CAD Objects Research Articles

Automated Material Selection and Environmental Assessment in the Context of 3D Building Modelling

There is significant scope for increasing the performance of commercial buildings across all dimensions of sustainability. For this to be realised, however, requires the development of more advanced real time assessment systems which provide automated eco-efficiency performance checking direct from 3D CAD as a regular and integral part of the design process rather than in late or post-design where options are more restricted. An integrated approach to directly link choice of materials and their environmental impacts with 3D CAD model object-oriented files containing significant building information, has been developed by the Cooperative Research Centre for Construction Innovation as a first step in this process. From 3D CAD objects, the system called LCADesign* automatically obtains the quantities of all building components associated with the selected products, calculates a complete inventory of constituents of building products, and links these to a Life Cycle Inventory database of building materials. The Life Cycle Inventory database includes all resource usage and emissions to the environment from the extraction of raw material resources, through their manufacture, transport, use, recycling, and maintenance. A number of performance assessment indicators can then be used to compare options in the choice of materials or design. An application to a commercial building project in Melbourne, Australia is provided to illustrate the potential of virtual building modelling.

Modeling Heterogeneous Objects in CAD

AbstractA heterogeneous object (HO) modeling system independent of any commercial CAD software packages is introduced in this paper. Through this system, CAD models can be converted into 2D slices with heterogeneous material information for the fabrication of rapid prototyping technique. In this framework, volumetric dataset (VD) is employed to represent the material variations, which offers flexible manipulability to HO representation, while geometry model is used to describe the shape of an object, which can guarantee the accuracy of final HO slices. Two schemes are used to evaluate the composition variations in this system. Ray casting is utilized to render the HO volumetric dataset with the property of transparency.

Development changes of geometric layout product, developed by means of computer aided design

Contains results of development of modification formation methodology in a product geometrical mockup made by means of CAD system. Change process of a CAD data (assembly structures, details) and influencing on a product structure is considered. The analysis of the assembly version creations algorithm, which creates a product structure with certain serial number, is carried out. The algorithms of CAD user environment creations, restriction of CAD object and CAD object cancellation algorithm are created.

Local feature extraction and matching partial objects

A primary shortcoming of existing techniques for hree-dimensional (3D) model matching is the reliance on global information of the model’s structure. Models are matched in their entirety, depending on overall topology and geometry information. A currently open challenge is how to perform partial matching. Partial matching is important for finding similarities across part models with different global shape properties and for the segmentation and matching of data acquired from 3D scanners. This paper presents a Scale–Space feature extraction technique based on recursive decomposition of polyhedral surfaces into surface patches. The experimental results presented in this paper suggest that this technique can potentially be used to perform matching based on local model structure. In our previous work, Scale–Space decomposition has been used successfully to extract features from mechanical artifacts. Scale–Space techniques can be parameterized to generate decompositions that correspond to manufacturing, assembly or surface features relevant to mechanical design. One application of these technique is to support matching and content-based retrieval of solid models. This paper shows how a Scale–Space technique can extract features that are invariant with respect to the global structure of the model as well as small perturbations that 3D laser scanning process introduce. In order to accomplish this, we introduce a new distance function defined on triangles instead of points. We believe this technique offers a new way to control the feature decomposition process, which results in the extraction of features that are more meaningful from an engineering viewpoint. The new technique is computationally practical for use in indexing large models. Examples are provided that demonstrate effective feature extraction on 3D laser scanned models. In addition, a simple sub-graph isomorphism algorithm was used to show that the feature adjacency graphs, obtained through feature extraction, are meaningful descriptors of 3D CAD objects. All of the data used in the experiments for this work is freely available at: http://www.designrepository.org/datasets/.

Dynamic CAD objects for structural optimization in preliminary aircraft design

Two new concepts for supporting CAD of repetitively stiffened structures are presented. The two concepts are called D-operator and K-operator, respectively. They have been developed to support preliminary aircraft design and are therefore illustrated by using typical aircraft structures. However, the methods could be applied to any repetitive CAD structure. Cooperation with the software supplier made it possible to implement the K-operator professionally. Sample structures generated with this concept will be illustrated and the results of a CAD based optimization using dynamic objects will be discussed. An outlook will give some ideas for further development and improvements of the method.

Augmented tangible interfaces for product assembly planning

Collaborative work has became an increasingly crucial aspect of engineering design as teams grow larger and more diverse. However, the complexity of the CAD system's interface can introduce a participation barrier. In a design review context, this barrier prevents the diverse team members from directly interacting with the CAD objects. The goal of the research presented in this paper is to consider an alternative to two-dimensional desktop-based interfaces for a design review. Using an augmented reality technology, we present a set of tangible user interfaces that allows the users to see virtual three-dimensional models and to manipulate them naturally as if they were real, physical objects.

Structure Recovery via Hybrid Variational Surface Approximation

Aiming at robust surface structure recovery, we extend the powerful optimization technique of variational shape approximation by allowing for several different primitives to represent the geometric proxy of a surface region. While the original paper only considered planes, we also include spheres, cylinders, and more complex rollingball blend patches. The motivation for this choice is the fact that most technical CAD objects consist of patches from these four categories. The robust segmentation and global optimization properties which have been observed for the variational shape approximation carry over to our hybrid extension. Hence, we can use our algorithm to segment a given mesh model into characteristic patches and provide a corresponding geometric proxy for each patch. The expected result that we recover surface structures more robustly and thus obtain better approximations with a smaller number of primitives, is validated and demonstrated on a number of examples.

A new subdivision based approach for piecewise smooth approximation of 3D polygonal curves

This paper presents an algorithm dealing with the data reduction and the approximation of 3D polygonal curves. Our method is able to approximate efficiently a set of straight 3D segments or points with a piecewise smooth subdivision curve, in a near optimal way in terms of control point number. Our algorithm is a generalization for subdivision rules, including sharp vertex processing, of the Active B-Spline Curve developed by Pottmann et al. We have also developed a theoretically demonstrated approach, analysing curvature properties of B-Splines, which computes a near optimal evaluation of the initial number and positions of control points. Moreover, our original Active Footpoint Parameterization method prevents wrong matching problems occurring particularly for self-intersecting curves. Thus, the stability of the algorithm is highly increased. Our method was tested on different sets of curves and gives satisfying results regarding to approximation error, convergence speed and compression rate. This method is in line with a larger 3D CAD object compression scheme by piecewise subdivision surface approximation. The objective is to fit a subdivision surface on a target patch by first fitting its boundary with a subdivision curve whose control polygon will represent the boundary of the surface control polyhedron.

A new CAD mesh segmentation method, based on curvature tensor analysis

This paper presents a new and efficient algorithm for the decomposition of 3D arbitrary triangle meshes and particularly optimized triangulated CAD meshes. The algorithm is based on the curvature tensor field analysis and presents two distinct complementary steps: a region based segmentation, which is an improvement of that presented by Lavoue et al. [Lavoue G, Dupont F, Baskurt A. Constant curvature region decomposition of 3D-meshes by a mixed approach vertex-triangle, J WSCG 2004;12(2):245–52] and which decomposes the object into near constant curvature patches, and a boundary rectification based on curvature tensor directions, which corrects boundaries by suppressing their artefacts or discontinuities. Experiments conducted on various models including both CAD and natural objects, show satisfactory results. Resulting segmented patches, by virtue of their properties (homogeneous curvature, clean boundaries) are particularly adapted to computer graphics tasks like parametric or subdivision surface fitting in an adaptive compression objective.

A topology-based filling algorithm

In this paper we present a fast-recursive fully automated topology-based algorithm for filling in the interiors of objects that appear in a binary image. The algorithm is based on two topological properties of the image contours: perimeter coincidence and interiority. Based on these parameters the algorithm performs a tree-structured region classification. The final filling is done according to the labels of the tree leaves. The algorithm is well suited to cases in which contours overlap and ambiguities may arise about which regions to fill. The algorithm has been tested with three-dimensional solid objects given by surface representations, both for simple man-made CAD objects and for complicated images taken from human computer tomographies. A table shows the execution times taken by the algorithm for several medical volume data sets.

X-ray modeling for industrial applications

A computer package for the simulation of the X-ray imaging process in nondestructive evaluation (NDE) is presented. The components of the radiographic inspection system are considered independently, i.e. the characteristics of the source, the geometry and the material properties of objects and defects, as well as the imaging process itself. The model is based on a ray tracer technique describing the attenuation of the radiation. The scattering effect is included in terms of built-up factors. A CAD-interface provides the opportunity to arrange independent CAD objects, e.g. the component geometry or defect shapes, defining a testing scheme. Complicated defect shapes are created by a preprocessor, the built-up factors can be received from experiments or from a separate model using an efficient solution of the scattering problem based on the theory of Markovian processes with random structure.

Virtual assembly planning

The technique of virtual reality facilitates three-dimensional interactions with objects, as for example changes of positions and orientations of objects as well as connection of parts. This forms the ideal basis for spatial assembly planning of products. Fraunhofer-Institute for Industrial Engineering (IAO) has been developing a planning system that uses this feature to carry out assembly planning operations. The virtual assembly planning system makes it possible to interactively assemble and disassemble components and modules in a virtual surrounding. The first prototype of the system received the “BYTE – Best of Systems” award at the Systems 96 Computer Fair in Munich. It applies VirtualANTHROPOS—a virtual model of a person—for executing assembly operations. It is connected by interface to a CAD system and can present CAD objects in a virtual production environment. Based on the user interactions with the virtual objects, a precedence graph is generated and the time of assembly and cost is determined. This article reports on the advantages of Concurrent Engineering and the development of right first time methods such as virtual assembly planning and virtual ergonomic prototyping. © 2000 John Wiley & Sons, Inc.

Modelbase Partitioning Using Property Matrix Spectra

In this paper, we present aneigenvalueorspectral-basedrepresentation for CAD models to be used in conjunction with the more traditional attributed graph based representation of these models. The eigenvalues provide a gross description of the structure of the objects and help to divide a large modelbase into structurally homogeneous partitions. Models in each partition are next hierarchically organized according to the algorithm we presented in a previous paper [IEEE Trans. Pattern Anal. Machine Intell.17, 1995, 321--332]. In recognition, gross features computed from an object in a range image are used to prune the modelbase by selecting a few “favorable” partitions in which the correct object model is likely to lie. We also model the perturbations in the eigenvalues computed from objects in real scenes and show how this perturbation model can be used effectively during recognition. The partitioning experiments presented here are for real range images using a modelbase of 125 CAD objects with planar, cylindrical, and spherical surfaces. From our recognition results, we observe that for a reasonable degree of error in the low-level processes (surface segmentation and grouping), the correct partition is always included. Experimental results also point to a significant increase in recognition speed, even on modelbases much smaller than the ones we consider here.

Using geometric hashing to repair CAD objects

Problems in CAD software sometimes cause defects in the boundaries of polyhedral objects-small gaps bounded by edges incident to one polyhedron face. Using geometric hashing, algorithms can resolve this problem, which has vexed layered manufacturing. Similar techniques hold promise for solving problems in such areas as computer vision, medical imaging, and molecular biology.

A Study of Work Flow Model and Its Application to Concurrent Engineering

Since CAD objects are frequently changed or added to in concurrent engineering, the following items are necessary

Visualization of 3‐D computer‐aided design objects

There are many significant human factors issues associated with the design and visualization of complex, computer‐generated images. One such issue is to determine the most effective techniques for providing engineers with realistic three‐dimensional (3‐D) objects. Differences in subjects’ ability to discriminate between the shape of two 3‐D, perspective, computer‐aided design‐type (CAD‐type) objects were investigated for various levels of monocular coding techniques and the binocular cue stereopsis. Performance was assessed at all combinations of five levels of monocular cues and two levels of disparity. The task was similar to the classic mental rotation paradigm except that subjects were provided with the ability to rotate one of the objects using a two‐dimensional (2‐D) joystick. Results indicate that interposition was the only depth cue that significantly enhanced subject performance. One explanation for the lack of significance of stereopsis is that, for this particular task, depth information provided by disparity was not needed. Detailed analysis of object rotation data using an orientation index (OI) suggests that subjects employed a feature‐by‐feature comparison task strategy. With tools that can evaluate cognitive activity such as the mental rotation paradigm and orientation index, researchers can learn more about how designers visualize and understand 3‐D CAD objects.

Finite element mesh generation of arbitrary solid objects in cad

This paper discusses a three-dimensional solid modelling scheme developed with B-spline as a basis and the techniques for transforming the solid model geometric data into formal solid finite elements. A solid is represented by the scheme as a union of quasi-disjointed cells which are bounded by orthogonal B-spline curves. An algorithm developed converts the cells into solid finite elements. The modelling technique is a powerful tool in the CAD/CAM environment because it is particularly useful for the design and analysis of curved solid mechanical parts.

Image processing of real-time X-ray images of honeycomb core sandwich panels : Crostack, H.-A.; Reimers, W.; Schroeder, P. Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23–28 Apr. 1989, Vol. 2, pp. 1215–1217. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989

A computer package for the simulation of the X-ray imaging process in nondestructive evaluation (NDE) is presented. The components of the radiographic inspection system are considered independently, i.e. the characteristics of the source, the geometry and the material properties of objects and defects, as well as the imaging process itself. The model is based on a ray tracer technique describing the attenuation of the radiation. The scattering effect is included in terms of built-up factors. A CAD-interface provides the opportunity to arrange independent CAD objects, e.g. the component geometry or defect shapes, defining a testing scheme. Complicated defect shapes are created by a preprocessor, the built-up factors can be received from experiments or from a separate model using an efficient solution of the scattering problem based on the theory of Markovian processes with random structure.

Expert database concepts for engineering design

The specific semantics of CAD objects are analysed concerning their nature their dynamicity and their consistency during the design process. The nature of CAD objects is concerned with their structure and relationships. The dynamicity is concerned with the evolving nature of the objects, i.e. their behavior. The consistency is concerned with their completeness and relationships with integrity constraints.A new methodology for semantic constraints management and control is defined. It relies extensively on database and expert system technologies for the implementation of new concepts, e.g. logical prototypes of objects and object equivalence class.It provides a sound and unified basis for modelling the dynamic nature of complex objects, concerning both the management of their structure and the certification of the update operations, i.e. the control of their correctness.The functionalities of CADB, a prototype expert database system that supports these features, are detailed. CADB is currently implemented in Prolog on VAX™ 11/785 and APOLLO™ workstations.

Modeling concepts for VLSI CAD objects

VLSI CAD applications deal with design objects that have an interface description and an implementation description. Versions of design objects have a common interface but differ in their implementations. A molecular object is a modeling construct which enables a database entity to be represented by two sets of heterogeneous records, one set describes the object's interface and the other describes its implementation. Thus a reasonable starting point for modeling design objects is to begin with the concept of molecular objects. In this paper, we identify modeling concepts that are fundamental to capturing the semantics of VLSI CAD design objects and versions in terms of molecular objects. A provisional set of user operations on design objects, consistent with these modeling concepts, is also defined. The modeling framework that we present has been found useful for investigating physical storage techniques and change notification problems in version control.