Parametric exchange of round shapes between a mechanical CAD system and a ship CAD system

Interoperability among heterogeneous Computed-Aided Design (CAD) systems is an important issue. With the advent of global outsourcing, collaborative design has expanded from inside the enterprise to parts suppliers. This paper introduces a method for design data exchange between shipyards and equipment suppliers. These parties usually use different CAD systems, because they want to select the most suitable one for their jobs. CAD systems provide modeling functionality that is based on distinct modeling units. Therefore, to exchange design data, one must map between these two distinct sets of modeling units. Some modeling units can be directly mapped and converted, and other modeling units that cannot be directly mapped (such as the fillet feature in a mechanical CAD system) are converted by the indirect mapping procedure proposed in this paper. The proposed method is demonstrated with case studies between TransCAD and the AVEVA Marine system.     

Mapping 2D midship drawings into a 3D ship hull model based on STEP AP218

Standard for the exchange of product model data (STEP) AP218 has a standard schema to represent the structural model of a midship section. While its schema facilitate the exchange of ship structural models among heterogeneous systems, most shipyards and classification societies exchange information using 2D paper drawings. We propose a feature parameter input method to generate a 3D STEP model of a ship structure from 2D drawings. We have analyzed the ship structure information contained in 2D drawings and have defined a data model to express the contents of the drawing. We also developed a GUI for the feature parameter input. To translate 2D information extracted from the drawing into a STEP AP218 model, we have developed a shape generation library and have generated the 3D ship model through this library. The generated 3D STEP model of a ship structure can be used to exchange information between design departments in a shipyard as well as between classification societies and shipyards.     

CAD mesh model simplification with assembly features preservation

This paper aims to investigate a CAD mesh model simplification method with assembly features preservation, in order to satisfy the requirement of assembly field for the information of 3D model. The proposed method simplifies a CAD mesh model as follows. Firstly, the notion of ＂conjugation＂ is incorporated into the definition of assembly features, with the purpose of benefitting the downstream applications such as assembly features recognition and preservation. Subsequently, the attributed adjacency graphs （AAGs） of the region- level-represented parts are established. The assembly features are automatically recognized by searching for conjugated subgraphs of every two AAGs based on subgraph isomorphism algorithm. In order to improve the efficiency of assembly features recognition, the characteristics of conjugated subgraphs are adopted to initialize the mapping matrix, and the ＂verifying while matching strategy＂ is used to verify the validity of every two newly founded vertices which are correspondingly matched. Then, simplified CAD mesh model with assembly features preserved is constructed after suppressing the common form features. The method is applied successfully to simplify the CAD mesh model with assembly features well preserved. Moreover, the tradeoff between the cost of time for conjugated subgraphs matching and the complexity of the to-be-matched parts is proven to be almost linear.     

Finally Everyone Can Work With Highly Complex 3D Models

In the past, access to 3D databases was restricted to few specialists having the appropriate CAD skills, software, and graphics hardware. The availability of inexpensive graphics support on personal computers, the Internet’s impact on private and commercial communication, and the emergence of multimedia standards provide the basis for linking CAD databases with other personal productivity and communication tools and for making them accessible to everyone at home, in schools, in hospitals, or in the industry. For example, employees that have no design expertise, customers, and suppliers would benefit from having an easy access to the 3D databases of a company for: collaborative design review, 3D-based multi-media problem reports, collaborative problem solving and tracking, online training and documentation, internet-based part purchasing and subcontracting, demonstration to customers, or advertising. This presentation will address three of the key issues that have so far limited the non-specialist’s access to 3D databases. First-time or occasional non-expert users need to become instant experts in 3D navigation through Virtual Environments or in the interactive manipulation of digital 3D models, so that they may immediately focus on their tasks, and not waste precious time learning and fighting an unnatural user interface. Immersive VR is not the panacea – other more effective techniques show promise. The data complexity found in commercial CAD databases, especially in the automotive, aerospace, and construction industries, significantly exceeds the capabilities of any interactive graphics system. This situation is not likely to change, since the growth of the complexity and availability of 3D models outpaces the performance improvement of personal computers. Research on the automatic simplification of 3D models and on the use of levels of detail to accelerate the rendering of distant portions of the scene is growing rapidly. The still limited bandwidth of internet communication channels prohibits a pervasive access to large amounts of 3D data. Recent 3D compression techniques reduce the storage requirements for polyhedral 3D models by two orders of magnitudes.     

Finally Everyone Can Work With Highly Complex 3D Models

In the past, access to 3D databases was restricted to few specialists having the appropriate CAD skills, software, and graphics hardware. The availability of inexpensive graphics support on personal computers, the Internet’s impact on private and commercial communication, and the emergence of multimedia standards provide the basis for linking CAD databases with other personal productivity and communication tools and for making them accessible to everyone at home, in schools, in hospitals, or in the industry. For example, employees that have no design expertise, customers, and suppliers would benefit from having an easy access to the 3D databases of a company for: collaborative design review, 3D-based multi-media problem reports, collaborative problem solving and tracking, online training and documentation, internet-based part purchasing and subcontracting, demonstration to customers, or advertising. This presentation will address three of the key issues that have so far limited the non-specialist’s access to 3D databases. First-time or occasional non-expert users need to become instant experts in 3D navigation through Virtual Environments or in the interactive manipulation of digital 3D models, so that they may immediately focus on their tasks, and not waste precious time learning and fighting an unnatural user interface. Immersive VR is not the panacea – other more effective techniques show promise. The data complexity found in commercial CAD databases, especially in the automotive, aerospace, and construction industries, significantly exceeds the capabilities of any interactive graphics system. This situation is not likely to change, since the growth of the complexity and availability of 3D models outpaces the performance improvement of personal computers. Research on the automatic simplification of 3D models and on the use of levels of detail to accelerate the rendering of distant portions of the scene is growing rapidly. The still limited bandwidth of internet communication channels prohibits a pervasive access to large amounts of 3D data. Recent 3D compression techniques reduce the storage requirements for polyhedral 3D models by two orders of magnitudes.     

Multi-agent collaborative 3D design with geometric model at different levels of detail

This paper presents a scheme for collaborative 3D design using product model at various levels of detail (LODs). Design features are selectively hidden at each level from certain participants, depending on their actual needs and individual accessibility in the collaboration. A tree data structure represents the feature hierarchy of CAD construction, the link between feature and LOD, and 2D mesh data for display control of each feature. An XML/XSLT-based approach is proposed to enable real-time visualization of different LOD models in distributed environment. A collaborative design system is implemented using multi-agent technologies, which focuses on function design of each agent, interactions among agents, the client–server structure, and generation of the LOD data using the XML/XSLT approach. A scenario of synchronous 3D mold assembly demonstrates that geometric categorization of product model provides an operational mechanism for assuring security of information sharing in engineering collaborations over the Internet. It also validates the effectiveness of the agent technologies for automating complex engineering activities.     

面向装配的飞行器超大模型实时可视化技术

针对飞行器大数据量CAD模型实时绘制困难的问题,提出一种LOD自动批处理生成以及实时自适应绘制方法.以零部件为处理对象以保留装配树信息,结合模型分割完成超大模型简化,并根据计算机存储能力、实时绘制能力以及CAD模型特点,实现了定量的LOD自动批处理生成;以精确遮罩查询为基础,根据计算机实时绘制负载和CAD模型面片密度,动态地调整LOD精度等级,使得各个模型的精度基本一致,避免了传统算法的弊端,实现了LOD实时自适应绘制,并进行了优化.实验结果表明:采用文中技术处理千万级三角面片的模型约1h完成LOD生成,并可在普通计算机上实现实时的自适应绘制.     

虚拟战场环境中地形场景的实时简化技术

三维地形场景实时简化是构建虚拟战场环境中的基本问题,本文论述了一种基于限制四叉树的地形简化算法,实现对规则格网DEM的连续多分辨率表示,结合实时消隐技术,减少场景绘制的三角形数目,提高了大规模DEM地形场景的实时可视化和动态交互的速度。     

Development of a simple model for batch and boundary information updation for a similar ship’s block model

In early 2000,large domestic shipyards introduced shipbuilding 3D computer-aided design (CAD) to the hull production design process to define manufacturing and assembly information.The production design process accounts for most of the man-hours (M/H) of the entire design process and is closely connected to yard production because designs must take into account the production schedule of the shipyard,the current state of the dock needed to mount the ship’s block,and supply information.Therefore,many shipyards are investigating the complete automation of the production design process to reduce the M/H for designers.However,these problems are still currently unresolved,and a clear direction is needed for research on the automatic design base of manufacturing rules,batches reflecting changed building specifications,batch updates of boundary information for hull members,and management of the hull model change history to automate the production design process.In this study,a process was developed to aid production design engineers in designing a new ship’s hull block model from that of a similar ship previously built,based on AVEVA Marine.An automation system that uses the similar ship’s hull block model is proposed to reduce M/H and human errors by the production design engineer.First,scheme files holding important information were constructed in a database to automatically update hull block model modifications.Second,for batch updates,the database’s table,including building specifications and the referential integrity of a relational database were compared.In particular,this study focused on reflecting the frequent modification of building specifications and regeneration of boundary information of the adjacent panel due to changes in a specific panel.Third,the rollback function is proposed in which the database (DB) is used to return to the previously designed panels.     

Adaptive voxels: interactive rendering of massive 3D models

We present a novel approach for interactive rendering of massive 3D models. Our approach integrates adaptive sampling-based simplification, visibility culling, out-of-core data management and level-of-detail. We use a unified scene graph representation for acceleration techniques. In preprocessing, we subdivide large objects, and build a BVH clustering hierarchy. We make use of a novel adaptive sampling method to generate LOD models: AdaptiveVoxels. The AdaptiveVoxels reduces the preprocessing cost and our out-of-core rendering algorithm improves rendering efficiency. We have implemented our algorithm on a desktop PC. We can render massive CAD and isosurface models, consisting of hundreds of millions of triangles interactively with little loss in image quality.     

3DXML文件格式解析及应用

3DXML文件格式是一种重要的轻量化CAD数据格式,通过对3DXML文件格式的分析,论述了一种基于MSXML解析器的文件解析技术。这种解析方式可以快速提取3DXML文件中的重要信息,通过对几何及属性信息的重构,建立整个装配体场景,使用文件中的多分辨率模型,可以提高较大模型的渲染速度。最后给出了基于3DXML文件格式的轻量化CAD浏览器的应用实例。     

A single solution method for converting 2D assembly drawings to 3D part drawings

Although solid models play a central role in modern CAD systems, 2D CAD systems are still commonly used for designing products without complex curved faces. Therefore, an important task is to convert 2D drawings to solid models, and this is usually carried out manually even in present CAD systems. Many methods have been proposed to automatically convert orthographic part drawings of solid objects to solid models. Unfortunately, products are usually drawn as 2D assembly drawings, and therefore, these methods cannot be applied. A further problem is the difficult and time-consuming task of decomposing 2D assembly drawings into 2D part drawings. In previous work, the authors proposed a method to automatically decompose 2D assembly drawings into 3D part drawings, from which 2D part drawings can be easily generated. However, one problem with the proposed method was that the number of solutions could easily explode if the 2D assembly drawings became complex. Building on this work, here we describe a new method to automatically convert 2D assembly drawings to 3D part drawings, generating a unique solution for designers regardless of the complexity of the original 2D assembly drawings. The only requirement for the approach is that the assembly drawings consist of standard parts such as bars and plates. In 2D assembly drawings, the dimensions, part numbers and parts lists are usually drawn, and the proposed method utilizes these to obtain a unique solution.     

Simplifying Character Skins with Analytic Error Metrics

Traditionally, levels of detail (LOD) for animated characters are computed from a single pose. Later techniques refined this approach by considering a set of sample poses and evaluating a more representative error metric. A recent approach to the character animation problem, animation space, (AS) provides a framework for measuring error analytically. The work presented here uses the animation-space framework to derive two new techniques to improve the quality of LOD approximations.
First, we use an animation-space distance metric within a progressive mesh-based LOD scheme, giving results that are reasonable across a range of poses, without requiring that the pose space be sampled.
Second, we simplify individual vertices by reducing the number of bones that influence them, using a constrained least-squares optimization. This influence simplification is combined with the progressive mesh to form a single stream of simplifications. Influence simplification reduces the geometric error by up to an order of magnitude, and allows models to be simplified further than is possible with only a progressive mesh.
Quantitative (geometric error metrics) and qualititative (user perceptual) experiments confirm that these new extensions provide significant improvements in quality over traditional, naïve simplification; and while there is naturally some impact on the speed of the off-line simplification process, it is not prohibitive.     

Wavelet-based multiresolution analysis of irregular surface meshes

We extend Lounsbery's multiresolution analysis wavelet-based theory for triangular 3D meshes, which can only be applied to regularly subdivided meshes and thus involves a remeshing of the existing 3D data. Based on a new irregular subdivision scheme, the proposed algorithm can be applied directly to irregular meshes, which can be very interesting when one wants to keep the connectivity and geometry of the processed mesh completely unchanged. This is very convenient in CAD (computer-assisted design), when the mesh has attributes such as texture and color information, or when the 3D mesh is used for simulations, and where a different connectivity could lead to simulation errors. The algorithm faces an inverse problem for which a solution is proposed. For each level of resolution, the simplification is processed in order to keep the mesh as regular as possible. In addition, a geometric criterion is used to keep the geometry of the approximations as close as possible to the original mesh. Several examples on various reference meshes are shown to prove the efficiency of our proposal.     

有限元领域中多态模型误差分析方法

基于特征造型技术的三维CAD系统目前已广泛应用于产品设计,同时CAE在产品设计与优化中也起到了越来越重要的作用.而有限元是最为广泛使用的CAE方法之一.由CAD系统建立的模型在进行有限元分析之前,通常需要根据分析需要对模型进行简化,如何分析模型简化前后对有限元计算结果的影响程度是CAD模型到CAE模型自动转化的首要步骤.将模型因特征的简化而形成的各种状态的模型称为多态模型.针对确保一定分析精度,节省计算资源的需求,根据有限元误差理论提出了分析不同简化模型对有限元分析结果造成的误差的方法,且通过数据实例得到验证,根据误差分析方法提出模型误差层次的概念,为有限元领域中多态模型的生成提供了新的思路.     

基于层次细节模型的遮挡裁剪算法

遮挡裁剪和应用层次细节模型是两种有效的三维复杂场景渲染加速算法，为了快速地进行三维复杂场景的渲染，提出了一种结合层次细节模型与遮挡裁剪技术的算法框架，该算法首先在预处理阶段，将场景划分成不同空间层次结构；然后在运行时刻，对较高的空间层次，可应用遮挡裁剪技术判别场景的可见性，并裁剪掉不可见场景部分，而在局部的较低层次上，则应用网格简化方法来选择适当的模型层次细节，实验结果显示，该算法取得了较好的加速性能。     

Toward standardized exchange of plant 3D CAD models using ISO 15926

Plant three-dimensional (3D) computer-aided design (CAD) models typically consist of logical configuration, equipment specifications and ports, and 3D shapes. Because 3D CAD models are used as master information throughout a plant’s entire lifecycle and many stakeholders are involved in such lifecycle, providing a method for sharing plant 3D CAD models among various stakeholders is very important. Standard 15926 from the International Organization for Standardization (ISO 15926) is a family of standards that is intended to support the sharing and integrating of all information during the life of a process plant. Therefore it is important for ISO 15926 to support plant 3D CAD models. In order to address this issue, this study investigates a standardized method to exchange plant 3D CAD models using ISO 15926. Information requirements regarding plant 3D CAD models are established, and then ISO 15926 reference data (classes, attributes, and templates) are extended to cover information requirements. For demonstration of the proposed method, we developed a prototype platform where plant 3D CAD models in ISO 15926 are loaded and retrieved.     

Reducing complexity in polygonal meshes with view-based saliency

Salient features in 3D meshes such as small high-curvature details in the middle of largely flat regions are easily ignored by most mesh simplification methods. Nevertheless, these features can be perceived by human observers as perceptually important in CAD models. Recently, mesh saliency has been introduced to identify those visually interesting regions. In this paper, we apply view-based mesh saliency to a purely visual method for surface simplification from two approaches. In the first one, we propose a new simplification error metric that considers polygonal saliency. In the second approach, we use viewpoint saliency as a weighting factor of the quality of a viewpoint in the simplification algorithm. Our results show that saliency can improve the preservation of small but visually significant surfaces even in visual algorithms for surface simplification. However, this comes at a price, because logically some other low-saliency regions in the mesh are simplified further.     

一种基于块和视点相关的大范围地形简化方法与实现

文章简要总结了LOD进行地形简化的一般方法,介绍了一种通过稀疏采样技术实现LOD自动生成的算法。结合DEM均匀网格模型,以“块”作为地表模型大面积简化的空间单位,同时考虑了视点视向相关因素的影响,建立了多LOD数据结构保存各层模型,大大降低了大范围地景的复杂度和计算量,有效地简化了地表模型的绘制,提高了地景生成效率。该方法通过VisualC++6.0和OpenGL编程实现了一个三维的复杂地景生成系统,进一步验证了算法的有效性。     

保持外观的CAD模型轻量化技术

随着CAD/CAM技术的发展,整个产品的设计、虚拟制造和数字化样机都可在计算机中完成,使得包含大量数据的复杂装配体(即大装配体)的设计成为产品设计过程中的必需元素。由于大装配体模型数据量庞大,在普通PC机中处理极为不便,为了提高处理速度,需要对大装配体模型进行简化。在不改变装配模型格式和整体外观的前提下,提出了两种装配体模型的轻量化方案：1)从装配体中删除隐藏的零部件;2)从装配体中删除隐藏的特征。零件和特征的可见性是通过从多个视点预渲染装配模型,然后读取渲染缓冲区的结果并进行分析而得到。实验结果证实该算法能在不改变CAD模型格式和外观的前提下准确地删除装配体中的隐藏零件和特征。