Towards long-term archiving of 3D annotated models

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Proceedings of IDMME - Virtual Concept 2010 Bordeaux, France, October 20 – 22, 2010

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Towards long-term archiving of 3D annotated models: a sneak peek to a potential solution Fawzi Kheddouci 1, Louis Rivest 2, Clément Fortin 3 (1) : Department of Automated Production (2) : Department of Automated Production Engineering, Ecole de Technologie Superieure, Engineering, Ecole de Technologie Superieure, 1100 Notre-Dame West, Montreal, Quebec, H3C 1100 Notre-Dame West, Montreal, Quebec, H3C 1K3, Canada. 1K3, Canada. +15144471961/+1 5143968595. +15143968984/+1 5143968595. E-mail : [email protected] E-mail : [email protected] (3) : Department of Mechanical Engineering, Ecole Polytechnique de Montreal, 2500 Chemin de Polytechnique, Montreal, Quebec, H3T 1J4, Canada. +1514 3404711 ext. 4757/+15143405264. E-mail : [email protected]

Abstract: The use of engineering drawings is common practice, in the development of mechanical systems, for product definition capture, exchange and archival purposes. The latter is crucial for the aerospace product development process, characterized by product lifecycles that can exceed 70 years. For many enterprises envisioning the replacement of traditional 2D engineering drawings with 3D annotated CAD models, it becomes necessary to redefine how to maintain product definition data over such a long period of time. This paper discusses the problems associated with the longterm archiving of 3D models annotated with geometric and dimensional tolerances, and other specifications, in light of aerospace requirements that include regulatory and legal aspects. Overviews of the various initiatives as well as possible avenues for solutions are highlighted. A potential archiving solution based on both Acrobat 3D PDF and STEP formats is considered. Key words: Long-term archiving, 3D annotated models, 3D PDF, STEP, CAD. 1- Introduction

product definitions with respect to all of the requirements dictated by the aerospace industry. On the other hand, the archiving solution should be redefined in the context of the development of 3D product definition. Indeed, the elimination of 2D drawings introduces new technical challenges related to data consistency and longevity [D2], due to the obsolescence of storage media and proprietary systems. As part of our work, we only deal with software obsolescence as it refers to the renewal of computer applications, including backup formats. The use of proprietary engineering systems which are embedded in evolving computer platforms makes data conservation more complicated in a long-term perspective. These constraints introduce the notions of integrity and sustainability related to digital archives. The integrity of digital information is characterized either by technical degradation of the logical content (bit sequence) or juridical degradation (where the meaning is altered) [RC1]. Ensuring sustainability entails interpreting the content of information in a meaningful way throughout the retention period. This paper is a part of a research project involving Canadian aerospace industry. The project’s goal is to assess the feasibility of the elimination of engineering drawings from aerospace product development. Two aspects are considered: 1) evaluation of the practice of 3D annotated models within the development product process, and 2) the long-term archiving of 3D annotated models. In this context, we will adopt the 3D annotated model terminology proposed by the SASIG standard [I1] to express “a combination of design model, annotation1 and attributes that describes a product” in compliance with ASME 14.41-

Aerospace companies must ensure the preservation of information resources related to the development of their products, for reuse or further consultation purposes, and also for legal aspects. The collaborative engineering process introduced multiple disciplines and tools, such as CAD and PDM systems, that involve product data composed of CAD and CAM models, 2D drawings, document specifications, finite element analysis models and reports, etc. Engineering drawings are the traditional medium to exchange, distribute and retain product definition information, and serve as lawful proofs. As the transition from traditional 2D drawings to 3D models is increasing, along with the goal of cost reduction [E1], 1 Describes “dimensions, tolerances, notes, text, or symbols” visible industrial players have to define a new way to archive digital without any manual or external manipulation.

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2003 [A2] and ISO 16792 [I2] standards. Our work thus addresses the archiving of 3D mechanical products assuming that product definition is entirely captured with 3D annotated models (no 2D drawings). This paper is organized as follows: First, the long-term archiving of 3D annotated models within the aerospace industry is presented and the requirements are discussed. Next, we describe the initiatives undertaken in the engineering context with respect to archiving. We then propose approaches that are related to the choice of both the repository system and the archiving format adopted in our work. Finally, we propose evaluating Acrobat 3D PDF as a solution to archiving 3D annotated models and give a preliminary conclusion about its feasibility. 2- Long-term archiving of 3D annotated model in the aerospace industry

Long-term archiving is defined as a set of actions carried out, whatever the medium used, to maintain data over a long period of time and to ensure the secured access and readability of information [RC1]. Within the aerospace industry, the challenges of the long-term archiving of 3D models are characterized by the following issues: 1- Data related to aerospace products (aircraft, engines, etc.) have life cycles equal to the product’s lifespan, which may exceed 70 years, such as the famous Boeing B-52 where design studies started in 1945 and which is planned to be in service until 2040 [D1]. 2- Legal requirements involving companies’ responsibilities in providing records, documents, and reports required by regulatory organizations [F1] including specific procedures such as incident investigations during the data retention period. The absence of any of these legal documents can lead, in the worst case, to the immobilization of an entire fleet of aircraft [MP1]. 3- The obsolescence of data representation tools (CAD systems): the life of CAD software is approximately 10 years, and for an operating system it is 18 months [E1], so it seems unlikely that product data will be accessible for over 70 years since the proprietary tool’s applications used to view data will no longer exist, or be accessible. Moreover, all risks associated with the loss of data due to migration processes or system evolutions must be taken into account. Addressing these challenges requires a strategy based on rigorous standardized processes for implementing a robust archiving system that ensures the effective management of information and its evolution, and that also provides sustainable accessibility [L1]. More specifically, it is obligatory to characterize the nature of the information representing the object to be archived (here the 3D annotated model). We also have to clearly identify the information needs of different stakeholders to assess whether they can be satisfied in the context of 3D annotated model conservation. Determining the sustainability criteria that should guide the choice of an archiving solution is also important.

associated with regulatory as well as business obligations. The first type of requirement applies to any digital documents in regards to the choice of an open electronic archiving system. Such a system should be effective enough to ensure the needs of an archival nature, which include preservation of the information’s integrity, accessibility and interoperability, and also various security aspects. The requirements arising from certification regulations stipulate that any aircraft manufacturer must submit its product to the certification process, based on standards of airworthiness. In regards to product conformity, a type certificate is issued by the authority responsible for certification [F2] which certifies that the product is safe to operate within the limits of the category for which it was certified. As part of this process, on a routine basis the certificate holder has to provide the regulatory organization with the digital design data for the validity period of the type certificate. This data is required in order to accomplish activities such as production inspection, surveillance, design review changes, etc. [F3] and sometimes as a part of investigations [F1]. In addition, the need for such data may stem from a legal perspective, in situations such as litigation, mergers and acquisitions of companies or in patent infringement cases [LR1]. Access to archived documents may also serve other objectives that vary according to different stakeholder viewpoints within the product development process. These business needs may lead to various use cases: design re-use (parts used in multiple products), providing lifecycle support (maintenance, spares, recycling and disposal), and within specific procedures such as reverse engineering [LR1]. Finally, a company that implements a quality management system, particularly to certify its suppliers, should ensure the preservation of all of the required documents and its responsibility is to make them available at any time, as in the case, for example, of internal auditing procedures [A3]. Even though engineering drawings meet the various requirements mentioned above, the drawings themselves are not required as such, and any medium that allows access to documents in a clear and unambiguous manner, ensuring the integrity and continuity of information, may be valid. The proposed solution must then be able to provide secured data access to different stakeholders (delegates from regulatory authorities, customers, etc.) including those without the appropriate technology ('low cost' suppliers). More specifically, the certification of 3D annotated models becomes realistic [D2] from the moment they would achieve, as 2D drawings, the objectives of product definition access. It would therefore be possible, as opposed to a scanned 2D drawing, to exploit the model dynamically to manipulate the geometry (views, sections), perform measurements, etc., and access information interactively (tolerances, notes, mechanical properties, etc.). 3- Long-term archiving: State of the art

Among the current efforts, the one most directly relevant for the aviation industry is the LOTAR project [L1], which involves major aerospace companies (Airbus, Boeing, Dassault Aviation, etc.), regulatory organizations (FAA, JAA, etc.) and government agencies (NASA, ESA, NIST, The aerospace industry faces several requirements, generally etc.). The goal of the LOTAR project is to archive CAD and

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PDM (Product Data Management) information with respect to regulatory, legal and business requirements. The project is based on two improved standards: OAIS, a long-term archival system framework, and the STEP (ISO10303) standard as the de facto solution for Product Definition Data. The LOTAR project is working to harmonize other efforts: LTDR, which promotes the use of the STEP standard as a solution for data sharing and retention, and the SAE ARP 9034 [S2] recommendations, in order to produce the NAS/EN 9300 series aerospace standard. Other initiatives, such as the LTA2 in the automotive and MIMER in the military industry, have been inspired from LOTAR’s ongoing achievements. The LTA developed a set of recommendations and best practices for archiving 3D models using the STEP AP214 standard [V2], and MIMER Project [WB1] deployed a solution based on STEP AP239-PLCS (Product LifeCycle Support). The KIM project3, which involves multi-disciplinary companies and academia, recommends the use of lightweight models to support STEP in 3D model preservation. In this context, Patel & Ball [PB1] propose an inventory of the main existing lightweight formats (3DXML, JT, PRC, PLM XML etc.) by evaluating their capabilities in terms of openness, ability to transfer the exact geometry and associated metadata (3D annotations), etc. They indicate that two lightweight formats, JT and PRC, are able to transfer both exact geometry and 3D annotations. The PRC format, which is on track to becoming a standard, is a potential solution. The authors do not, however, detail their evaluations. On the other hand, Hartman & Lim [HL1] compare the functionalities of three lightweight formats (3DXML, JT and U3D), with those of the STEP format, by assessing the conversion of native CAD models (from CATIA and NX). The results indicate that, among the evaluated formats (the three lightweights and STEP) only JT was able to convert 3D annotations. However, the authors do not assess PRC format and its capability to transfer geometry, 3D annotations and related entities. We will thus propose, in this paper, to investigate PRC (3D PDF) format by identifying all the issues related to “3D annotated models” conversion process, especially those concerning 3D annotations transfer. As this latter can be problematic, due to the heterogeneity of the tools used by CAD software to generate those non geometrical entities [T1], we think that the proposed solution (converting the native model to STEP and then to PRC format) will guarantee the preservation of both exact geometry and 3D annotations.

The preservation techniques of digital data include three main strategies: information migration, technology emulation and encapsulation [LS1]. Data migration is intended to periodically perform the transfer of digital data associated with a computer application or a medium from an old to a new version. This type of practice, rather appropriate for the short term, leads to risks related to the degradation of information during the transfer, as evidenced by the problems associated with the conversion of 3D models (from CATIA V4 to V5) in the development of the Airbus A380 [M2], accentuated by proprietary software dependency. The goal of emulation is to overcome the problem of successive migrations by transposing the original environment onto a present or future software platform. This strategy, as opposed to migration, aims to store information in its native form, by reproducing the look and feel of the software or associated computer system [LS1]. The technique offers potential for the long term but remains expensive [PB1], and its main disadvantage is the complexity of its implementation, because of the type of data to be retained (executable files) [LS1] and the protection mechanisms imposed by CAD software vendors [S1]. Despite the existence of emulation platforms such VMWare4, QEMU5, and Xen6, which can reproduce the environment of old CAD software (CATIA V4), the approach is not yet mature enough [S1]. The purpose of encapsulation is to address issues related to technological obsolescence, and thus software and system dependencies. This is made possible by the inclusion of digital archived information and associated information (metadata) in a logical container, along with all the documentation and specifications related to the archiving format required to interpret it, whatever the consequences of technological changes. Although not yet in practice for the archiving of 3D models, this approach is the subject of research projects in the domain of digital archives [Z1]. Its main drawback is the complexity of monitoring updates for all the encapsulated information, including the technology used and the changing needs of the user community [M1].

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4.2 – Archiving system

All of the projects mentioned above converge towards the hypothesis that the conceptual architecture of an archiving electronic system, targeting long-term archiving, must be based on a robust model developed in an open framework. It should be independent of external systems and flexible to future evolutions. The choice of the OAIS reference model, which relies primarily on the encapsulation approach 4- Alternative solutions and proposed approach combined with specific processes of migration, is In this section we give an overview about the existing technical recommended [L1]. approaches related to digital data archiving. We also introduce The Open Archival Information System is a conceptual the OAIS as a potential long-term archiving system and model for the development of a digital archiving system. It propose archiving solutions to 3D annotated models. was developed in 2002 by the Consultative Committee for Space Data Systems (CCSDS), which subsequently became an international standard (ISO 14721) [I4]. It is an 4.1 – Digital preservation techniques architectural model that serves as a framework to define an

Long-Term Archiving (LTA) of digital Product Data, which are not based on technical drawings[V1]. 3 Knowledge Information Management [BP1]

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archiving system. It defines the problems and needs, and identifies the processes and the flow of information exchanged within the system, as well as the roles of stakeholders, etc. The recommendations of the OAIS are primarily the satisfaction of the requirements of an archival nature, including interoperability, integrity checks and authenticity, access controls and the creation of log files [L2]. Recently, Dassault Aviations chose the DIAS PLM solution (Digital Information Archiving System, Product Lifecycle Management), an OAISbased model, as the official system for archiving their 3D digital models within the Falcon X7 development project [BN1]. 4.3 – Proposed archiving solution

The satisfaction of various obligations and data usage scenarios (visualization, inspection, reuse or for a product’s update), including those related to future needs, require clear and unambiguous interpretations of 3D models and any other necessary information to complete the product definition. The minimum requirement is to make available the nominal geometry, expressed through the boundary representation (BRep) of the 3D model to interpret the dimensions, display the views, visualize sections, etc., and also to read the 3D geometric and dimensional tolerances and other notes[V2] as required by ISO 16792 / ASME Y14.41-2003. Preserving the B-Rep allows the exploitation of a 3D model independently of its program application (CAD system) in any version. Two main aspects are to be considered in the choice of a 3D annotated model archiving solution: data integrity, which deals with the way the 3D model content is preserved; and data sustainability, which deals with how the data is maintained for the lifespan of the data storage. For this purpose, the American Library of Congress has defined a set of sustainability factors that must be considered when choosing a long-term archiving format, which are mainly: Openness, adoption, selfdocumentation, and security mechanisms [AF1]. Openness is characterized by the choice of non-proprietary, open standards along with the availability of complete format specifications. Adoption refers to the degree to which the format is widely used, and self-documentation deals with the ability to support descriptive metadata over the archiving period. Security mechanisms refer to the availability of format access protection tools. From the archival perspective, the simplicity of use and reduced file size are also aspects to consider in choosing a solution [H1]. Three alternatives should be considered for this purpose: native CAD, neutral or lightweight formats. Both neutral (STEP, IGES) and lightweight (3DXML, JT, PRC, etc.) formats are potential solutions. The native CAD formats are discarded due to their obsolescence and vendor dependency, which are not in line with the sustainability criteria described above. The STEP standard (ISO 10303) has become a reference in CAD/CAM data exchange. It represents a valid alternative for long-term archiving particularly with the recent deployment of the application protocol AP203 e2 [I3], which supports 3D annotations as required by ASME Y14.41-2003. Nevertheless, STEP models are still heavy-weight and they do not provide security mechanisms [DD1]. On the other hand, the lightweight formats, widely used in data

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collaboration, are a serious alternative to long-term archiving due to their reduced volume, simplicity of use, ease of remote access, etc. [DD1]. Among the available solutions, the PRC format offers interesting capabilities in terms of openness (its specifications are freely available and is currently under standardization process, initiated by ISO and Boeing [A1, I5]), B-Rep and 3D annotation support, as well as security and data compression aspects [PB1]. The PRC format7 represents a potential 3D annotated models archiving solution. It is embedded in the Acrobat 3D PDF software application and is used within the CAD model conversion process to transfer features such as: exact geometry, annotations, annotated views and references, etc. It will be evaluated in the next section. 5- Evaluation of the conversion of 3D annotated models to Acrobat 3D PDF

The evaluation is based on a sample of 3D annotated models obtained from an aerospace project partner. The CAD models were generated in CATIA V5R17 SP6 using the FT&A module to incorporate 3D annotations. The objective is to archive 3D annotated models by preserving B-Rep and 3D annotations within the conversion process. We perform the transfer from CATIA V5 (native model) to 3D PDF (archived model) using Acrobat Pro Extended V9 solution by selecting the PRC format, and then evaluate the possible degradation. The evaluation consists of two main aspects: the solid geometry transfer degradation and the 3D annotations (including annotated views and captures) transfer integrity. To evaluate the geometry degradation between the 3D native model and the archived model, the 3DComparator solution [MM1], developed within the Products, Processes and Systems Engineering Laboratory at the Ecole de Technologie Superieure, was used. This comparator is capable of identifying the zones where the geometry is dissimilar between two models. To verify the 3D annotations, and related geometry integrity, all entities were counted both in the CATIA V5 model and in the converted lightweight model. The graphical integrity of annotations was also examined. Figure 1 illustrates an example of a 3D annotated view extracted from one of the CATIA V5 models.

Figure1: Example of a 3D annotated view

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The evaluation results indicate that during the conversion process there is no geometry degradation and that all 3D annotations, views and captures are successfully preserved. In addition, on average, a 65% file size reduction was obtained. However, one issue regarding the display of 3D annotations was observed within the 3D PDF model. Compared to the previous annotated view (figure 1), an overlapping display problem of 3D annotations was found (shown in figure 2). The FT&A8 module allows the scale assigned to each annotated view to be changed in order to avoid overloading the display, which makes some 3D annotations unreadable. In Acrobat Pro Extended it is impossible to edit the view scale, which is set to 1:1.

Figure 3 illustrates the result of importing a STEP model (exported from CATIA) to Acrobat 3D, based on the previous annotated view (figure 1). The overlapping problem was resolved. This can be explained by a STEP translator capability that supports the polyline representation at both STEP import and export, while 3D PDF support it within STEP rather than CATIA V5 import processes. As a result, the proposed conversion process (CATIA V5 to STEP and then to 3D PDF) could be considered as a potential solution to resolve the 3D annotations display issues.

Figure 3: 3D annotations display issue resolved on the 3D PDF with STEP import process Figure 2: 3D annotations display issue on the 3D PDF

We also observed that modifying the scale of the annotation font (text, symbol, etc.) within the FT&A module has no effect because of font incompatibility between CATIA V5 and Adobe due to their proprietary nature. The proposed alternative is to map the source font to a standard text font (such as UNICODE) to ensure font independency and thus maintain its graphical representation whatever the target system. The CAx Implementor Forum9, which aims to accelerate the development of STEP translator resources, is examining this issue. The working group is currently developing mechanisms based on the polyline approach. The objective of this technique is to transform the extracted annotation from the source CAD system and store it in a STEP model as a graphical representation of data (lines, arcs, etc.). A possible solution path, which requires a specific setup, is implemented on CATIA V5R19. This procedure is described by the following steps [MC1]: - Creating a CATIA V5 variable environment CATDXActive3DAnnotation and assigning it the value 1. This will make the "3D annotations" functionality visible, which can be found in the CATIA Options menu, within the Compatibility submenu at the STEP tab; - Activating this functionality; and - Selecting the application protocol STEP AP 203 e2. It is therefore possible to convert the native CATIA model to STEP in order to recover the original layout of 3D annotations.

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6- Conclusion

The problem of long-term archiving in the aerospace industry involves addressing product data definition retention over a long period (more than 70 years) as well as various requirements (including regulatory) responsible for setting the legal framework. These obligations require digital type design accessibility and intelligibility of both technical and legal contents. Solutions must necessarily be based on standards, such as the OAIS model as an archiving system, including the choice of a 3D annotated model archiving format. This paper envisions 3D PDF as a long-term archiving solution because it meets the durability criteria that are necessary to maintain 3D annotated models. The partial tests reported here indicate that the solution can satisfy the integrity requirements: the exact B-Rep geometry is preserved when converting native CATIA V5 models to 3D PDF PRC format. However, issues associated with 3D annotation display arise when converting from CATIA V5 to 3D PDF, issues which can be resolved by converting from CATIA V5 to STEP format first, and then to 3D PDF format. 7- References

[A1] AIIM, Association for Information and Image Management. AIIM Partners with Industry Leaders to Advance PRC 3D File Format. En ligne, 2009. [A2] ASME, American Society of Mechanical Engineers. 2003. Digital product definition data practices. ASME Y14.41-2003. New York: American Society of Mechanical

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Engineers, 91 p. [A3] AS 9100 SAE, Quality management systems, aerospace, requirements. 2004, Society of Automotive Engineers: Warrendale, Penns. p. 39. [AF1] Arms, C., Fleischhauer C. Digital formats: Factors for sustainability, functionality, and quality. In Office of Strategic Initiatives, Library of Congress, 17, 2003. [BN1] Bignand I., Nuwendam F., Fouache M., Archivage numérique à long terme : l'exemple du Falcon 7X. Association des archivistes français, 2010. [BP1] Ball, A., Patel M., McMahon C., Green S., Clarkson J. and Culley S. A grand challenge: immortal information and through-life knowledge management (KIM). In International Journal of Digital Curation, 1(1), 2008. [D1] Defense Science Board Washington DC. Defense Science Board Task Force on B-52H Re-Engining. En ligne, Defense Technical Information Center, 2004. [D2] DeLaPorte, J. Data Consistency, Interoperability, and Longevity for FAA Certification of 3D MBD Systems. COE 2009 Annual PLM Conference & Technifair, Seattle,Washington, Avril 19-22, 2009. [DD1] Ding, L., Davies D. and McMahon C. The integration of lightweight representation and annotation for collaborative design representation. In Proceedings of the Research in Engineering Design (2009). [E1] Engineering Data Interoperability Working Group . Aerospace Industry Guidelines for Implementing Interoperability Standards for Engineering Data. Aerospace Industries Association, Inc, 2009. [F1] FAA, Federal Aviation Administration. Investigative and enforcement procedures. U.S. Department Of Transportation, Federal Aviation Administration, 1979. [F2] FAA, Federal Aviation Administration . Certification procedures for products and parts--Type Certificates : Type certificate. U.S. Department Of Transportation, 1965. [F3] FAA, Federal Aviation Administration. Type Certification U.S. Department Of Transportation, Federal Aviation Administration, 2007. [H1] Huc, C. Quels criteres applicables aux formats pour la perennisation? In Presentation du Groupe PIN, jan, 2003. [HL1] Hartman N., Lim.A. Examining Neutral Formats for Visualization and Data Exchange. In Proceedings of the International Conference on Engineering & Technology: Globalization of Technology (Nashville, TN, USA, Nov 2008). [I1] ISO, Organisation Internationale de Normalisation. 2006. SASIG product data quality guidelines for the global automotive industry. Stategic Automotive product data Standards Industry Group, ISO 26183:2006. 198 p. [I2] ISO, Organisation Internationale de Normalisation. 2006. Documentation technique de produits -- Données de définition d'un produit. ISO 16792:2006. Genève, Suisse. [I3] ISO, Organisation Internationale de Normalisation. 2005. Systèmes d'automatisation industrielle et intégration -Représentation et échange de données de produits -- Partie 203: Protocole d'application: Conceptions 3D contrôlées de configuration de pièces mécaniques et des assemblages. ISO 10303-203:2005. Genève, Suisse. [I4] ISO, Organisation Internationale de Normalisation. 2003. Systèmes de transfert des informations et données spatiales.

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