Elsevier

Computer-Aided Design

Volume 33, Issue 5, 1 April 2001, Pages 403-420
Computer-Aided Design

A novel haptics-based interface and sculpting system for physics-based geometric design

https://doi.org/10.1016/S0010-4485(00)00131-7Get rights and content

Abstract

Conventional geometric design techniques based on B-splines and NURBS often require tedious control-point manipulation and/or painstaking constraint specification via unnatural mouse-based computer interfaces. In this paper, we propose a novel and natural haptic interface and present a physics-based geometric modeling approach that facilitates interactive sculpting of spline-based virtual material. Using the PHANToM haptic device, modelers can feel the physically realistic presence of virtual spline objects and interactively deform virtual materials with force feedback throughout the design process. We develop various haptic sculpting tools to expedite the deformation of B-spline surfaces with haptic feedback and constraints. The most significant contribution of this paper is that point, normal, and curvature constraints can be specified interactively and modified naturally using forces. To achieve the real-time sculpting performance, we devise a novel dual representation for B-spline surfaces in both physical and mathematical space: the physics-based mass-spring model is mathematically constrained by the B-spline surface throughout the sculpting session. We envision that the integration of haptics with traditional computer-aided design makes it possible to realize all the potential offered by both haptic sculpting and physics-based modeling in CAD/CAM, virtual prototyping, human–computer interface, and medical training and simulation.

Introduction

During the past several decades, standard free-form splines such as B-splines and NURBS are frequently utilized to satisfy various design and manufacturing needs within CAD/CAM systems. They have been employed for the rapid modeling, efficient design and manufacturing of aircraft, ship hulls, automobile bodies, various industrial parts, consumer products, and natural objects. Moreover, free-form splines are of paramount significance to a much wider range of fields such as real-time interactive graphics, scientific visualization, medical imaging, and virtual environments.

Although the theoretical foundations and mathematical properties of free-form splines have been extensively researched, better and more efficient modeling techniques using these splines have evolved rather slowly. Traditional free-form spline modeling is often associated with the tedious and indirect manipulation via a large number of (often irregular) control vertices. In spite of the advent of modern 3D graphics interaction tools, these indirect geometric techniques remain inherently laborious. In contrast, physics-based modeling offers a superior approach to free-form geometric design such that it augments (rather than supercedes) matured geometric modeling techniques, offering users extra advantages. Within the physics-based frame-work, free-form spline models are equipped with mass distributions, internal deformation energies, and other material properties. The models, governed by physical laws, respond dynamically to applied forces in an intuitive and natural manner (see [19], [20] for the details of the physics-based modeling methodology). Refer to Fig. 1 for an example of a variety of shapes each modeled in a matter of seconds by a non-artist.

Despite recent research advances in physics-based modeling, it is not yet possible to achieve the full modeling potential associated with the physics-based design framework. This is due to the fact that existing modeling systems often rely upon 2D mouse-based interfaces for 3D interaction. Direct physical operations on virtual objects with a mouse are not as natural and intuitive as interaction using a 3D interface. To ameliorate, we present a novel haptic approach for the intuitive and natural design of free-form spline models and integrate this easy-to-use interface with physics-based design algorithms (Fig. 2).

Haptics provides users a hand-based mechanism for intuitive, manual interactions with virtual environments towards realistic tactile exploration and manipulation. Haptics-based human–computer interaction has emerged as a critical metaphor in the fields of medicine, education, industry, entertainment, and computer arts. This is primarily because using force-feedback controls, designers, artists, as well as non-expert users can feel the model representation and modify the object directly, thus enhancing the understanding of object properties and the overall design. To date, practical devices for tactile interaction are commercially viable. A typical haptic device provides between two and six degrees of freedom (DOF) and its appearance ranges from a simple joystick to a complex robotic arm. We currently use the six DOF input and three DOF output PHANToM haptic device manufactured by SensAble Technologies. This device includes a pen-like stylus with a click-able button for interaction.

Throughout a large variety of interactive graphics methods, few computer-based modeling techniques have come close to enabling modelers to design various shapes directly with their hands. Our goal is to allow users to reach toward an object, feel the physical presence of its shape, grab the object, manipulate it (with or without deformation), and release it in the desired location. Using a standard haptic device, our hand-based approach permits users to interactively sculpt virtual materials having realistic properties and feel the physically realistic presence with force feedback throughout the design process.

One potential advantage of this research is the integration of haptics with the computer-integrated design and manufacturing cycle. Using haptics in a virtual design environment, designers are able to feel and deform real objects in a natural 3D setting, rather than being restricted to mere 2D projections for input and output. Force feedback provides additional sensory cues to designers. This tactile exploration can afford designers to gain a richer understanding of the 3D nature using the human hand for spatial and temporal interaction. The use of haptics in a virtual design environment promises to increase the bandwidth of information between designers and the synthetic modeling world. Furthermore, the use of haptics in design, analysis, and manufacturing processes can potentially shorten the product development cycle, enhancing the effectiveness of the design and analysis process for industry.

Prior research primarily focused on haptic rendering (i.e. the feeling of rigid surfaces/solids). In contrast, our haptic modeling system allows modelers to interactively deform a non-rigid free-form surface (e.g. a B-spline object) in real-time. The B-spline surface sculpted by our haptic device is a dynamic physics-based model, which inherits all the intrinsic behaviors of physical, real-world objects. The dynamic behaviors of our free-form surfaces result from a set of differential equations and produce intuitive shape variations. From an optimization point of view, our haptic sculpting dynamically optimizes an array of geometric and physical constraints enforced upon an arbitrary set of geometric degrees of freedom (i.e. control vertices). The B-spline surface currently available in our haptic design system is a specific case of a more general D-NURBS [20] object with fixed weights. Our on-going research endeavor is to further extend the haptic system to sculpt more powerful D-NURBS objects.

We develop several high-level haptic sculpting tools to expedite the intuitive modification of spline objects in a natural way. The tools developed in this system allow direct interactive modification of position, tangent, normal, and curvature constraints via forces. One key advantage for introducing these high-level tools into haptic design is that non-expert users are able to concentrate on visual shape variation without necessarily comprehending the underlying (rather complicated) mathematics of object representation. In particular, the B-spline control points and their associated basis functions become transparent to modelers in our haptic design environment, only the objects of interest remain visible from the users’ point of view.

We develop a dual representation for physics-based geometric design. In physical space, a physics-based B-spline surface is discretized into a mass-spring model equipped with material and elastic properties to provide dynamic realism. The physical model provides an efficient, intuitive approach to specify curvature, normal, tangent, and other constraints. This mass-spring model is constrained in mathematical space by the B-spline surface throughout the sculpting session. Its behavior evolves in response to the Lagrangian equations of motion subject to various geometric constraints. The equations of motion are solved in real-time using a tractable numerical solver. Note that the polyhedral representation can be approximated to any user-specified error tolerance making it useful for simultaneous graphics rendering and haptic rendering.

It may be noted that the integration of a haptic interface and physics-based modeling should be of interest to broader communities. This novel approach also presents other value-added potential:

  • The haptics-based system is more user-friendly, more intuitive, and easier-to-use from the viewpoint of both professional designers and non-expert users such as artists; it should appeal to the general public.

  • The haptic interface should be more attractive to computer professionals from diverse application domains. For example, collaborative design, involving a group of artists, computer programmers, and engineering designers, can be readily accomplished.

The remainder of the paper is organized as follows. Section 2 reviews research concerning physics-based modeling. Section 3 presents the mathematical formulations. Section 4 describes the current state of haptics and addresses technical challenges relevant to our haptic sculpting system. Section 5 describes the detailed components of our sculpting system and implementation issues. Section 6 presents the components of the application and addresses the issue of system assessment. Section 7 concludes the paper and outlines future research directions.

Section snippets

Physics-based modeling

Various techniques have been developed to generate fair surfaces that satisfy multiple constraints and optimize an energy-based objective functional [3], [15], [33]. It is also possible to construct dynamic surfaces with natural behavior governed by physical laws [17], [30]. The benefit of physics-based behavior during interactive design is that the development of the surface follows intuitive physical paths and the surfaces react to external manipulation in a predictable way. For example,

Dynamics formulation

We represent a continuous B-spline surface s(u,v) as the combination of a set of basis functions Bi,k and Bj,l with (n+1)×(m+1) control points p(t), where t denotes times(u,v)=i=0nj=0mpi,jBi,k(u)Bj,l(v)

Note that, Bi,k and Bj,l are piecewise polynomials of order k and l, respectively. Both u and v are parametric variables. Their parametric domain is determined by two sets of non-decreasing knot sequences, respectively. In the interest of the space here, we refer readers to Ref. [20] for the

Haptics techniques

Haptics and its associated techniques have been well researched in recent years. A good review of haptics literature can be found in Ref. [23], where the terminology and fundamentals of haptics simulation, including cognitive studies and mechanical requirements, are also detailed. Minsky et al. [14] investigated the conditions required to sustain the illusion of reality in a haptic system. Thompson et al. [32] investigated haptic rendering of NURBS surfaces. The difficulty in rendering NURBS

Sculpting system and implementation

The sculpting system allows the user to reach out toward the surface and click the stylus button to grab hold of the surface. In response, the surface reacts in a physically plausible manner and deforms according to the manipulation of the user. At any time, the user can lock-in changes and set a persistent constraint.

Our haptic system executes in a tight loop for direct manipulation. It constantly evolves the dynamic surface (governed by physical equations) in response to the user's sculpting

Results

This section presents the graphic interface functionalities, details our experimental results, and discusses the system limitation.

Conclusion

We have presented a novel haptics-based interface and sculpting system that facilitates the direct manipulation of dynamic surfaces based on a B-spline formulation. The 3D haptics-based interface is more intuitive and natural than conventional 2D mouse-based interfaces. We have demonstrated a desktop haptic modeling system which is suitable for a spectrum of users ranging from highly trained engineering designers, computer professionals, artists, to even computer illiterates. Our system offers

Acknowledgements

This work was partially supported by NSF grant MIP9527694, NSF CAREER award CCR9896123, NSF grant DMI9896170, ONR grant N000149710402, Intel Corp, and Ford Motor Corp. The authors wish to thank Justine Dachille, Kevin McDonnell, John Woodwark, and several anonymous reviewers for their helpful comments.

Frank Dachille received a BS in Naval Architecture and Marine Engineering from Webb Institute of Naval Architecture in 1994 on a full-tuition scholarship. He worked for two years developing collaborative virtual reality environments at Concurrent Technologies Corporation. He is currently a PhD candidate in Computer Science at the State University of New York at Stony Brook, where he is a research assistant in the Center for Visual Computing (CVC) headed by Dr Arie Kaufman. His current research

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    Frank Dachille received a BS in Naval Architecture and Marine Engineering from Webb Institute of Naval Architecture in 1994 on a full-tuition scholarship. He worked for two years developing collaborative virtual reality environments at Concurrent Technologies Corporation. He is currently a PhD candidate in Computer Science at the State University of New York at Stony Brook, where he is a research assistant in the Center for Visual Computing (CVC) headed by Dr Arie Kaufman. His current research interests include global illumination, volume visualization, volume rendering architectures, physics-based modeling, and virtual reality. For more information, see http://www.cs.sunysb.edu/~dachille.

    Hong Qin is an Assistant Professor of Computer Science at State University of New York at Stony Brook, where he is also a member of the Center for Visual Computing (CVC). He received his BS (1986) degree and his MS degree (1989) in Computer Science from Peking University in Beijing, People's Republic of China. He received his PhD (1995) degree in Computer Science from the University of Toronto. During 1989–1990, he was research scientist at North-China Institute of Computing Technologies. During 1990–1991, he was a PhD candidate in Computer Science at the University of North Carolina at Chapel Hill. During 1996–1997, he was an Assistant Professor of Computer and Information Science and Engineering at the University of Florida. He received the Honor Student Award from 1983 to 1985 and the Best Graduate Award in 1996 from Peking University. During his years at the University of Toronto, he received a University of Toronto Open Doctoral Fellowship. In 1997, Dr Qin was awarded NSF CAREER Award from the National Science Foundation (NSF). He is a member of ACM, IEEE and SIAM.

    Arie E. Kaufman is the Director of the Center for Visual Computing (CVC), a Leading Professor and Chair of Computer Science, and Leading Professor of Radiology at the State University of New York at Stony Brook. He was the founding Editor-in-Chief of the IEEE Transaction on Visualization and Computer Graphics (TVCG), 1995–1998. Kaufman has been the co-Chair for the multiple Eurographics/Siggraph Graphics Hardware Workshops, the Papers or Program co-Chair for the IEEE Visualization ’90–’94 and ACM Volume Visualization Symposium ’92, ’94, ’98, and the co-founder and member of the steering committee of the IEEE Visualization conference series. He has previously chaired and is currently a director of the IEEE Computer Society Technical Committee on Computer Graphics. He is the recipient of a 1995 IEEE Outstanding Contribution Award, the 1996 IEEE Computer Society's Golden Core Member, 1998 IEEE Fellow, 1998 ACM Service Award, and 1999 IEEE Computer Society's Meritorious Service Award. Kaufman has conducted research and consulted for about 30 years specializing in volume visualization; graphics architectures, algorithms, and languages; virtual reality; user interfaces; and multimedia. He received a BS in Mathematics and Physics from the Hebrew University of Jerusalem in 1969, an MS in Computer Science from the Weizmann Institute of Science, Rehovot, in 1973, and a PhD in Computer Science from the Ben-Gurion University, Israel, in 1977. For more information see http://www.cs.sunysb.edu/~ari.

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