technologies|range of different CAD technologies]] have emerged. They differ in their application aims, user interfaces, performance levels, and in data structures and data file formats.<ref>{{Cite book|title=Product Data Interfaces in CAD/CAM Applications|last=Schuster|first=R.|date=1986-01-01|publisher=Springer Berlin Heidelberg|isbn=978-3-642-82428-9|editor-last=Encarnação|editor-first=Prof Dr-Ing José|series=Symbolic Computation|pages=238–251|language=en|doi=10.1007/978-3-642-82426-5_21|editor-last2=Schuster|editor-first2=Dr-Ing Richard|editor-last3=Vöge|editor-first3=Dr-Ing Ernst|chapter = Progress in the Development of CAD/CAM Interfaces for Transfer of Product Definition Data}}</ref> For interoperability purposes a requirement of accuracy in the data exchange process is of paramount importance and robust exchange mechanisms are needed.<ref name=":05" />
The exchange process targets primarily the geometric information of the CAD data but it can also target other aspects such as [[metadata]], knowledge, manufacturing information, tolerances and assembly structure.▼
▲The exchange process targets primarily the geometric information of the CAD data but it can also target other aspects such as [[metadata]],{{r|Schoonmaker2003|p=153}} knowledge, manufacturing information, tolerances and assembly structure.
There are three options available for CAD data exchange: direct model translation, neutral file exchange and third-party translators.<ref name=":15">Chang, K.-H. (2014). ''Product design modeling using CAD/CAE''. Kidlington, Oxford, UK: Academic Press.</ref>
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== CAD data content ==
Although initially targeted for the geometric information ([[Wire frame model|wire frame]], [[Freeform surface modelling|surfaces]], [[Solid modeling|solids]] and [[drawings]]) of a product, nowadays there are other pieces of information that can be retrieved from a CAD file:<ref name=":05" />
* [[Metadata]] – non-graphical attributes, e.g.:{{r|Schoonmaker2003|p=164}}
** part or detail numbers
** author of the drawing
** revision level, file path on the computer or network storage
** system, the release information, etc.
* Design intent data – e.g. history trees, formulas, rules, guidelines
* Application data – e.g. [[Numerical control|Numerical Control]] tool paths, [[Geometric dimensioning and tolerancing]] ([[GD&T]]), [[process planning]] and [[Bill of materials|assembly structure]]
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== Data exchange options ==
There are at least three ways to exchange data between different CAD system: via a [[Hard copy|hardcopy]] or image (e.g. [[TIFF]], [[GIF]], [[JPEG]], [[BMP file format|BMP]] or [[PCX]], by way of image tracing), CAD-neutral formats or third-party CAD file translators between proprietary file formats.<ref name=":15" />{{r|Schoonmaker2003|p=158}} All have their advantages and disadvantages and may be error-prone.
=== Direct model translation ===
Direct data translators provide a direct solution which entails translating the data stored in a product database directly from one CAD system format to another, usually in one step. There usually exists a neutral database in a direct data translator. The structure of the neutral database must be general, governed by the minimum required definitions of any of the modelling data types, and be independent of any vendor format.<ref name=":05" /> Major CAD systems, such as [[SolidWorks]], [[PTC Creo]], [[Siemens NX]] and [[CATIA]] can directly read and/or write other CAD formats, simply by using ''File Open'' and ''File Save As'' options.<ref name=":15" /> This option is limited by the fact that most CAD formats are proprietary therefore direct translators are typically unidirectional, partially functional and not standardized.<ref>{{Cite
=== Neutral file exchange ===
Neutral file exchange uses an intermediary neutral format to translate data between CAD systems. This method starts from a pre-processor embedded in the original CAD system, which generates the neutral file from the originating CAD format. The target CAD system post-processes the neutral file and converts it into the target native format.<ref>{{cite journal |last1=Choi
==== Neutral formats ====
* [[IGES]] (Initial Graphics Exchange Specification) – originated around the late 1970s and initially published by the American National Standards Institute (ANSI) in 1980 preceding the large-scale deployment of the CAD technology in the industry.<ref>{{Cite journal|last=Björk|first=Bo-Christer|last2=Laakso|first2=Mikael|title=CAD standardisation in the construction industry — A process view|journal=Automation in Construction|volume=19|issue=4|pages=398–406|doi=10.1016/j.autcon.2009.11.010|year=2010}}</ref> This file format considers the product definition as a file of entities, with each entity being represented in an application-independent format.<ref name=":05" /> After the initial release of [[ISO 10303|STEP (ISO 10303)]] in 1994, interest in further development of IGES declined, and Version 5.3 (1996) was the last published standard.<ref name=":15" />▼
▲* [[AutoCAD DXF|DXF]] ([[Drawing Exchange Format|Drawing eXchange Format]]) – developed by [[Autodesk]] in 1982 as their data interoperability solution between [[AutoCAD]] and other CAD systems. The DXF is primarily 2D-based and its format is a tagged data representation of all the information contained in an AutoCAD drawing file, which means that each data element in the file is preceded by an integer number that is called a group code indicating the type of following data element. As most commercial application software developers have chosen to support Autodesk's native [[DWG]] as the format for AutoCAD data interoperability, DXF has become less useful.<ref name=":05" />
▲* [[VDA-FS]] ([[Verband der Automobilindustrie]] – Flächenschnittstelle) – created by the German Association of the Automotive Industry in 1982 as an interoperability method for free-form surfaces.<ref>Product data interfaces in CAD/CAM applications: design, implementation and experiences:Encarnacao, Schuster and Voge, Springer-Verlag, Berlin. 250 pp (250 x 165 mm) (1986) 128 DM. (January 01, 1987). ''Computer-aided Design, 19,'' 3, 158-158.</ref> This format differs from other formats in that it only supports the communication of free-form curve and surface data with associated comments, but no other geometric or non-geometric entities. Therefore, it is limited to representations by parametric [[polynomial]]s, but this covers the great majority of free-form CAD systems. It includes [[Bézier surface|Bézier]], [[B-spline|B-Spline]] and [[Coons patch|Coons]] tensor product types of surfaces and corresponding curves.<ref name=":2">{{Cite book|url=http://link.springer.com/chapter/10.1007/978-3-642-82426-5_13|title=Product Data Interfaces in CAD/CAM Applications|last=Nowacki|first=H.|last2=Dannenberg|first2=L.|date=1986-01-01|publisher=Springer Berlin Heidelberg|isbn=978-3-642-82428-9|editor-last=Encarnação|editor-first=Prof Dr-Ing José|series=Symbolic Computation|pages=150–159|language=en|doi=10.1007/978-3-642-82426-5_13|editor-last2=Schuster|editor-first2=Dr-Ing Richard|editor-last3=Vöge|editor-first3=Dr-Ing Ernst}}</ref> The VDA-FS specification is released in the German Industrial Standard DIN 66301.<ref>{{Cite book|url=http://link.springer.com/chapter/10.1007/978-3-642-82426-5_16|title=Product Data Interfaces in CAD/CAM Applications|last=Phebey|first=T.|date=1986-01-01|publisher=Springer Berlin Heidelberg|isbn=978-3-642-82428-9|editor-last=Encarnação|editor-first=Prof Dr-Ing José|series=Symbolic Computation|pages=176–183|language=en|doi=10.1007/978-3-642-82426-5_16|editor-last2=Schuster|editor-first2=Dr-Ing Richard|editor-last3=Vöge|editor-first3=Dr-Ing Ernst}}</ref>
▲* PDES (Product Data Exchange Specification) – originated in 1988 under the Product Definition Data Interface (PDDI) study done by [[McDonnell Aircraft]] Corporation on behalf of the U.S. Air Force. PDES was designed to completely define a product for all applications over its expected life cycle, including geometry, topology, tolerances, relationships, attributes, and features necessary to completely define a part or assembly of parts. PDES can be viewed as an expansion of IGES where organizational and technological data have been added. In fact, the later PDES contained IGES. The development of PDES under the guidance of the IGES organization and in close collaboration with the [[International Organization for Standardization]] ([[ISO]]) led to the birth of [[Standard for the Exchange of Product model data|STEP]].<ref name=":05" />
▲* [[Standard for the Exchange of Product model data|STEP]] ([[ISO 10303]] – [[Standard for the Exchange of Product model data|STandard for the Exchange of Product model data]]) – the work with the ISO 10303 standard was initiated in 1984 and initially published in 1994, with the objective to standardize the exchange of product data between [[Product Lifecycle Management|PLM]] systems. It is a very comprehensive set of specifications covering many different product types and many life cycle phases. STEP uses the neutral ISO 10303-11 format, also known as an EXPRESS [[Database schema|schema]]. The EXPRESS schema defines not only the data types but also relations and rules applying to them.<ref name=":15" /> STEP supports data exchange, data sharing and data archiving. For data exchange, STEP defines the transitory form of the product data that is to be transferred between a pair of applications. It supports data sharing by providing access to and operation on a single copy of the same product data by more than one application, potentially simultaneously. STEP may also be used to support the development of the archive product data itself.<ref name=":05" /> STEP consists of several hundred documents called [[List of STEP (ISO 10303) parts|parts]]. Every year new parts are added or new revisions of older parts are released. This makes STEP the biggest standard within ISO. The 200-series parts STEP are called Application Protocols (AP),<ref name=":15" /> with the specific parts directly related to CAD systems:
** 203 (Configuration controlled 3D designs of mechanical parts and assemblies) – Mainly used for 3D design and product structure. A subset of AP214 but most widely used.
** 210 (Electronic assembly, interconnect and packaging design) – CAD systems for [[printed circuit board]].
** 212 (Electrotechnical design and installation) – CAD systems for electrical installation and [[cable harness]].
** 214 (Core data for automotive mechanical design processes) – How [[ISO 10303-21|STEP]] is represented in a text file for interchange.
** 238 ([[STEP-NC]] Application interpreted model for computerized numerical controllers) – CAD, [[Computer-aided manufacturing|CAM]], and [[CNC]] machining process information.
** 242 (Managed model based 3D engineering) – the merging of the two leading STEP application protocols, AP 203 and AP 214.
▲
=== Third-party translators ===
Several companies specialize in CAD data translation software that can read from one CAD system and write the information in another CAD system format. There are a handful of companies
Some companies also use these low-level toolkits to create import or export plug-ins for other CAD applications.
====List of software toolkits for developers====
* [https://www.datakit.com/en/crosscad_ware.php Datakit CrossCad/Ware]: SDK to read and write CAD formats.
====List of standalone end-user translation applications====
* [https://www.datakit.com/en/cross_manager.php Datakit CrossManager]: Multi formats CAD translator.
* [https://www.okino.com/ PolyTrans|CAD]: Multi formats CAD translator.
* [http://transmagic.com/ Transmagic]: Multi formats CAD translator.
====List of plug-ins for CAD applications====
* [https://www.datakit.com/en/crosscad_plg.php Datakit CrossCad/Plg]: Import and export plug-ins for Rhino, SOLIDWORKS, ...
* [https://www.okino.com PolyTrans|CAD]: Import/export plug-ins for 3ds Max, Maya, CADMATIC and Visual Components.
* [https://www.npowersoftware.com/NewPowerTranslatorsUniversal.html Power translators]: Import plug-ins for 3dsMax.
== Data exchange quality ==
Data quality can be addressed intrinsically and extrinsically. Intrinsic problems are those related to the CAD model’s structure before any translation process begins, while extrinsic problems relate to those issues appearing during translation. The development of STEP is the best solution to solve the extrinsic problems, extending its current capabilities to support 2-D parametric sections, 3-D parametric assemblies, and history-based modeling. Product data quality is a key issue to avoid intrinsic data exchange problems and simplify the integration of downstream applications in the design chain.
As each CAD system has its own method of describing geometry, both mathematically and structurally, there is always some loss of information when translating data from one CAD data format to another. One example is when the translation occurs between CAD systems using different geometric modeling kernels, in which the translation inconsistencies can lead to anomalies in the data.<ref name=":05" /> The intermediate file formats are also limited in what they can describe, and they can be interpreted differently by both the sending and receiving systems. It is, therefore, important when transferring data between systems to identify what needs to be translated. If only the 3D model is required for the downstream process, then only the model description needs to be transferred. However, there are levels of detail. For example: is the data wireframe, surface, or solid; is the topology ([[Boundary representation|BREP]]) information required; must the face and edge identifications be preserved on subsequent modification; must the feature information and history be preserved between systems; and is [[Product and manufacturing information|PMI]] annotation to be transferred. With product models, retaining the assembly structure may be required.<ref name=":15" /> If drawings need to be translated, the wireframe geometry is normally not an issue; however text, dimensions and other annotation can be an issue, particularly fonts and formats. No matter what data is to be translated, there is also a need to preserve attributes (such as color and layer of graphical objects) and metadata stored within the files.
Some translation methods are more successful than others at translating data between CAD systems. Native formats offer the simple translation of 3D solids, but even so there are few pitfalls to watch out for. If two CAD systems use different representations for one type of geometry at some point the representation must be converted or even discarded, regardless of the type of translation. Modern Neutral formats are designed
Old This is no longer the case with modern standards like STEP AP242, which embeds Validation Properties. Validation Properties are key characteristics of the model (Center of Gravity of a solid, wet area of a surface, PMI characteristics or even check points on a shape), stored by the emitting system and checked by the receiving system. This allows to control the quality of the imported data.
Quality of exchange using STEP is so important that regular benchmarks are run by independent associations (AFNeT, PDES, inc., ProSTEP iViP) to check exchanges between various CAD and PLM systems.
Some CAD systems
▲Some CAD systems has a functionality to compare geometry of two models.<ref>{{cite web|title=Compare Parts and Drawings|url=http://www.solidworks.com/sw/products/3d-cad/compare-parts-drawings.htm}}</ref><ref>{{cite web|last1=Madhavi|first1=Ramesh|title=Comparing Drawings, Models and PCBs with PTC Creo View|url=http://www.ptc.com/cad-software-blog/comparing-drawings-models-and-pcbs-with-ptc-creo-view}}</ref> So, user can compare the model before and after translation from one CAD to another one to estimate quality of the translation, and to fix found defects. But often such functionalities can compare only [[tesselation|tesselations]] of two models. It is really hard algorithmic problem to compare topological elements of two 3D models and restore their associativity to show groups of modified faces, because there are very different representation of geometry data in different CAD systems, but sometimes it is possible. For instance, the component LEDAS Geometry Comparison based on [[C3D]] kernel can be integrated in [[CAD]] system (like [[Autodesk Inventor]], <ref>{{cite web|title=LEDAS Geometry Comparison Licensed for Inventor Plug-in|url=http://www.tenlinks.com/news/ledas-geometry-comparison-licensed-for-inventor-plug-in/|date=Apr 21, 2016}}</ref>) to compare 3D models and pinpoint all of the differences between them.<ref>{{cite web|title=Geometry Comparison from LEDAS now supports all major MCAD formats with DATAKIT libraries|url=http://www.datakit.com/en/news/geometry-comparison-from-ledas-now-supports-all-major-mcad-formats-with-datakit-libraries-137.html|date=February 17, 2015}}</ref>
== MultiCAD Digital Mockups ==
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In a true PLM environment, CAD to CAM data exchange must provide for more than the transfer of geometry. [[Product Manufacturing Information]], whether generated by the designer for use by manufacturing, or generated by the manufacturing organization for use by design, must be a part of the data exchange system. [[STEP-NC]] was designed to carry [[GD&T]] and other PMI through CAD and CAM into a CNC.
== See also ==
* [[Comparison of CAD, CAM, and CAE file viewers]]
== References ==
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