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→Data exchange quality: The study by Prof. Dimitrov is outdated (2011) and does not reflect the state of the art of quality of exchanges using today's standards. So the paragraph was partly rewritten and Validation Properties were introduced. |
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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 have functionalities 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|date=2017-11-27}}</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 [[tessellation]]s 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>
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