A CASE STUDY ON THE USE OF DESIGN EXEMPLAR AS A SEARCH AND RETRIEVAL TOOL

This thesis presents a case study examining the suitability of design exemplar technology as a CAD query tool for an industrial scenario. The search and retrieval of geometrically similar mold inserts to save tooling cost for a tire manufacturing company is taken as the case study. During the implementation of the design exemplar as a CAD search and retrieval tool, several limitations of it are identified, such as the difficulty and tediousness in authoring exemplars for real world problems. To overcome these limitations, a new mathematical-based exemplar approach (mathematical model) is developed for tire mold insert retrieval. This approach calculates a set of maxima and minima based on the specifications of the target mold insert and identifies similar molds that fall within these specifications. Though the mathematical model requires less effort to author the exemplar queries than the initial boundary envelope approach, it has an unreasonably high time complexity when implemented using design exemplar. A partially developed mathematical-based exemplar takes 30 seconds to run through a sample database of 10 mold inserts. Assuming that a fully built exemplar would take more time when run on a database of 7,000 mold inserts as it would have more number of constraints added to it, the approach was not implemented through design exemplar tool. However, as this exemplar approach gives a satisfactory theoretical solution to the problem, the exemplar is hard-coded in an independent C++ program to suit the requirements at hand. The mathematical-model which is implemented in an independent C++ program successfully searches through the complete database of 7,000 tire mold inserts, retrieving similar mold inserts, in a span of one second, a huge efficiency gain when compared with the traditional exemplar system. Apart from the time reduction for the search and retrieval, the exemplar inspired program has an additional advantage in that no geometrical entities must be handled to build exemplars. However, the mathematical model may result in several false positives that must be manually eliminated. In an experiment, 15 mold inserts were randomly selected from the database and were searched for similar mold inserts using the program developed. In the experiment, it was observed that there were no false negatives and the number of false positive ranged from 0 - 10 among the 11 retrieved mold inserts. Considering the size of the database which is roughly 7000 mold inserts, the mathematical still provides advantages in search and retrieval. It is still good because 7,000 have been reduced on an average to 11. During the experiment, it as been found that 80 percent of the mold inserts which were tested have similar mold inserts. The design exemplar tool could have helped company to save the tooling cost of $184,000 per annum by providing them with a search and retrieval tool. However, it was not implemented because of some of the limitations mentioned above. Still the strategies of design exemplar are valid for querying CAD models. This is proved by the fact that the mathematical model which is an essentially an exemplar can successfully finds and retrieves similar mold inserts

Efficient Point-Cloud Processing with Primitive Shapes

This thesis presents methods for efficient processing of point-clouds based on primitive shapes. The set of considered simple parametric shapes consists of planes, spheres, cylinders, cones and tori. The algorithms developed in this work are targeted at scenarios in which the occurring surfaces can be well represented by this set of shape primitives which is the case in many man-made environments such as e.g. industrial compounds, cities or building interiors. A primitive subsumes a set of corresponding points in the point-cloud and serves as a proxy for them. Therefore primitives are well suited to directly address the unavoidable oversampling of large point-clouds and lay the foundation for efficient point-cloud processing algorithms. The first contribution of this thesis is a novel shape primitive detection method that is efficient even on very large and noisy point-clouds. Several applications for the detected primitives are subsequently explored, resulting in a set of novel algorithms for primitive-based point-cloud processing in the areas of compression, recognition and completion. Each of these application directly exploits and benefits from one or more of the detected primitives' properties such as approximation, abstraction, segmentation and continuability

Shape Retrieval Methods for Architectural 3D Models

This thesis introduces new methods for content-based retrieval of architecture-related 3D models. We thereby consider two different overall types of architectural 3D models. The first type consists of context objects that are used for detailed design and decoration of 3D building model drafts. This includes e.g. furnishing for interior design or barriers and fences for forming the exterior environment. The second type consists of actual building models. To enable efficient content-based retrieval for both model types that is tailored to the user requirements of the architectural domain, type-specific algorithms must be developed. On the one hand, context objects like furnishing that provide similar functions (e.g. seating furniture) often share a similar shape. Nevertheless they might be considered to belong to different object classes from an architectural point of view (e.g. armchair, elbow chair, swivel chair). The differentiation is due to small geometric details and is sometimes only obvious to an expert from the domain. Building models on the other hand are often distinguished according to the underlying floor- and room plans. Topological floor plan properties for example serve as a starting point for telling apart residential and commercial buildings. The first contribution of this thesis is a new meta descriptor for 3D retrieval that combines different types of local shape descriptors using a supervised learning approach. The approach enables the differentiation of object classes according to small geometric details and at the same time integrates expert knowledge from the field of architecture. We evaluate our approach using a database containing arbitrary 3D models as well as on one that only consists of models from the architectural domain. We then further extend our approach by adding a sophisticated shape descriptor localization strategy. Additionally, we exploit knowledge about the spatial relationship of object components to further enhance the retrieval performance. In the second part of the thesis we introduce attributed room connectivity graphs (RCGs) as a means to characterize a 3D building model according to the structure of its underlying floor plans. We first describe how RCGs are inferred from a given building model and discuss how substructures of this graph can be queried efficiently. We then introduce a new descriptor denoted as Bag-of-Attributed-Subgraphs that transforms attributed graphs into a vector-based representation using subgraph embeddings. We finally evaluate the retrieval performance of this new method on a database consisting of building models with different floor plan types. All methods presented in this thesis are aimed at an as automated as possible workflow for indexing and retrieval such that only minimum human interaction is required. Accordingly, only polygon soups are required as inputs which do not need to be manually repaired or structured. Human effort is only needed for offline groundtruth generation to enable supervised learning and for providing information about the orientation of building models and the unit of measurement used for modeling

Management and Visualisation of Non-linear History of Polygonal 3D Models

The research presented in this thesis concerns the problems of maintenance and revision control of large-scale three dimensional (3D) models over the Internet. As the models grow in size and the authoring tools grow in complexity, standard approaches to collaborative asset development become impractical. The prevalent paradigm of sharing files on a file system poses serious risks with regards, but not limited to, ensuring consistency and concurrency of multi-user 3D editing. Although modifications might be tracked manually using naming conventions or automatically in a version control system (VCS), understanding the provenance of a large 3D dataset is hard due to revision metadata not being associated with the underlying scene structures. Some tools and protocols enable seamless synchronisation of file and directory changes in remote locations. However, the existing web-based technologies are not yet fully exploiting the modern design patters for access to and management of alternative shared resources online. Therefore, four distinct but highly interconnected conceptual tools are explored. The first is the organisation of 3D assets within recent document-oriented No Structured Query Language (NoSQL) databases. These "schemaless" databases, unlike their relational counterparts, do not represent data in rigid table structures. Instead, they rely on polymorphic documents composed of key-value pairs that are much better suited to the diverse nature of 3D assets. Hence, a domain-specific non-linear revision control system 3D Repo is built around a NoSQL database to enable asynchronous editing similar to traditional VCSs. The second concept is that of visual 3D differencing and merging. The accompanying 3D Diff tool supports interactive conflict resolution at the level of scene graph nodes that are de facto the delta changes stored in the repository. The third is the utilisation of HyperText Transfer Protocol (HTTP) for the purposes of 3D data management. The XML3DRepo daemon application exposes the contents of the repository and the version control logic in a Representational State Transfer (REST) style of architecture. At the same time, it manifests the effects of various 3D encoding strategies on the file sizes and download times in modern web browsers. The fourth and final concept is the reverse-engineering of an editing history. Even if the models are being version controlled, the extracted provenance is limited to additions, deletions and modifications. The 3D Timeline tool, therefore, implies a plausible history of common modelling operations such as duplications, transformations, etc. Given a collection of 3D models, it estimates a part-based correspondence and visualises it in a temporal flow. The prototype tools developed as part of the research were evaluated in pilot user studies that suggest they are usable by the end users and well suited to their respective tasks. Together, the results constitute a novel framework that demonstrates the feasibility of a domain-specific 3D version control

A feature-based shape similarity assessment framework

The popularity of 3D CAD systems is resulting in a large number of CAD models being generated. Availability of these CAD models is opening up new ways in which information can be archived, analyzed, and reused. 3D geometric information is one of the main components of CAD models. Therefore shape similarity assessment is a fundamental geometric reasoning problem that finds several different applications. In many design and manufacturing applications, the gross shape of the 3D parts does not play an important role in the similarity assessment. Instead certain attributes of part features play a dominant role in determining the similarity between two parts. Different feature-based models are usually created using their own coordinate systems. Therefore, feature-based shape similarity assessment involves finding the optimal alignment transformations for two sets of feature vectors. The optimal alignment corresponds to the minimum value of a distance function that is computed between the two sets of feature vectors being aligned. In order to compute the distance function the closest neighbor to each feature vector needs to be identified. We have developed optimal feature alignment algorithms based on the partitioning of the transformation space into regions such that the closest neighbors are invariant within each region. These algorithms can work with customizable distance functions. We have shown that they have polynomial time complexity. For higher dimension transformation spaces it is harder to design algorithms based on the partitioning of transformation spaces because the data structures involved are very complex. In those cases, feature alignment algorithms based on iterative strategies have been developed. Iterative strategies make use of optimal feature alignment algorithms based on the partitioning of lower dimension transformation spaces. Extensive experiments have been carried out to provide empirical evidence that iterative strategies can find the optimal solution for feature alignment problems. A feature-based shape similarity analysis framework has been built based on the feature alignment algorithms. This framework has been demonstrated with the two following applications. A machining feature based alignment algorithm has been developed to automatically search databases for parts that are similar to a newly designed part in terms of machining features. We expect that the retrieved parts can be used as a basis to perform cost estimation of the newly designed part. A surface feature based alignment algorithm has been developed to automatically search databases for parts that are similar to a newly designed part in terms of surface features. We expect that the retrieved parts can be used as a basis to choose the most appropriate tool maker for the newly designed part. We believe that the feature-based shape similarity assessment algorithms developed in this thesis will provide the foundations for designing new feature-based shape similarity algorithms that will enable designers to efficiently retrieve archived geometric information. We expect that these tools will facilitate information reuse and therefore decrease product development time and cost

Facet-based Indexing of Multiple Artifacts - A Framework to Cope with Vague Search Requests in the Domain of Product Development

Durch den zunehmenden Einsatz von Informations- und Kommunikationstechnologien sowie den schnellen Technologiefortschritt steht die Entwicklung technischer Produkte vor immer neuen Herausforderungen. Dabei ist die Aufgabe der Produktentwicklung selbst als Problemlösungsprozess zu betrachten, in dem Lösungen mittels intensiver Informationsverarbeitung gefunden werden. Somit werden täglich unterschiedlichste Arten von Informationen erstellt, benötigt und verarbeitet, die primär in digitaler Form vorliegen. Diese werden in heterogenen Anwendungssystemen verwaltet, was eine Wiederverwendung bereits existierender Informationen erschwert. Damit beansprucht die Suche nach Informationen noch immer einen erheblichen Anteil der Entwicklungszeit. Zur Verbesserung der Informationsversorgung im Bereich der technischen Produktentwicklung wird ein interaktives Information Retrieval-System – das LFRP-Framework – vorgestellt. Dieses kombiniert die vier Basiskonzepte der multiplen Ebenen, der facettierten Suche, des Rankings und der parallelen Koordinaten, um hochkomplexe Informationsbedürfnisse zu befriedigen. Seine Realisierung erfordert neben einer geeigneten Suchoberfläche die Entwicklung einer Indexierungskomponente, welche die vorhandenen Informationen in eine für das LFRP-Framework rechnerverarbeitbare Form transformiert. Dieser als Indexierung bezeichnete Prozess stellt die Grundvoraussetzung für die Funktionsfähigkeit eines Suchsystems dar und liegt daher im Fokus der Betrachtung. Es wird ein Lösungsansatz vorgestellt, welcher eine Indexierung in Form facettenbasierter Suchkriterien ermöglicht und dabei nicht nur Informationen aus heterogenen Anwendungssystemen, sondern insbesondere aus entwicklungsspezifischen Dokumenten, wie CAD-Modellen, technischen Zeichnungen oder Stücklisten, berücksichtigt.Due to both the increasing use of information and communication technology as well as the fast technological progress the domain of product development has to face new challenges. Thereby, the task of developing products is a problem solving process itself and requires intensive information processing activities in order to find appropriate solutions. Thus, a variety of information is generated, needed and processed every day. Mostly available in digital form, this data is archived in heterogenous application systems. This makes it difficult to re-use already existing data. Consequently, a significant part of the development time is still affected by searching for information. In order to improve the supply of data and information in the domain of product development an interactive information retrieval system – the LFRP framework – is proposed. This framework combines four core concepts – multiple layers, facetted search, ranking, and parallel coordinates – to satisfy information needs of high complexity. Besides an appropriate search interface, realizing this framework necessitates an indexing component, too. This component is the prerequisite for operating a search system and therefore presents the main issue of this work. The proposed approach enables an indexing process by using facetted search criteria. For this purpose, data provided not only by heterogenous application systems but also by documents characteristic for the development of products such as CAD models, technical drawings, or bills of materials is considered