CRS4 Articolo

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Sketching 3D animations
(Wiley, 1995-09) Balaguer, Jean-Francis; Gobbetti, Enrico
We are interested in providing animators with a general-purpose tool allowing them to create animations using straight-ahead actions as well as pose-to-pose techniques. Our approach seeks to bring the expressiveness of real-time motion capture systems into a general-purpose multi-track system running on a graphics workstation. We emphasize the use of high-bandwidth interaction with 3D objects together with specific data reduction techniques for the automatic construction of editable representations of interactively sketched continuous parameter evolution. In this paper, we concentrate on providing a solution to the problem of applying data reduction techniques in an animation context. The requirements that must be fulfilled by the data reduction algorithm are analyzed. From the Lyche and Moerken knot removal strategy, we derive an incremental algorithm that computes a B-spline approximation to the original curve by considering only a small piece of the total curve at any time. This algorithm allows the processing of the user's captured motion in parallel with its specification, and guarantees constant latency time and memory needs for input motions composed of any number of samples. After showing the results obtained by applying our incremental algorithm to 3D animation paths, we describe an integrated environment to visually construct 3D animations, where all interaction is done directly in three dimensions. By recording the effects of user's manipulations and taking into account the temporal aspect of the interaction, straight-ahead animations can be defined. Our algorithm is automatically applied to continuous parameter evolution in order to obtain editable representations. The paper concludes with a presentation of future work.
Animating Spaceland
(IEEE, 1996-08-29) Balaguer, Jean-Francis; Gobbetti, Enrico
Modern 3D animation systems let a growing number of people generate increasingly sophisticated animated movies, frequently for tutorials or multimedia documents. However, although these tasks are inherently three dimensional, these systems' user interfaces are still predominantly two dimensional. This makes it difficult to interactively input complex animated 3D movements. We have developed Virtual Studio, an inexpensive and easy-to-use 3D animation environment in which animators can perform all interaction directly in three dimensions. Animators can use 3D devices to specify complex 3D motions. Virtual tools are visible mediators that provide interaction metaphors to control application objects. An underlying constraint solver lets animators tightly couple application and interface objects. Users define animation by recording the effect of their manipulations on models. Virtual Studio applies data-reduction techniques to generate editable representations of each animated element that is manipulated.
Head-tracked stereo viewing with two-handed 3D interaction for animated character construction
(Wiley, 1996-09) Turner, Russell; Gobbetti, Enrico; Soboroff, Ian
In this paper, we demonstrate a new interactive 3D desktop metaphor based on two-handed 3D direct manipulation registered with head-tracked stereo viewing. In our configuration, a six-degree-of-freedom head-tracker and CrystalEyes shutter glasses are used to produce stereo images that dynamically follow the user head motion. 3D virtual objects can be made to appear at a fixed location in physical space which the user may view from different angles by moving his head. The user interacts with the simulated 3D environment using both hands simultaneously. The left hand, controlling a Spaceball, is used for 3D navigation and object movement, while the right hand, holding a 3D mouse, is used to manipulate through a virtual tool metaphor, the objects appearing in front of the screen because of negative parallax. In this way, both incremental and absolute interactive input techniques are provided by the system. Hand-eye coordination is made possible by registration between virtual and physical space, allowing a variety of complex 3D tasks to be performed more easily and more rapidly than is possible using traditional interactive techniques. The system has been tested using both Polhemus Fastrak and Logitech ultrasonic input devices for tracking the head and 3D mouse.
Phase Shift Plus Interpolation: a scheme for high performance echo-reconstructive imaging
(American Institute of Physics, 1998) Bonomi, Ernesto; Brieger, Leesa; Nardone, Carlo; Pieroni, Enrico
Echo-reconstruction techniques for non-intrusive imaging have wide application, from subsurface and underwater imaging to medical and industrial diagnostics. The techniques are based on experiments in which a collection of short acoustic or electromagnetic impulses, emitted at the surface, illuminate a certain volume and are backscattered by inhomogeneities of the medium. The inhomogeneities act as reecting surfaces or interfaces which cause signal echoing; the echoes are then recorded at the surface and processed through a "computational lens" defined by a propagation model to yield an image of the same inhomogeneities. The most sophisticated of these processing techniques involve simple acoustic imaging in seismic exploration, for which the huge data sets and stringent performance requirements make high performance computing essential. Migration, based on the scalar wave equation, is the standard imaging technique for seismic applications [1]. In the migration process, the recorded pressure waves are used as initial conditions for a wave field governed by the scalar wave equation in an inhomogeneous medium. Any migration technique begins with an a priori estimate of the velocity field obtained from well logs and an empirical analysis of seismic traces. By interpreting migrated data, comparing the imaged interfaces with the discontinuities of the estimated velocity model, insuficiencies of the velocity field can be detected and the estimate improved [2], allowing the next migration step to image more accurately. The iterative process (turnaround) of correcting to a velocity model consistent with the migrated data can last several computing weeks, and is particularly crucial for imaging complex geological structures, including those which are interesting for hydrocarbon prospecting. Subsurface depth imaging, being as it is the outcome of repeated steps of 3D seismic data migration, requires Gbytes of data which must be reduced, transformed, visualized and interpreted to obtain meaningful information. Severe performance requirements have led in the direction of high performance computing hardware and techniques. In addition, an enormous effort has historically gone into simplifying the migration model so as to reduce the cost of the operation while retaining the essential features of the wave propagation. The phase-shift-plus-interpolation (PSPI) algorithm can be an effective method for seismic migration using the "one-way" scalar wave equation; it is particularly well suited to data parallelism because of, among other things, its decoupling of the problem in the frequency domain.
Mapping basin scale variable source areas from multitemporal remotely sensed observations of soil moisture behavior
(Wiley, 1998-12) Verhoest, Niko E.C.; Troch, P. A.; Paniconi, Claudio; De Troch, F. P.
Soil moisture is an important and highly variable component of the hydrologic cycle. Active microwave remote sensing offers the potential for frequent observation of soil moisture at basin and regional scales. Notwithstanding recent advances, the goal of obtaining accurate and reliable measurements or maps of soil moisture from these instruments remains elusive. The main difficulties for active sensors such as synthetic aperture radar (SAR) are the combined effects of soil moisture, surface roughness, and vegetation on the backscattered signal. We show that it is possible to separate soil moisture information from the other physical factors that dominate the radar backscattering, such as topography and land cover, through a principal component analysis of a time series of eight European Remote Sensing (ERS) SAR images. The soil moisture patterns observed in one of the principal components are consistent with the rainfall-runoff dynamics of a catchment and reflect the variable source areas occuring in the vicinity of the river network.
Multifractal analysis and simulation of rainfall fields in space
(Elsevier, 1999) Deidda, Roberto
Statistical downscaling of precipitation from the large scales of meteorological models to the characteristic response scales of small catchment basins needs to correctly preserve the anomalous scaling laws observed in real rainfall. Multifractal behaviour of precipitation in space is investigated on a set of rainfall fields obtained by a high resolution simulation with a limited area model for numerical weather prediction and on two sets of radar measures of it rainfall during the GATE campaign. Some sets of synthetic rainfall fields were generated applying a multifractal model based on a wavelet expansion with coefficients extracted by a log-Poisson random cascade, and results of comparisons with the GATE rainfall fields are presented.
Metis: an object-oriented toolkit for constructing virtual reality applications
(Wiley, 1999-06) Turner, Russell; Li, Song; Gobbetti, Enrico
Virtual reality systems provide realistic look and feel by seamlessly integrating three-dimensional input and output devices. One software architecture approach to constructing such systems is to distributethe application between a computation-intensive simulator back-end and a graphics-intensive viewer front-end which implements user interaction. Inthis paper we discuss Metis, a toolkit we have been developing based on such a software architecture, which can be used for building interactiveimmersive virtual reality systems with computationally intense components. The Metis toolkit defines an application programming interface on thesimulator side, which communicates via a network with a standalone viewer program that handles all immersive display and interactivity. Networkbandwidth and interaction latency are minimized, by use of constraint network on the viewer side that declaratively defines much of dynamic andinteractive behavior of the application.
Spatial distribution of chaotic transients in unidirectional synchronization
(Elsevier, 1999-06-28) Santoboni, Giovanni; Bishop, Steven R.; Varone, Alberto
We consider the transient time to synchronisation in unidirectionally coupled dynamical systems, both discrete maps and continuous flows. We note that while in certain systems the time distribution is typical of chaotic transients, in other cases the distribution possesses a specific spatial organization.
Matching techniques to compute image motion
(Elsevier, 2000-02) Giachetti, Andrea
This paper describes a thorough analysis of the pattern matching techniques used to compute image motion from a sequence of two or more images. Several correlation/distance measures are tested, and problems in displacement estimation are investigated. As a byproduct of this analysis, several novel techniques are presented which improve the accuracy of flow vector estimation and reduce the computational cost by using filters, multi-scale approach and mask sub-sampling. Further, new algorithms to obtain a sub-pixel accuracy of the flow are proposed. A large amount of experimental tests have been performed to compare all the techniques proposed, in order to understand which are the most useful for practical applications, and the results obtained are very accurate, showing that correlation-based flow computation is suitable for practical and real-time applications.
Time-critical multiresolution rendering of large complex models
(Elsevier, 2000-11) Gobbetti, Enrico; Bouvier, Eric
Very large and geometrically complex scenes, exceeding millions of polygons and hundreds of objects, arise naturally in many areas of interactive computer graphics. Time-critical rendering of such scenes requires the ability to trade visual quality with speed. Previous work has shown that this can be done by representing individual scene components as multiresolution triangle meshes, and performing at each frame a convex constrained optimization to choose the mesh resolutions that maximize image quality while meeting timing constraints. In this paper we demonstrate that the nonlinear optimization problem with linear constraints associated to a large class of quality estimation heuristics is efficiently solved using an active-set strategy. By exploiting the problem structure, Lagrange multipliers estimates and equality constrained problem solutions are computed in linear time. Results show that our algorithms and data structures provide low memory overhead, smooth level-of-detail control, and guarantee, within acceptable limits, a uniform, bounded frame rate even for widely changing viewing conditions. Implementation details are presented along with the results of tests for memory needs, algorithm timing, and efficacy.
HPF to OpenMP on the Origin2000: a case study
(Wiley, 2000-11-30) Brieger, Leesa
The geophysics group at CRS4 has long developed echo reconstruction codes in HPF on distributed-memory machines. Now, however, with the arrival of shared-memory machines and their native OpenMP compilers, the transfer to OpenMP would seem to present the logical next step in our code development strategy. Recent experience with porting one of our important HPF codes to OpenMP does not bear this out—at least not on the Origin2000. The OpenMP code suffers from the immaturity of the standard, and the operating system's handling of UNIX threads seems to severely penalize OpenMP performance. On the other hand, the HPF code on the Origin2000 is fast, scalable and not disproportionately sensitive to load on the machine.
Exploring virtual prototypes using time-critical rendering techniques
(ERCIM EEIG, 2001-01) Gobbetti, Enrico; Scateni, Riccardo
Scientists at CRS4, the Center for Advanced Studies, Research and Development in Cagliari, Sardinia, Italy, have developed a time-critical rendering algorithm that relies upon a scene description in which objects are represented as multiresolution meshes. In collaboration with other European partners, this technique has been applied to the visual and collaborative exploration of large digital mock-ups.
TOM: totally ordered mesh. A multiresolution data structure for time-critical graphics applications
(World Scientific, 2001-01) Gobbetti, Enrico; Bouvier, Eric
Tridimensional interactive applications are confronted to situations where very large databases have to be animated, transmitted and displayed in very short bounded times. As it is generally impossible to handle the complete graphics description while meeting timing constraint, techniques enabling the extraction and manipulation of a significant part of the geometric database have been the focus of many research works in the field of computer graphics. Multiresolution representations of 3D models provide access to 3D objects at arbitrary resolutions while minimizing appearance degradation. We describe the TOM (Totally Ordered Mesh), a multiresolution triangle mesh structure tailored to the support of time-critical adaptive rendering. The structure grants high speed access to the continuous levels of detail of a mesh and allows very fast traversal of the list of triangles at arbitrary resolution so that bottlenecks in the graphic pipeline are avoided. Moreover, and without specific compression, the memory footprint of the TOM is small (about 108% of the single resolution object in face-vertex form) so that large scenes can be handled effectively. The TOM structure also supports storage per vertex (or per corner of triangle) attributes such as colors, normals, texture coordinates or dynamic properties. Implementation details are presented along with the results of tests for memory needs, approximation quality, timing and efficacy.
Modeling and Analysis of Seawater Intrusion in the Coastal Aquifer of Eastern Cap-Bon, Tunisia
(Kluwer, 2001-04) Paniconi, Claudio; Khlaifi, Ihsen; Lecca, Giuditta; Giacomelli, Andrea; Tarhouni, Jamila
A numerical model that treats density-dependent variably saturated flow and miscible salt transport is used to investigate the occurrence of seawater intrusion in the ‘Korba’ aquifer of the eastern coast of Cap-Bon in northern Tunisia. We examine the interplay between pumping regimes and recharge scenarios and its effect on the saline water distribution. More localized simulations are used to examine, in vertical cross sections, the effects of well location and soil type and the role of the vadose zone in possible remediation actions. The exploratory simulations suggest interesting interactions between the unsaturated zone and the saltwater–freshwater interface with possible implications for groundwater exploitation from shallow unconfined coastal aquifers, involving in one case feedback between seawater intrusion and the high pressure head gradients around the pumping-induced drawdown cone and in another case threshold-like interface displacement for tight soils such as clays. The data processing steps undertaken in this GIS and modeling study are described in some detail, and a critical assessment is given of the data availability and of the requirements for successful monitoring and modeling of seawater intrusion risks in heavily exploited coastal aquifers such as those found in the semi-arid regions of the Mediterranean basin. It is shown how, with the aid of GIS, reasonably reliable information can be assembled from maps, surveys, and other sources of geospatial and hydrogeological data, an approach that is necessary in the many regions of the world with acute water resource problems but with limited means for undertaking systematic data acquisition and environmental monitoring actions. Nonetheless the need for more concerted monitoring of relevant parameters and processes and of closer coordination between monitoring and modeling is stressed. An idea of the extent of over-exploitation of the Korba aquifer is obtained by examining the pumping and rainfall/infiltration data, and the simulation results support groundwater pumping as the mechanism for and seawater intrusion as the origin of the salt contamination observed in the soils and subsurface waters of the Korba plain.
A conceptual framework for multi-modal interactive virtual workspaces
(2001-11) Aspin, Rob; Da Dalto, Laurent; Fernando, Terrence; Gobbetti, Enrico; Marache, Mathieu; Shelbourn, Mark; Soubra, Souheil
Construction projects involve a large number of both direct stakeholders (clients, professional teams, contractors, etc.) and indirect stakeholders (local authorities, residents, workers, etc.). Current methods of communicating building design information can lead to several types of difficulties (e.g. incomplete understanding of the planned construction, functional inefficiencies, inaccurate initial work or clashes between components, etc.). Integrated software solutions based on VR technologies can bring significant value improvement and cost reduction to the Construction Industry. The aim of this paper is to present research being carried out in the frame of the DIVERCITY project (Distributed Virtual Workspace for Enhancing Communication within the Construction Industry - IST project n°13365), funded under the European IST programme (Information Society Technologies). DIVERCITY's goal is to develop a Virtual Workspace that addresses three key building construction phases: (1) Client briefing (with detailed interaction between clients and architects); (2) Design Review (which requires detailed input from multidisciplinary teams - architects, engineers, facility managers, etc.); (3) Construction (aiming to fabricate or refurbish the building).Using a distributed architecture, the DIVERCITY system aims to support and enhance concurrent engineering practices for these three phases allowing teams based in different geographic locations to collaboratively design, test and validate shared virtual projects. The global DIVERCITY project will be presented in terms of objectives and the software architecture will be detailed.
A multiprocessor decoupled system for the simulation of temporal bone surgery
(Springer, 2002-07) Agus, Marco; Giachetti, Andrea; Gobbetti, Enrico; Zanetti, Gianluigi; Zorcolo, Antonio
A training system for simulating temporal bone surgery is presented. The system is based on patient-specific volumetric object models derived from 3D CT and MR imaging data. Real-time feedback is provided to the trainees via real-time volume rendering and haptic feedback. The performance constraints dictated by the human perceptual system are met by exploiting parallelism via a decoupled simulation approach on a multi-processor PC platform. In this paper, system components are detailed and the current state of the integrated system is presented.
Real-time haptic and visual simulation of bone dissection
(MIT, 2003-02) Agus, Marco; Giachetti, Andrea; Gobbetti, Enrico; Zanetti, Gianluigi; Zorcolo, Antonio
Bone dissection is an important component of many surgical procedures. In this paper, we discuss a haptic and visual simulation of a bone-cutting burr that is being developed as a component of a training system for temporal bone surgery. We use a physically motivated model to describe the burr-bone interaction, which includes haptic forces evaluation, the bone erosion process, and the resulting debris. The current implementation, directly operating on a voxel discretization of patient-specific 3D CT and MR imaging data, is efficient enough to provide real-time feedback on a low-end multiprocessing PC platform.
Reconstruction and web distribution of measurable arterial models
(Elsevier, 2003-03) Giachetti, Andrea; Tuveri, Massimiliano; Zanetti, Gianluigi
In this paper a novel framework for the segmentation, 3D reconstruction and web distribution of vessel structures specifically tailored to the assessment of abdominal aortic aneurysms for endovascular surgery planning is presented. Deformable models are used for segmentation, while VRML97 and ECMA scripting are used to obtain models that are not only viewable from any VRML97 enabled browser, but that also allow users to perform, directly from standard web browsers, guided measurements of geometrical parameters, relevant to surgical planning.
Finite volume/mixed finite element analysis of pollutant transport and bioremediation in heterogeneous saturated aquifers
(Wiley, 2003-04-10) Gallo, Claudio; Manzini, Gianmarco
The adoption of a suitable pumping–injecting well network and the human enhancement of the activity of soil bacteria, whose metabolism contributes to degrade and transform many pollutants in non-toxic substances, may be crucial in the process of remediation of contaminated soils. Organic contaminant transport in a subsurface aquifer and its biological degradation kinetics is numerically addressed by using a four contaminant species model. A numerical approach is proposed, that is based on a cell-centre finite volume method for the system of advection–dispersion equations of contaminants with a mixed-hybrid finite element method for the solution of a single-phase Darcy's equation. The effectiveness of the method and its accuracy in retaining the main physical properties of the continuous mathematical model is illustrated by simulating the time evolution of contaminant concentrations in a set of realistic scenarios.
Numerical simulation of non-Fickian transport in geological formations with multiple-scale heterogeneities
(American Geophysical Union, 2004) Cortis, Andrea; Gallo, Claudio; Scher, Harvey; Berkowitz, Brian
We develop a numerical method to model contaminant transport in heterogeneous geological formations. The method is based on a unified framework that takes into account the different levels of uncertainty often associated with characterizing heterogeneities at different spatial scales. It treats the unresolved, small-scale heterogeneities (residues) probabilistically using a continuous time random walk (CTRW) formalism and the largescale heterogeneity variations (trends) deterministically. This formulation leads to a Fokker-Planck equation with a memory term (FPME) and a generalized concentration flux term. The former term captures the non-Fickian behavior arising from the residues, and the latter term accounts for the trends, which are included with explicit treatment at the heterogeneity interfaces. The memory term allows a transition between non-Fickian and Fickian transport, while the coupling of these dynamics with the trends quantifies the unique nature of the transport over a broad range of temporal and spatial scales. The advection-dispersion equation (ADE) is shown to be a special case of our unified framework. The solution of the ADE is used as a reference for the FPME solutions for the same formation structure. Numerical treatment of the equations involves solution for the Laplace transformed concentration by means of classical finite element methods, and subsequent inversion in the time domain. We use the numerical method to quantify transport in a two-dimensional domain for different expressions for the memory term. The parameters defining these expressions are measurable quantities. The calculations demonstrate long tailing arising (principally) from the memory term and the effects on arrival times that are controlled largely by the generalized concentration flux term.

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