Wenyu Chen

Kernel modeling for molecular surfaces using a uniform solution

In this paper, a rational Bezier surface is proposed as a uniform approach to modeling all three types of molecular surfaces (MS): the van der Waals surface (vdWS), solvent accessible surface (SAS) and solvent excluded surface (SES). Each molecular surface can be divided into molecular patches, which can be defined by their boundary arcs. The solution consists of three steps: topology modeling, boundary modeling and surface modeling. Firstly, using a weighted @a-shape, topology modeling creates two networks to describe the neighboring relationship of the molecular atoms. Secondly, boundary modeling derives all boundary arcs from the networks. Thirdly, surface modeling constructs all three types of molecular surfaces patch-by-patch, based on the networks and the boundary arcs. For an SES, the singularity is specially treated to avoid self-intersections. Instead of approximation, this proposed solution can produce precise shapes of molecular surfaces. Since rational Bezier representation is much simpler than a trimmed non-uniform rational B-spline surface (NURBS), computational load can be significantly saved when dealing with molecular surfaces. It is also possible to utilize the hardware acceleration for tessellation and rendering of a rational Bezier surface. CAGD kernel modelers typically use NURBSs as a uniform representation to handle different types of free-form surface. This research indicates that rational Bezier representation, more specifically, a bi-cubic or 2x4 rational Bezier surface, is sufficient for kernel modeling of molecular surfaces and related applications.

Generalized hierarchical NURBS for interactive shape modification

In a three dimensional (3D) environment, having the capability of local shape refinement and modification is highly desired for interactive free-form shape design. The introduction of hierarchical B-spline has provided a nice mechanism to control the influence of refinement to the locality for tensor-product B-spline surfaces. This paper extends the idea of hierarchical B-splines to non-uniform rational B-spline (NURBS) surface and a generalized hierarchical NURBS (H-NURBS) is proposed. Based on the modification of control points or weights of the H-NURBS surface, we can paste a NURBS surface onto an existing H-NURBS surface. Two approaches with different mechanisms are proposed: the base plus detail mechanism and the replacement mechanism. Different kinds of interactive devices like mouse, stylus and glove can be used to manipulate the H-NURBS.

Surface skinning using periodic T -spline in semi-NURBS form

NURBS skinning is a powerful and effective process in Computer Aided Geometric Design (CAGD). It constructs a surface by interpolating a set of cross sectional NURBS curves. These curves however may not be compatible, i.e., they have different knot vectors. This incompatibility is conventionally solved by knot refinement bringing all curves to share the same knot vector, which leads to an explosion in the number of control points defining the skinned surface. Another disadvantage of NURBS skinning is the difficulty of local modification: adjusting one cross section may result in a global change of the surface. In this paper, periodic T -spline in semi-NURBS form is discussed. Surface skinning using such T -splines is able to handle closed cross sections, to support local modifications and to control smoothness along the cross sectional curves. We provide explicit formulae for constructing such T -spline skinned surfaces, which avoid solving a large system of equations. Experimental results and theoretical analysis confirm that our approach is better than NURBS skinning as it generates surfaces with fewer control points.

Real-time 3D markerless multiple hand detection and tracking for human computer interaction applications

In this paper we present a purely vision based implementation of markerless hand detection and tracking system which effectively detects and tracks the hand positions irrespective of hand orientation. A shape based detection algorithm using a new line approximation technique followed by an adaptive minimum distance classifier based tracking technique is implemented. The technique is very generic and can be practically used in all types of immersive and semi-immersive environments like simulations, three-dimensional (3D) games, visually assisted medical surgery and other human-computer interactive applications.n The proposed technique overcomes certain limitations of glove based, handheld object based and marker based techniques for a truly immersive experience. The technique also overcomes the main limitation of previous vision based hand tracking systems by providing much larger degrees of freedom essential for effective virtual reality systems. The novelty of the technique proposed is that it separates the detection and tracking parts and therefore allows tracking of multiple hands in a 3D space for real-time interaction.

Freeform-based form feature modeling using a hierarchical & multi-resolution NURBS method

In a three dimensional (3D) environment, non-uniform rational B-spline surfaces (NURBS) have been a standard in CAD industry for free-form shape modelling. Feature based design is widely used in CAD design. This paper addresses the issue of form feature design on free-form surfaces. Based on the multi-resolution and refinement scheme, the Hierarchical NURBS (H-NURBS) representation is proposed for localized form feature modelling. More specifically, the patch-based form feature modelling concept will be discussed. H-NURBS representation introduced here not only offers powerful functionality for form feature modeling on freeform surface, but also overcomes the problems inherited from the traditional control point based shape modelling. We will investigate first the extrusion operation to create various form features on freeform surfaces. Patterning operation of form features as well as form feature cut-&-paste operation on freeform surfaces/shapes will be studied for efficient and effective local shape design. Interactive methodology and techniques will be developed for the patch-based form feature modelling with an emphasis on the native and easy parameter control.

2D motion detection bounded hand 3D trajectory tracking and gesture recognition under complex background

In this paper, a 2D motion detection bounded hand 3D trajectory tracking and gesture recognition system is proposed for virtual reality interactions. First, the Bayes decision rule for classification of background and foreground is utilized to automatically locate the hand that bounded within a rectangle, and then the trajectory of the hand in 3D space is tracked by mean shift particle filter and stereo imaging. The skin color feature is exploited for image matting that effectively segment the hand contour in video sequence automatically. Finally the hand gesture is recognized by the connected component analysis and line approximation.n The proposed technique works without any markers or constraints, overcomes the disturbance of arms and faces in the scene, and can recognize multiple hands with different gestures under complex background.

T-splines in VRML

T-splines are increasingly popular in design and animation. However, since it is not supported by VRML/X3D, T-spline visualization is not available for the use online. This paper proposes the T-spline VRML node, which allows the end users to utilize T-splines for complex model design and online visualization with relatively small number of control points. Similar with the NURBS based and polygon based VRML nodes, T-spline VRML node can support geometry, color, texture, LOD and animation. The file size required for T-spline VRML node to represent a same complex model can be substantially minimized compared with the ones with NURBS based and polygonal based VRML nodes. Thus, it is feasible for data transmission on internet. A new data structure is proposed to represent T-spline surfaces in VRML for easy editing. The implementation details and the application examples of the proposed node are discussed.

Triangular Bézier sub-surfaces on a triangular Bézier surface

This paper considers the problem of computing the Bezier representation for a triangular sub-patch on a triangular Bezier surface. The triangular sub-patch is defined as a composition of the triangular surface and a domain surface that is also a triangular Bezier patch. Based on de Casteljau recursions and shifting operators, previous methods express the control points of the triangular sub-patch as linear combinations of the construction points that are constructed from the control points of the triangular Bezier surface. The construction points contain too many redundancies. This paper derives a simple explicit formula that computes the composite triangular sub-patch in terms of the blossoming points that correspond to distinct construction points and then an ecient algorithm is presented to calcula te the control points of the sub-patch.

Monge mapping using hierarchical NURBS

Texture mapping is an efficient and effective tool in computer graphics and animation. While computationally very cost-effective, texture mapping may produce non-realistic appearances of shapes in 3D environment, especially when viewing closely. To improve the realism of 3D modeling, bump mapping technique is developed to add details with the 3D models on top of texture mapping. Bump mapping, however, offers only simple and visual enhancement. Displacement mapping technique can further improve the localized detail of geometry. In this paper, Monge mapping technique is developed for detail and local shape modification of NURBS represented geometry in a 3D environment. Based on multiresolution and refinement schemes, Hierarchical NURBS (H-NURBS) is first investigated to design a mechanism for the purpose of carrying localized geometric information. Monge mapping on H-NURBS patch can be easily performed via simple cut-and-paste operation. Parametric control of the local shapes is developed to facilitate easier and better 3D local modeling.

An architecture of a VR simulation system for cardiac intervention

Cardiovascular diseases account for a major cause of deaths in many developed countries. To treat cardiovascular diseases, cardiac minimally intervention is widely used as an effective yet complicated solution. Training of cardiac intervention is thus playing a crucial role. This paper addresses the use of Virtual Reality (VR) technology for the simulated training of cardiac intervention. In particular, the paper describes the architecture of a VR simulation system for cardiac intervention focusing on VR hardware, software and methodology is used in As an enabling technology, Graphics Processing Unit (GPU) is applied in this work to enhance cardiac modeling, cardiac visualization, and cardiac interactive simulation with the VR simulation environment.