Frederik W. Jansen

Feature modelling and conversion: key concepts to concurrent engineering

Abstract Feature modelling is a relatively new development in CAD/ CAM. Whereas in solid modelling only information about the geometry of products is stored, in feature modelling also functional information is stored in the product model. One aim of this article is to give an overview of the main concepts in feature modelling, another is to indicate the issues in feature modelling that are relevant for further research. There is much confusion about what features actually are, and therefore definitions, classifications and examples of features are first given. Because feature modelling builds on solid modelling, an overview of advanced solid modelling is given, with emphasis on the concepts of parametric and constraint-based modelling. Attention is next focused on representation of features. The two most important ways to define features in a product model, feature recognition from a geometric model and design by features, are then discussed. Design by features is illustrated by the GeoNode system. One of the main themes in this article is that for different applications, different features are required, and that therefore there is a need for automatic conversion between features. Such conversion is of particular importance for the support of concurrent engineering, in which several engineers from different disciplines work simultaneously on the design of a product.

Interaction in virtual world views-linking 3D GIS with VR

To support 3D GIS interaction within VR-environments we propose a multi-view approach based on three types of visualization: plan view, model view and world view. The visualization in these views ranges from a conventional map, through a partly symbolic and simplified 3D representation to a full immersive and photo-realistic 3D display. The views can be used simultaneously or intermittently, and each provides a repertoire of interaction possibilities that are apt but not necessarily limited to that view. We are currently developing a 3D GIS&VR system (Karma VI) based on existing GIS and VR technology that uses the three views to support the design, development and presentation of large infrastructure plans in The Netherlands. Operational use of this system showed that the multi-view approach leads to a more sophisticated understanding of those plans.

Data structures for ray tracing

Methods to improve the efficiency of the ray tracing process are reviewed. Special attention is given to algorithms for tracing a ray through box and cell structures of hierarchical box and spatial subdivision methods.

A multi-view VR interface for 3D GIS

Abstract Virtual reality is becoming a popular tool to visualize 3D GIS data. Direct interaction with the GIS data, however, is often limited. In this paper, we present a multi-view approach to support 3D GIS interaction within VR-environments. The multi-view approach is based on three types of visualization: plan view, model view and world view. The plan view visualizes the data as a conventional cartographic map. The model view provides a 3D birds-eye view on a partly symbolic and simplified 3D representation of the data. The world view gives the full immersive and photo-realistic 3D display. These views or modes can be used simultaneously or intermittently, and each provides a repertoire of interaction possibilities that is apt — but not necessarily limited — to that kind of visualization and interaction. This multi-view approach is implemented in the Karma VI system, using existing GIS and VR technology. We describe the multi-view approach, the system components and the internal data models, and how CAD models can be imported and be made consistent with the GIS data.

Hybrid scheduling for parallel rendering using coherent ray tasks

Parallelising ray tracing with a data parallel approach allows rendering of arbitrarily large models, but the inherent load imbalances may lead to severe inefficiencies. To compensate for the uneven load distribution, demand-driven tasks may be split off and scheduled to processors that are less busy. We propose a hybrid scheduling algorithm which brings tasks and data together according to coherence between rays. The amount of demand-driven versus data parallel tasks is a function of the coherence between rays and the amount of imbalance in the basic data-parallel load. Processing power, communication and memory are three resources which should be evenly used. Our current implementation is assessed against these requirements, showing good scalability and very little communication at the cost of a slightly larger memory overhead.

Accurate overlaying for mobile augmented reality

Mobile augmented reality requires accurate alignment of virtual information with objects visible in the real world. We describe a system for mobile communications to be developed to meet these strict alignment criteria using a combination of computer vision, inertial tracking and low-latency rendering techniques. A prototype low-power and low-latency renderer using an off-the-shelf 3D card is discussed.

Multi-view Feature Modelling for Design and Assembly

Abstract Different applications require the use of different feature sets, and hence multiple views and multiple feature models will have to be supported. One such application is assembly planning, for which a short description and two feature classes are given. Further an interactive design-by-feature approach is presented and illustrated with the GeoNode system. To support multi-view feature modeling, a combination of a design-by-features approach and feature conversion is proposed, where the system maintains the consistency between the different feature models.

Two methods for improving the efficiency of ray casting in solid modelling

In solid modelling based on constructive solid geometry and primitive instancing, ray casting is a very suitable technique for visualization of models on a raster display. In its present form, it is, however, too inefficient for interactive use. Two methods for improving the efficiency are given here. The first uses scan-line interval enclosures instead of box enclosures, and also bypasses non-contributing nodes during each traversal of the CSG (constructive solid geometry) tree. The second refines the image step by step by subdivision, thereby avoiding explicit computation of the intensities of many pixels of the image. The second method reduces computing time more than the first, but has the disadvantage that slivers may occasionally be lost from the image.

Source Selection for the Direct Lighting Computation in Global Illumination

Computation of the global illumination in a scene can be improved by separating the direct component of the lighting, which is received by a patch directly from light sources, from the indirect component, which is received by intermediate interreflection from other patches. The indirect component is calculated during the preprocessing and is stored as the radiosity shading at the patch. The direct component is calculated during the rendering phase by tracing shadow rays like in conventional ray tracing. The number of shadow rays can be reduced by exploiting shadow coherence, and by making a selection for the number of light sources that are taken into account for the direct lighting computation. Different criteria to select these sources are given.

Comparing simplification and image-based techniques for 3D client-server rendering systems

A mathematical model is presented for comparing geometric and image-based simplification methods. Geometric simplification reduces the number of polygons in the virtual object and image-based simplification replaces the object with an image. Our model integrates and extrapolates existing accuracy estimates, enabling the comparison of different simplification methods in order to choose the most efficient method in a given situation. The model compares data transfer and rendering load of the methods. Byte size and expected lifetime of simplifications are calculated as a function of the desired visual quality and the position and movement of the viewer. An example result is that, in typical viewing and rendering conditions and for objects with a radius in the order of one meter, imposter techniques can be used at viewing distances above 15 meters. Below that, simplified polygon objects are required and, below one meter distance, the full-resolution virtual object has to be rendered. An electronic version of the model is available on the web.