%0 Generic %D 2019 %T Architecture of a client-server platform for IMATI cultural heritage applications %A A. Repetto %A C. Catalano %A M. Spagnuolo %K 3D semantic annotation %K Client-server platform %K Cultural heritage %K Geometric similarity %X The final technological outcome of the GRAVITATE EU project is a software platform for the analysis and restoration of cultural heritage artefacts. The GRAVITATE platform is a client-server platform, composed of a back-end infrastructure, of a web interface and a desktop interface. The role of the web interface is to offer browsing and semantic and geometric similarity capabilities, while the desktop client is designed for graphical interaction and manipulation of high-resolution models. Both clients connect to a back-end infrastructure that offers access to 3D models and their geometric properties using a RESTful API. After the end of the project, a work of redesign of the original platform has been carried out, to exploit IMATI applications developed in the project, make them independent of the GRAVITATE servers and services, and putting the basis for future research in the CH domain. This technical report describes the internal organization of the client-server platform that was developed by reusing the parts already developed, and reimplementing the back-end and web interface. The back-end and the web interface were implemented in Python, using the Django framework, while the desktop interface was developed in C++, with the Qt library for the user interface. This technical report describes also the code organization and guides the developer in the task of performing changes and extensions to the platform. %B IMATI Report Series %I CNR-IMATI %C Genova %P 48 %8 07/2019 %G eng %9 Technical Report %0 Generic %D 2019 %T Augmented Reality in manufacturing engineering %A B. Bonino %A F. Giannini %A M. Monti %K 3D object manipulation %K Augmented reality %X The report provides an overview of the existing research works addressing the interaction with 3D models using Augmented Reality technologies. It also illustrates the results of our experiments both simply using HoloLens, Unity 3D and integrating Leap Motion. In the first case, only the built in tap gesture and voice commands have been used for the interaction with the digital elements. Whereas with Leap Motion additional gestures have been considered to easy the 3D digital object manipulation. The carried out experiments reveal the actual limitations of AR technologies for the effective use in real applications merging 3D virtual objects in real environments when digital elements have to be inspected and manipulated. %B IMATI Report Series %I CNR-IMATI %C Genova %P 26 %8 06/2019 %G eng %9 Technical Report %0 Generic %D 2019 %T On expansions and nodes for sparse grid collocation of lognormal elliptic PDEs %A O.G. Ernst %A B. Sprungk %A L. Tamellini %K sparse grids;PDEs with random coefficients;Uncertainty Quant.;Weighted Leja points;Gauss-Hermite points;Levy-Ciesielski exp.;Karhunen-Loeve exp. %X This work is a follow-up on a previous contribution (`Convergence of sparse collocation for functions of countably many Gaussian random variables (with application to elliptic PDEs)' SIAM Journal of Numerical Analysis 2018), and contains further insights on some aspects of the solution of elliptic PDEs with lognormal diffusion coefficients using sparse grids. Specifically, we first focus on the choice of univariate interpolation rules, advocating the use of Gaussian Leja points as introduced by Narayan and Jakeman in 2014 (`Adaptive Leja sparse grid constructions for stochastic collocation and high-dimensional approximation', SIAM Journal on Scientific Computing) and then discuss the possible computational advantages of replacing the standard Karhunen-Loeve expansion of the diffusion coefficient with the Levy-Ciesielski expansion, motivated by theoretical work of Bachmayr, Cohen, DeVore, and Migliorati in 2016 (`Sparse polynomial approximation of parametric elliptic PDEs. part II: lognormal coefficients' ESAIM Mathematical Modelling and Numerical Analysis, 2016). %B IMATI Report Series %I CNR-IMATI %C Pavia %P 34 %8 06/2019 %G eng %9 Preprint %0 Generic %D 2019 %T Parametric shape optimization for combined additive- subtractive manufacturing %A C. Altenhofen %A M. Attene %A O. Barrowclough %A M. Chiumenti %A M. Livesu %A F. Marini %A M. Martinelli %A V. Skytt %A L. Tamellini %K Additive manufacturing %K parametric shape optimization %X In the industrial practice, additive manufacturing processes are often followed by post-processing operations such as subtractive machining, milling, etc. to achieve the desired surface quality and dimensional accuracy. Hence, a given part must be 3D printed with extra material to enable such finishing phase. This combined additive/subtractive technique can be optimized to reduce manufacturing costs by saving printing time and reducing material and energy usage. In this work, a numerical methodology based on parametric shape optimization is proposed for optimizing the thickness of the extra material, allowing for minimal machining operations while ensuring the finishing requirements. Moreover, the proposed approach is complemented by a novel algorithm for generating inner structures leading to reduced distortion and improved weight reduction. The computational effort induced by classical constrained optimization methods is alleviated by replacing both the objective and constraint functions by their sparse-grid surrogates. Numerical results showcase the effectiveness of the proposed approach. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 27 %8 06/2019 %G eng %9 Preprint %0 Generic %D 2019 %T Recognising characteristic elements through the analysis of curves on 3D models %A Chiara Romanengo %A Silvia Biasotti %A Bianca Falcidieno %K characteristic elements %K Feature curves %K Hough transform %X We propose a new method for recognising characteristic curves on 3D shapes, identified by a set of characteristic points. We approximate these curves with known curves, e.g., spirals, their patterns or aggregations, to provide a localisation and quantitative measurement of style features like decorations, visual motifs or anatomical features on the digital models of 3D objects. To solve this problem, we adopt a generalisation of the Hough Transform (HT) which is able to deal with curves represented either in implicit and parametric form and extends the set of curves so far adopted for curve recognition with HT. In addition, we introduce new rules of composition and aggregation of characteristic curves into patterns or decorations, not limiting the recognition to a single curve at a time. Besides planar curves, our method yields the recognition of spatial curves (see Figure 1): to the best of our knowledge, this is the first attempt to apply the HT to the recognition of spatial curves without any projection onto a fitting plane. %B IMATI Report Series %I CNR-IMATI %C Genova %P 24 %8 05/2019 %G eng %9 Preprint %0 Generic %D 2018 %T Adaptive sampling of environmental variables (ASEV) %A S. Berretta %A D. Cabiddu %A S. Pittaluga %A M. Mortara %A M. Spagnuolo %A M. Vetuschi Zuccolini %K Adaptive %K Environmental %K Gaussian Simulation %K Sampling %X In environmental surveys a large sampling effort is required to produce accurate geostatistical maps, representing the distribution of environmental variables and the analysis of each sample is often expensive. The standard way to plan a survey is by non-adaptive sampling, whose distribution is usually completely specified prior to data-collection. In general, the sampling points are located on a regular grid, or along directions that are selected following a priori knowledge. However, the contribution of each point to the final prediction accuracy is typically unknown, and it is likely that lesser points distributed in a different manner might reach the same accuracy results eliminating sampling redundancies. Adaptive sampling uses only few initial sampling points and then follows an iterative collection of data, learning and refining the distribution of the variables in order to optimize the uncertainty of the estimates. In this technical report, we describe the design of an adaptive sampling scheme, where a at each sampling step the next optimal point to be sampled is selected based on: i) an uncertainty map of the environmental parameter distribution, which is continuously updated when a new measure is acquired, and ii) the geometric and physics constraints given by the morphology of the surveyed area. The optimality criterion will take into account the trade-off between cost and prediction precision. This research is funded by the INTERREG-MATRAC-ACP project; its strategic objective is to enhance the protection of marine waters by improved real-time driving of ROVs equipped with a series of digital sensors. The project will lead to the definition of protocols for intervention in emergency situations with minimum risks for human operators, and more efficient monitoring procedures in routine conditions. Before starting experimentation on the field, a simulation study was developed to evaluate the effectiveness of this strategy. %B IMATI Report Series %I CNR-IMATI %C Genova %P 9 %8 08/06/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-06 %9 Technical Report %0 Generic %D 2018 %T Arbitrary-order time-accurate semi-Lagrangian spectral approximations of the Vlasov-Poisson system %A Lorella Fatone %A Daniele Funaro %A Gianmarco Manzini %K high-order methods %K Lagrangian methods %K Vlasov equation %X The Vlasov-Poisson system, modeling the evolution of non-collisional plasmas in the electrostatic limit, is approximated by a Semi-Lagrangian technique. Spectral methods of periodic type are implemented through a collocation approach. Groups of particles are represented by the Fourier Lagrangian basis and evolve, for a single timestep, along an high-order accurate representation of the local characteristic lines. The time-advancing technique is based on Taylor developments that can be, in principle, of any order of accuracy, or by coupling the phase space discretization with high-order accurate Backward Differentiation Formulas (BDF) as in the method-of-lines framework. At each timestep, particle displacements are reinterpolated and expressed in the original basis to guarantee the order of accuracy in all the variables at relatively low costs. Thus, these techniques combine excellent features of spectral approximations with high-order time integration. Series of numerical experiments are performed in order to assess the real performance. In particular, comparisons with standard benchmarks are examined. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 25 %8 26/03/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-01 %0 Generic %D 2018 %T Estimation of the mortality rate functions from time series field data in a stage-structured demographic model for Lobesia botrana %A S. Pasquali %A C. Soresina %K Mortality rate function; stage-structured population; Lobesia botrana %X The estimation of the mortality rate function for a stage-structured population is obtained starting from time-series field data on the abundance of the species. The method is based on the formulation of the mortality as a combination of cubic splines and it is applied to the case of Lobesia botrana, the main pest in the European vineyards, with data collected in a location in the North of Italy. Mortality estimates are based on 3 years of data and are used to obtain the dynamics for two different years. These dynamics give a satisfactory fit of the phenology of the pest. The method presented allows to obtain more flexible shape for the mortality rate functions compared with previously methods applied for the same pest. %B IMATI Report Series %I CNR-IMATI %C Milano %P 15 %8 04/11/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-10 %9 Preprint %0 Generic %D 2018 %T High order VEM on curved domains %A S. Bertoluzza %A M. Pennacchio %A D. Prada %K curved domain %K optimal convergence rate %K Virtual element method %X
We deal with the virtual element method (VEM) for solving the Poisson equation on a domain Ω with curved boundaries. Given a polygonal approximation Ωh of the domain Ω, the standard order m VEM [6], for m increasing, leads to a suboptimal convergence rate. We adapt the approach of [14] to VEM and we prove that an optimal convergence rate can be achieved by using a suitable correction depending on high order normal derivatives of the discrete solution at the boundary edges of Ωh, which, to retain computability, is evaluated after applying the projector Π∇ onto the space of polynomials. Numerical experiments confirm the theory.
%B IMATI Report Series %I CNR-IMATI %C Pavia %P 17 %8 11/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-09 %9 Preprint %0 Generic %D 2018 %T IGA-based Multi-Index Stochastic Collocation for random PDEs on arbitrary domains %A Joakim Beck %A Lorenzo Tamellini %A Raúl Tempone %K combination-technique %K Isogeometric analysis %K multilevel methods %K Sparse grids %K Stochastic Collocation methods %K Uncertainty Quantification %X This paper proposes an extension of the Multi-Index Stochastic Collocation (MISC) method for forward uncertainty quantification (UQ) problems in computational domains of shape other than a square or cube, by exploiting isogeometric analysis (IGA) techniques. Introducing IGA solvers to the MISC algorithm is very natural since they are tensor-based PDE solvers, which are precisely what is required by the MISC machinery. Moreover, the combination-technique formulation of MISC allows the straight-forward reuse of existing implementations of IGA solvers. We present numerical results to showcase the effectiveness of the proposed approach. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 19 %8 25/10/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-08 %9 Preprint %0 Generic %D 2018 %T Multi-criteria similarity assessment for CAD assembly models retrieval %A K. Lupinetti %A F. Giannini %A M. Monti %A J.-P. Pernot %K 3D assembly model retrieval %K Assembly similarity evaluation %K Multiple similarity criteria %K Partial and local similarity %X The use of Digital Mock-Up (DMU) has become mainstream to support the engineering activities all along the Product Design Process. Over the years, companies generated large databases containing digital models and documents related to their products. For instance, considering complex products, the DMU can be composed of several hundred thousand parts assembled together in assembly trees containing tens of sub-assemblies, and representing several terabytes of data. The ability to retrieve existing models is crucial for the competitiveness of companies, as it can help to leverage existing solutions, results and knowledge associated with previous products. To speed up the access to this large amount of reusable information, CAD models search approaches have been proposed, and notably the so-called content-based search techniques which help designers exploiting the implicit knowledge embedded in the models. As part of a system for the retrieval of CAD assembly models, this paper introduces a set of four measures to evaluate assembly similarities according to multiple criteria. These measures are combined to assess three different levels of similarity (local, partial and global). The local measure only considers the contribution of similar parts, while partial and global measures take also into account the number of similar parts compared to the total number of parts in the query and in the target model. Moreover, an ad-hoc visualization interface has been designed to clearly highlight the different similarities and to allow a fast identification of the target models. The validation of the proposed measures is discussed through several academic and industrial examples run on the developed prototype software. %B IMATI Report Series %I CNR-IMATI %C Genova %P 21 %8 08/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-07 %9 Preprint %0 Generic %D 2018 %T Standard per la gestione e procedure di validazione di dati meteo prodotti da sensori eterogenei e distribuiti %A Andrea Clematis %A Brigida Bonino %A Antonella Galizia %K dati non autoritativi %K sensori eterogenei %K standard OGC %K validazione %X Le informazioni meteo in tempo reale rappresentano, in alcune applicazioni, un’informazione essenziale che deve essere nota sia a un pubblico ampio che ai così detti decisori. Negli ultimi anni si è assistito a un notevole sviluppo di reti non ufficiali di osservazione di fenomeni meteo gestite da semplici cittadini. Spesso queste reti utilizzano sensori e strumenti di misura di qualità confrontabile con gli strumenti utilizzati dalle reti ufficiali. La loro disposizione geospaziale rappresenta spesso un’informazione complementare ed importante rispetto alle reti ufficiali. Tuttavia l’integrazione e l’utilizzo di tali dati presenta diversi problemi in vista del loro utilizzo per lo sviluppo di applicazioni a valore aggiunto in sistemi ambientali di vocazione diversa (e.g. geologico, idrologico, meteorologico, oceanico). Il report ha l’obiettivo di fornire un background metodologico e tecnologico per supportare la realizzazione di tali servizi. Nello specifico il report propone una panoramica di nozioni e strumenti per l’accessibilità dei dati raccolti da sensori meteo installati sul territorio e per la loro gestione sia in termini di formati che di servizi forniti dalla comunità scientifica. Viene presentata una rassegna sulle procedure per la validazione di dati da sensore utilizzate nella comunità idro-meteorologica; il report si chiude discutendo alcuni approcci architetturali per l’integrazione dei dati in applicazioni e servizi. %B IMATI Report Series %I CNR-IMATI %C Genova %P 44 %8 10/04/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-03 %0 Generic %D 2018 %T Strumenti e procedure per la gestione e la visualizzazione di dati meteo prodotti da sensori eterogenei e distribuiti tramite interfacce web basate su mappe geografiche %A L. Roverelli %A G. Zereik %A B. Bonino %A A. Galizia %A A. Clematis %K geolocalizzazione %K sensori eterogenei %K sviluppo web %K visualizzazione %XIl report ha lo scopo di fornire un’introduzione rapida e direttamente operativa per lo sviluppo di siti e applicazioni web in grado di gestire e visualizzare informazioni geo localizzate provenienti da sensori (soprattutto meteo) distribuiti sul territorio. Il taglio di questo report è informale e finalizzato a fornire uno strumento di aiuto rapido per lo sviluppo di applicazioni che potranno avere anche un sofisticato contenuto scientifico o tecnologico, ma questo aspetto esula dalle finalità di questo documento.
%B IMATI Report Series %I CNR-IMATI %C Genova %P 59 %8 11/04/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-04 %0 Generic %D 2018 %T A study on 3D shape interaction in virtual reality %A E. Cordeiro %A F. Giannini %A M. Monti %A A. Ferreira %K Immersive environment %K mid-air gestures %K Natural interfaces for shape modelling %X Current immersive modelling environments use non-natural interfaces to support traditional shape modification operations. In the future, we expect that natural interfaces will become the typical interaction method for 3D shape modelling. In this report, we present a study on user gestures and speech interaction for shape modification. With this experiment, we aim to study how users model and manipulate three-dimensional objects in a virtual reality environment through gestures and speech without using any additional device, i.e. no pointer or controller. It will give us a detailed and accurate perception of how users can interact naturally with three-dimensional objects in a virtual reality environment. %B IMATI Report Series %I CNR-IMATI %C Genova %P 22 %8 03/04/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-02 %0 Generic %D 2018 %T TopChart: from functions to quadrangulations %A T. Sorgente %A S. Biasotti %A M. Livesu %A M. Spagnuolo %K Morse theory %K Reeb graphs %K shape analysis %K shape chartification %X We propose a novel algorithm to decompose a 3D object into an atlas of disk-like charts. Decomposition into charts with controlled shape and topology is relevant in many engineering areas, such as spline fitting, compression and re-meshing. We produce our chartifications by jointly exploiting the Reeb graph of a guiding function and its gradient aligned flow paths. The key advancements of our method with respect to similar approaches are: (i) a novel strategy to provably remove all T-junctions; (ii) a stable system to trace flow paths starting far from critical points; (iii) the exploitation of the regularity of certain functions under isometries (e.g., harmonic ones) to produce structurally equivalent chartifications for families of objects posed differently. The charts produced by our system can be of two types: topological quads and topological octagons. Both of them can be easily gridded to produce full quadrilateral meshes, as we demonstrate in the second part of the article. %B IMATI Report Series %I CNR-IMATI %C Genova %P 39 %8 06/2018 %G eng %U http://irs.imati.cnr.it/reports/irs18-05 %9 Preprint %M 18-05 %0 Generic %D 2017 %T Analysis of a multi-ring technique for 3D pattern recognition %A Elia Moscoso Thompson %A Silvia Biasotti %K 3D pattern analysis %K 3D pattern classification %K mesh %X Pattern characterization of geometric features is of great interest in the cultural heritage domain, as the style of the some parts such beards, hairs, helms or cuirass decorations would support and enhance the classification and/or cataloguing of the archaeological artefacts and fragments. In this context, a pattern is a geometric or colour feature which is repeated over a surface, either on its entirety or on a part (for instance, engravings and chisellings, ornamental decorations, etc.). In the literature, methods that face this problem either project the surface into an image and then adopt a image pattern recognition techniques or try to extend in 3D an existing image technique to surfaces. In this paper, we analyse the performance of the technique called mesh Local Binary Pattern (meshLBP) that works on triangulation meshes, considering implementation defined in [WTBdB15, WBdB15] and freely available. Tests are performed on meshes of the repository at STARC - The Cyprus Institute [STA] that correspond to laser scans of earthenware fragments retrieved from the Salamina Island. Fragments are represented with triangulations, not necessarily uniformly sampled. In this paper we analyse two kind of patterns represented by geometric and colorimetric variations on the surface of the fragment. In addition, we discuss a sub-sample strategy to keep the effectiveness of the mesh LBP descriptor and the dependence of the operator on parameters such as the surface representation and the number of rings used for its multi-scale evaluation. Finally, the main limitations of the method are discussed and possible improvements and future developments are outlined. %B IMATI Report Series %I CNR-IMATI %C Genova %P 20 %8 June %G eng %U http://irs.imati.cnr.it/reports/irs17-12 %9 Working paper %0 Generic %D 2017 %T Applying functional principal components to structural topology optimization %A Gianluca Alaimo %A Ferdinando Auricchio %A I. Bianchini %A E. Lanzarone %K Finite Element Analysis %K Functional Principal Components Analysis %K Structural Topology Optimization %X Structural Topology Optimization optimizes the mechanical performance of a structure while satisfying some functional constraints. Nearly all approaches proposed in the literature are iterative, and the optimal solution is found by repeatedly solving a Finite Elements Analysis (FEA). It is thus clear that the bottleneck is the high computational effort, as these approaches require solving the FEA a large number of times. In this work, we address the need for reducing the computational time by proposing a reduced basis method that relies on the Functional Principal Component Analysis (FPCA). The methodology has been validated considering a Simulated Annealing approach for the compliance minimization in a variable thickness cantilever sheet. Results show the capability of FPCA to provide good results while reducing the computational times, i.e., the computational time for a FEA analysis is about one order of magnitude lower in the reduced FPCA space. %B IMATI Report Series %I CNR-IMATI %C Milano %P 26 p. %8 April %G eng %U http://irs.imati.cnr.it/reports/irs17-09 %9 Working paper %1
%0 Generic %D 2017 %T BPX preconditioners for isogeometric analysis using analysis-suitable T-splines %A D. Cho %A R. Vázquez %K BPX-preconditioner %K Optimal multilevel preconditioning %K T-splines %X We propose and analyze optimal additive multilevel solvers for isogeometric discretizations of scalar elliptic problems for locally refined T-meshes. Applying the refinement strategy in Morgenstern and Peterseim, Comput. Aided Geom. Design, 34 (2015), we can guarantee that the obtained T-meshes are p-admissible, which implies that the associated T-splines are analysis suitable. Taking advantage of the multilevel structure of p-admissible T-meshes, we develop a BPX preconditioner on the basis of local smoothing only for the functions affected by a newly added edge by bisection, and prove that our method has optimal complexity. Several numerical experiments confirm our theoretical result and also show the practical performance of the proposed preconditioner. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 32 p. %8 January %G eng %U http://irs.imati.cnr.it/reports/irs17-01 %9 Working paper %0 Generic %D 2017 %T Computational methods for the morphological analysis and annotation of segmented 3D medical data %A G. Patané %A F. Giannini %A M. Attene %K Semantic annotation %K Shape processing %X The document reports some of the main issues related to the semantic annotation of medical data acquired from MRI scans and describes possible solutions. %B IMATI Report Series %I CNR-IMATI %C Genova %P 22 %8 March %G eng %U http://irs.imati.cnr.it/reports/irs17-08 %9 Technical Report %0 Generic %D 2017 %T Convergence of sparse collocation for functions of countably many Gaussian random variables (with application to elliptic PDEs) %A O.G. Ernst %A B. Sprungk %A L. Tamellini %K Best-N -term approximation %K Lognormal diffusion coefficient %K Parameteric PDEs %K Random PDEs %K Sparse grids %K Stochastic collocation %X We give a convergence proof for the approximation by sparse collocation of Hilbert-space-valued functions depending on countably many Gaussian random variables. Such functions appear as solutions of elliptic PDEs with lognormal diffusion coefficients. We outline a general L2-convergence theory based on previous work by Bachmayr et al. (2016) and Chen (2016) and establish an algebraic convergence rate for sufficiently smooth functions assuming a mild growth bound for the univariate hierarchical surpluses of the interpolation scheme applied to Hermite polynomials. We verify specifically for Gauss-Hermite nodes that this assumption holds and also show algebraic convergence w.r.t. the resulting number of sparse grid points for this case. Numerical experiments illustrate the dimension-independent convergence rate. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 30 p. %8 April %G eng %U http://irs.imati.cnr.it/reports/irs17-10 %9 Preprint %0 Generic %D 2017 %T Initial-boundary value problems for nearly incompressible vector fields, and applications to the Keyfitz and Kranzer system %A Anupam P. Choudhury %A Gianluca Crippa %A Laura V. Spinolo %K Initial-boundary value problems %K Keyfitz and Kranzer %K Systems of conservation laws %X We establish existence and uniqueness results for initial boundary value problems with nearly incompressible vector fields. We then apply our results to establish well-posedness of the initial-boundary value problem for the Keyfitz and Kranzer system of conservation laws in several space dimensions. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 19 p. %8 January %G eng %U http://irs.imati.cnr.it/reports/irs17-02 %9 Working paper %0 Generic %D 2017 %T A mathematical model for piracy control through police response %A G.M. Coclite %A M. Garavello %A Laura V. Spinolo %K Crime modeling %K Optimal control %K Piracy %K Reaction-diffusion equations %K Well-posedness %X We introduce a model describing the dynamics and interactions of three populations of ships (pirates ships, commercial cargos, and police watercrafts) in a marine region. We establish well-posedness of the coupled ODE-PDEs system describing the ships dynamics and we discuss a related optimal control problem. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 21 p. %8 February %G eng %U http://irs.imati.cnr.it/reports/irs17-05 %9 Working paper %0 Generic %D 2017 %T Optimality of integrability estimates for advection-diffusion equations %A S. Bianchini %A M. Colombo %A G. Crippa %A Laura V. Spinolo %K Advection-diffusion equation %K Duhamel formula %K integrability estimates and their optimality %K parabolic equations %K self-similar solutions %X We discuss integrability estimates for the solution of an advection-diffusion equation. We first summarize some classical results proving such estimates for certain ranges of the space and time summability of the velocity field. Afterwards we prove the optimality of such ranges by means of new original examples. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 19 p. %8 February %G eng %U http://irs.imati.cnr.it/reports/irs17-04 %9 Working paper %0 Generic %D 2017 %T Quantitative estimates on localised finite differences for the fractional Poisson problem, and applications to regularity and spectral stability %A G. Akagi %A G. Schimperna %A A. Segatti %A Laura V. Spinolo %K Fractional laplacian %K Regularity %K Spectral stability %X We establish new quantitative estimates for localized finite differences of solutions to the Poisson problem for the fractional Laplace operator with homogeneous Dirichlet conditions of solid type settled in bounded domains satisfying the Lipschitz cone regularity condition. We then apply these estimates to obtain (i) regularity results for solutions of fractional Poisson problems in Besov spaces; (ii) quantitative stability estimates for solutions of fractional Poisson problems with respect to domain perturbations; (iii) quantitative stability estimates for eigenvalues and eigenfunctions of fractional Laplace operators with respect to domain perturbations. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 38 p. %8 January %G eng %U http://irs.imati.cnr.it/reports/irs17-03 %9 Working paper %0 Generic %D 2017 %T On the singular local limit for conservation laws with nonlocal fluxes %A M. Colombo %A G. Crippa %A L.V. Spinolo %K Local limit %K Nonlocal conservation law %K Nonlocal continuity equation %K Singular limit %X We give an answer to a question posed in [2], which can be loosely speaking formulated as follows. Consider a family of continuity equations where the velocity field is given by the convolution of the solution with a regular kernel. In the singular limit where the convolution kernel is replaced by a Dirac delta, one formally recovers a conservation law: can we rigorously justify this formal limit? We exhibit counterexamples showing that, despite numerical evidence suggesting a positive answer, one in general does not have convergence of the solutions. We also show that the answer is positive if we consider viscous perturbations of the nonlocal equations. In this case, in the singular local limit the solutions converge to the solution of the viscous conservation law. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 25 %8 2017 %G eng %U http://irs.imati.cnr.it/reports/irs17-14 %9 Preprint %0 Generic %D 2017 %T Soluzioni Open Source per la scalabilità di servizi di raccolta ed utilizzo di dati ambientali da sensore %A Alfonso Quarati %A Andrea Clematis %A Vittorio Levati %K Open Source %K Scalable solutions %K Sensor data %K Web services %X Il documento presenta uno studio sperimentale atto alla valutazione di aspetti di scalabilità di servizi Web sviluppati nell’ambito del progetto TCUBE, mirato alla gestione di grandi quantità di dati eterogenei, dinamici e distribuiti, mediante una piattaforma integrata di servizi per la mobilità nei settori “Trasporti, Territorio e Turismo”. Lo scopo dello studio è stato quello di derivare informazioni qualitative utili alla valutazione del potenziale impatto di alcune delle soluzioni/metodologie adottate nel progetto ed in particolare a quelle relative ad un servizio per la raccolta, trasformazione e sfruttamento di dati provenienti da sensori. Si è effettuata un’indagine sia tecnica che applicativa, finalizzata a supportare lo sviluppo di ulteriori attività progettuali che possano avere come obiettivo la realizzazione di servizi basati su dati metereologici provenienti da reti di sensori e prodotti da o dedicati ad utenti finali. Il presente rapporto propone una sintesi dei risultati di tale attività di analisi, e rappresenta una guida operativa all’applicazione delle diverse tecnologie Open Source adottate, al fine di indirizzarne l’applicazione in contesti territoriali affini e di più ampia scala, quali aree urbane o territori ad alto impatto turistico. %B IMATI Report Series %I CNR-IMATI %C Genova %P 48 p. %8 May %G eng %U http://irs.imati.cnr.it/reports/irs17-11 %9 Technical Report %0 Generic %D 2017 %T A sparse-grid isogeometric solver %A J. Beck %A G. Sangalli %A L. Tamellini %K B-splines %K Combination technique %K Isogeometric analysis %K NURBS %K Sparse grids %X Isogeometric Analysis (IGA) typically adopts tensor-product splines and NURBS as a basis for the approximation of the solution of PDEs. In this work, we investigate to which extent IGA solvers can benefit from the so-called sparse-grids construction in its combination technique form, which was first introduced in the early 90’s in the context of the approximation of high-dimensional PDEs. The tests that we report show that, in accordance to the literature, a sparse grids construction can indeed be useful if the solution of the PDE at hand is sufficiently smooth. Sparse grids can also be useful in the case of non-smooth solutions when some a-priori knowledge on the location of the singularities of the solution can be exploited to devise suitable non-equispaced meshes. Finally, we remark that sparse grids can be seen as a simple way to parallelize pre-existing serial IGA solvers in a straightforward fashion, which can be beneficial in many practical situations. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 24 %8 09/2017 %G eng %U http://irs.imati.cnr.it/reports/irs17-13 %9 Preprint %0 Generic %D 2017 %T Uncertainty quantification of geochemical and mechanical compaction in layered sedimentary basins %A Ivo Colombo %A Fabio Nobile %A Giovanni Porta %A Anna Scotti %A L. Tamellini %K Random PDEs %K Sedimentary basin modeling %K Sparse grids %K Stochastic Collocation Method %K Uncertainty Quantification %X In this work we propose an Uncertainty Quantification methodology for sedimentary basins evolution under mechanical and geochemical compaction processes, which we model as a coupled, time-dependent, non-linear, monodimensional (depth-only) system of PDEs with uncertain parameters. While in previous works (Formaggia et al. 2013, Porta et al., 2014) we assumed a simplified depositional history with only one material, in this work we consider multi-layered basins, in which each layer is characterized by a different material, and hence by different properties. This setting requires several improvements with respect to our earlier works, both concerning the deterministic solver and the stochastic discretization. On the deterministic side, we replace the previous fixed-point iterative solver with a more efficient Newton solver at each step of the time-discretization. On the stochastic side, the multi-layered structure gives rise to discontinuities in the dependence of the state variables on the uncertain parameters, that need an appropriate treatment for surrogate modeling techniques, such as sparse grids, to be effective. We propose an innovative methodology to this end which relies on a change of coordinate system to align the discontinuities of the target function within the random parameter space. The reference coordinate system is built upon exploiting physical features of the problem at hand. We employ the locations of material interfaces, which display a smooth dependence on the random parameters and are therefore amenable to sparse grid polynomial approximations. We showcase the capabilities of our numerical methodologies through two synthetic test cases. In particular, we show that our methodology reproduces with high accuracy multi-modal probability density functions displayed by target state variables (e.g., porosity). %B IMATI Report Series %I CNR-IMATI %C Pavia %P 25 p. %8 03/2017 %G eng %U http://irs.imati.cnr.it/reports/irs17-06 %9 Working paper %0 Generic %D 2017 %T VVS medical workflows: Definition of a static workflow for part-based annotation of wrist bones and web service oriented architecture for executable workflows %A F. Giannini %A M. Pitikakis %K on-line repositories %K semantic web %K Shape processing %X The report describes the extension of the Digital Shape Workbench version 5 (DSW5) for the inclusion of workflows for the analysis and processing of 3D models obtained from medical imaging data. The VVS Workflow Repository (WR) manages the creation, visualization and execution of shape processing workflows. The considered workflows are of two main categories: static and executable. The first category refers a kind of tutorial workflow/pipeline and is used for sharing expert knowledge e.g. for explaining the steps needed when dealing with a specific process. The second one represents chain of executable web services performing specific pipelines of geometric processing functions. The document describes the adopted architecture and structure for their specification and execution. %B IMATI Report Series %I IMATI-CNR %C Genova %P 41 p. %8 03/2017 %G eng %U http://irs.imati.cnr.it/reports/irs17-07 %9 Working paper %0 Generic %D 2016 %T Algorithms for the implementation of adaptive isogeometric methods using hierarchical splines %A Rafael Vázquez %A E.M. Garau %K adaptive methods %K coarsening %K hierarchical splines %K Isogeometric analysis %K local refinement %X In this article we introduce all the ingredients to develop adaptive isogeometric methods based on hierarchical splines. In particular, we give precise definitions of local refinement and coarsening that, unlike previously existing methods, can be understood as the inverse of each other. We also define simple and intuitive data structures for the implementation of hierarchical splines, and algorithms for refinement and coarsening that take advantage of local information. We complete the paper with some simple numerical tests to show the performance of the data structures and algorithms, that have been implemented in the opensource Octave/Matlab code GeoPDEs. %B IMATI Report Series %I IMATI-CNR %C Pavia %P 37 p. %8 07/2016 %G eng %U http://irs.imati.cnr.it/reports/irs16-08 %9 Working paper %0 Generic %D 2016 %T An appointment scheduling framework to balance the production of blood bags from donation %A S. Baş %A G. Carello %A E. Lanzarone %A S. Yalçindağ %K Blood donation appointment scheduling %K Blood donation system %K Mixer integer linear programming model %K Offline and online procedure %K Production balancing %X Blood is fundamental in several care treatments and surgeries, and plays a crucial role in the health care system. It is a limited resource, as it can be produced only by donors and its shelf life is short; thus, the blood donation (BD) system aims at providing adequate supply of blood bags to transfusion centers and hospitals. An effective collection of blood bags from donors is fundamental for adequately feeding the entire BD system and optimizing blood usage. However, despite its relevance, donation scheduling is only marginally addressed in the literature. In this paper we consider the Blood Donation Appointment Scheduling (BDAS) problem, aiming at balancing the production of the different blood types among days in order to provide a quite constant feeding of blood bags to the BD system. We propose a framework for the appointment reservation that accounts for both booked donors and donors arriving without a reservation. It consists of an offline Mixed Integer Linear Programming (MILP) model for preallocating time slots to blood types, and of an online prioritization policy to assign a preallocated slot when the donor calls to make the reservation. %B IMATI Report Series %I CNR-IMATI %C Milano %P 37 p. %8 June %G eng %U http://irs.imati.cnr.it/reports/irs16-06 %9 Technical Report %0 Generic %D 2016 %T Calcolo di descrittori ibridi geometria-colore per l'analisi di similarità di forme 3D %A A. Raffo %A S. Biasotti %K 3D Shape classification %K 3DShape comparison %K Hybrid geometry-colour shape description %X Il riconoscimento e la classificazione di forme geometriche hanno molteplici applicazioni in grafica computazionale, spaziando dallo sviluppo di search engine all’identificazione di anomalie in modelli medicali orientati al paziente, al design di nuovi farmaci e alla sperimentazione in silico. In tutti questi contesti, il confronto tra forme viene tradotto nel confronto tra descrizioni dell’oggetto. È quindi di fondamentale importanza che una buona descrizione dell’oggetto sia quanto più possibile completa, per risultare univoca, e allo stesso tempo concisa, per poter essere facilmente computabile e confrontabile con altre descrizioni. Inoltre, la descrizione geometrica di un oggetto 3D può essere corredata da informazioni colorimetriche, eventuali annotazioni e/o dati derivanti dalla sua acquisizione/provenienza. Nell’ambito generale del confronto di forme 3D, in questo lavoro si analizza un metodo che utilizza proprietà geometriche e colorimetriche. Rispetto alla implementazione presente nella letteratura, si studia una ottimizzazione del metodo volta a diminuirne la complessità computazionale e di memoria, e si discutono possibili strategie per un futuro miglioramento. %B IMATI Report Series %I IMATI-CNR %C Genova %P 24 %8 June %G eng %U http://irs.imati.cnr.it/reports/irs16-05 %0 Generic %D 2016 %T Comparing methods for the approximation of rainfall fields in environmental applications %A G. Patané %A A. Cerri %A V. Skytt %A S. Pittaluga %A S. Biasotti %A D. Sobrero %A T. Dokken %A M. Spagnuolo %K Precipitation analysis %K Storm tracking %K Surface approximation %X Digital environmental data are becoming commonplace and the amount of information they provide is huge, yet complex to process, due to the size, variety, and dynamic nature of the data captured by sensing devices. The paper discusses an evaluation framework for comparing methods to approximate observed rain data, in real conditions of sparsity of the observations. The novelty brought by this experimental study stands in the geographical area and heterogeneity of the data used for evaluation, aspects which challenge all approximation methods. The Liguria region, located in the north-west of Italy, is a complex area for the orography and the closeness to the sea, which cause complex hydro-meteorological events. The observed rain data are highly heterogeneous: two data sets come from measured rain gathered from two different rain gauge networks, with different characteristics and spatial distribution over the Liguria region; the third data set come from weather radar, with a more regular coverage of the same region but a different veracity. Finally, another novelty of the paper is brought by the proposal of an application-oriented perspective on the comparison. The approximation models the rainfield, whose maxima and their evolution is essential for an effective monitoring of meteorological events. Therefore, we adapt a storm tracking technique to the analysis of the displacement of maxima computed by the different methods. %B IMATI Report Series %I CNR-IMATI %C Genova %P 26 p. %8 February %G eng %U http://irs.imati.cnr.it/reports/irs16-10 %9 Technical Report %0 Generic %D 2016 %T Conceptual design of shapes in Virtual Environments through the re-use of heterogeneous data %A Z. Li %A F. Giannini %A P. Véron %A B. Falcidieno %K Conceptual design %K Heterogeneous data %K Shape and object description %K Virtual Reality %X Today, digital data such as 2D images, 3D meshes and 3D point clouds are widely used to design Virtual Environments (VE). Most of the time, only one type of those multimodal data is used to describe and specify the shapes of the objects. However, a single object can be seen as a combination of components linked with constraints specifying the relationships and the rigid transformations defining their arrangement. Thus, the definition of news methods able to combine any kind of multimodal data in an easy way would allow nonexperts of VE to rapidly mock-up objects and scenes. In this paper, we propose a new shape description model together with its associated constraints toolbox enabling the description of complex shapes from multimodal data. Not only rigid transformations are considered but also scale modifications according to the specified context of the constraint setting. The heterogeneous virtual objects (i.e. composed by scalable multimodal components) then result from the resolution of a constraint satisfaction problem through an optimization approach. The proposed approach is illustrated with examples obtained with our prototype software. %B IMATI Report Series %I CNR-IMATI %C Genova %P 23 p. %8 November %G eng %U http://irs.imati.cnr.it/reports/irs16-17 %9 Working paper %0 Generic %D 2016 %T Defect detection in nanostructures %A D. Carrera %A F. Manganini %A G. Boracchi %A E. Lanzarone %K Defect and Anomaly Detection %K Nanobrous materials %K Quality control %K Smart Manufacturing %K Sparse representations %X Nanoproducts represent a potential growing sector and nanobrous materials are widely requested in industrial, medical and environmental applications. Unfortunately, the production processes at the nanoscale are difficult to control, and produced artifacts often exhibit local defects that prevent their functional properties. We present a fully-automated solution to detect defects in nanobrous materials during their production, yielding smart-manufacturing systems that reduce quality-inspection times and wastes. We analyze SEM images of nanobrous materials and learn, during an initial training phase, a model yielding sparse representations of the structures that characterize correctly produced nanobers. Defects are then detected by analyzing patches in test images and assessing the goodness-of-t of each patch to the learned model. The proposed solution has been successfully validated over 45 images acquired from samples produced by a prototype electrospinning machine. The low computational times indicate that the proposed solution can be adopted for real-time monitoring in an industrial-production scenario. %B IMATI Report Series %I CNR-IMATI %C Milano %P 18 %8 April %G eng %U http://irs.imati.cnr.it/reports/irs16-03 %9 Working paper %0 Generic %D 2016 %T Feature curve identification in archaeological fragments using an extension of the Hough transform %A M.L. Torrente %A S. Biasotti %A B. Falcidieno %K Cultural heritage %K Feature identification %K Hough transform %X The use of computer graphics techniques in cultural heritage (CH) has led to impressive improvements in technologies related to digital acquisition and rendering of 3D CH data. Digitized artefacts are becoming widely available for access and reuse, thus increasing the need of tools able to support comparative shape analysis. As 3D artefacts are often worn, eroded and broken, these tools cannot take advantage of existing methods based on exact matching but they rather require new approaches able to identify partial features in portions of models thus leading to a double partiality of the matching problem, in terms of both features and models In this context, we propose a method based on a novel generalization of the Hough transform technique able to identify and localize semantic features like anatomical features, ornaments, or decorations on digital artefacts or fragments, even if the features are partially damaged or incomplete. The major advantages of using a method based on the Hough transform technique are the relative robustness to noise and the recognition power also in the case of partial features. Our experiments on digital models of real artefacts are encouraging and show the potential of the method, which can work on both 3D meshes and point clouds. %B IMATI Report Series %I CNR-IMATI %C Genova %P 19 %8 July %G eng %U http://irs.imati.cnr.it/reports/irs16-09 %9 Working Paper %0 Generic %D 2016 %T From lesson learned to the refactoring of the DRIHM science gateway for hydro-meteorological research %A D. D’Agostino %A G. Zereik %A E. Danovaro %A L. Roverelli %A A. Clematis %A A. Galizia %K e-Infrastructures %K Hydro-meteorology %K Science gateways %X A full hydro-meteorological (HM) simulation, from rainfall to impact on urban areas, is a multidisciplinary activity which consists in the execution of a workflow composed by complex and heterogeneous model engines. Moreover an extensive set of configuration parameters have to be selected consistently among the models, otherwise the simulation can fail or produce unreliable results. The DRIHM portal is a Web-based science gateway aiming to support HM researchers in designing, executing and managing HM simulations. The first version of the portal was developed during the DRIHM project using the gUSE science gateway toolkit. The lesson we learned is guiding a refactoring process that, together with a review of the most relevant technologies for the development of a science gateway, represent the focus of this paper. Beside the technological aspects, the need of a strong interplay between ICT and other domain-specific communities clearly emerged, together with coherent policies in the management of data, computational resources and software components that represent the ecosystem of a science gateways. %B IMATI Report Series %I CNR-IMATI %C Genova %P 24 p. %8 March %G eng %U http://irs.imati.cnr.it/reports/irs16-07 %9 Working paper %0 Generic %D 2016 %T Identification of patterns of repeated parts in solid objects %A L. Chiang %A F. Giannini %A M. Monti %K BRep models %K Regular pattern detection %K shape analysis %X The feature-based modeling approach for designing a mechanical component has been widely adopted by most CAD modelers to maintain the design intent on models. A set of higher level information is requested to enrich the usual geometrical and topological data, in terms of feature information. A well known example of semantically significant data of this type is represented by the knowledge of the existence of symmetrical arrangements of repeated subparts in CAD models. Because of the information transferring, repeated modifications of the models and different tolerances used by the various CAD systems, these specific data can be lost. In this report, after having provided the necessary mathematical background and the state of art of the existing symmetry detection methods, we propose an approach for retrieving symmetries involving a set of user-selected sub-parts in a given BRep part model. The approach is based on a preliminary analysis of the position of points (centroids), each of them representing one repeated feature; a further examination on the faces of the sub-parts is performed to confirm the existence of symmetric arrangements. We have provided the description for the detection of linear translational, reflectional, and circular translational patterns of repeated sub-parts. %B IMATI Report Series %I CNR-IMATI %C Genova %P 128 p. %8 November %G eng %U http://irs.imati.cnr.it/reports/irs16-14 %9 Technical Report %1
F. Giannini
%0 Generic %D 2016 %T Identification of patterns of repeated parts in solid objects - Part II %A L. Chiang %A F. Giannini %A M. Monti %K BRep models %K Regular pattern detection %K shape analysis %X The work described in this report extends the methods described in the report "Identification of Patterns of Repeated Parts in Solid Objects" ([2]) to deal with CAD assemblies and to the detection of additional types of patterns. Specifically rotational and compound patterns of repeated elements are treated. Therefore, references of all notations, definitions and terms of the objects cited in this report can be found in [2]. The Chapter 1 describes the proposed approach to detect rotational patterns of repeated entities in part model, extending the set of types of patterns considered in [1], [2]. Chapter 2 contains the method proposed for assembly models for the detection of symmetric arrangements on components, considering as repeated elements of the patterns the instances of a part or assembly file. Chapter 3 is dedicated to the introduction of the concept of compound pattern, intended as an improvement of the quality of the symmetry information of a model, obtained by combining the information referred to the patterns of repeated elements. The approach has been described and provided either for part and assembly models. %B IMATI Report Series %I IMATI-CNR %C Genova %P 54 p. %8 11/2016 %G eng %U http://irs.imati.cnr.it/reports/irs16-15 %9 Working paper %0 Generic %D 2016 %T Mapping aesthetic properties to 3D free form shapes through the use of a machine learning based framework %A A. Petrov %A J.-P. Pernot %A F. Giannini %A B. Falcidieno %K Aesthetic Properties %K Declarative Modeling %K Free form surfaces %K Geometric Modeling %K Industrial Design %K Machine Learning Application %X Current production is moving from the mass production concept to the product customization and personalization. Customers are not anymore only buyers. Not only they are becoming actors within the Product Development Process (PDP) but, thanks to new production technologies like 3D printers, they can be both designers and producers. In this scenario, the development of user-friendly design tools is crucial. Declarative approaches are suitable and can address such requirements. They exploit generally understood and shared concepts closer to the way people perceive shapes than to the way shapes are modeled with complex geometric models. To this aim, this paper presents a generic framework for understanding the shape characteristics associated to perceptual/aesthetic properties of 3D free form shapes. This framework is used to investigate whether there is a common judgment to characterize the flatness of surfaces and which are the surface shape characteristics affecting the flatness perception? From the experiments, it results that the size and transition of the surrounding influence the perception of the flatness of a given surface strengthening the classification consistency. %B IMATI Report Series %I CNR-IMATI %C Genova %P 27 p. %8 November %G eng %U http://irs.imati.cnr.it/reports/irs16-16 %9 Working paper %0 Generic %D 2016 %T A new design for the implementation of isogeometric analysis in Octave and Matlab: GeoPDEs 3.0 %A Rafael Vázquez %K Isogeometric analysis %K Matlab %K multipatch domains %K Octave %K structure-preserving discretizations %X GeoPDEs (http://rafavzqz.github.io/geopdes) is an Octave/Matlab package for the solution of partial differential equations with isogeometric analysis, first released in 2010. In this work we present in detail the new design of the package, based on the use of Octave and Matlab classes. Compared to previous versions the new design is much clearer, and it is also more efficient in terms of memory consumption and computational time. %B IMATI Report Series %I IMATI-CNR %C Pavia %P 44 p. %8 04/2016 %G eng %U http://irs.imati.cnr.it/reports/irs16-02 %9 Working paper %0 Generic %D 2016 %T Optimal strategies for a time-dependent harvesting problem %A G.M. Coclite %A M. Garavello %A Laura V. Spinolo %K differential games %K fish harvest %K measured-valued solutions %K Optimal control %X We focus on an optimal control problem, introduced by Bressan and Shen in [5] as a model for fish harvesting. We consider the time-dependent case and we establish existence and uniqueness of an optimal strategy, and sufficient conditions for optimality. We also consider a related differential game that models the situation where there are several competin fish companies and we prove existence of Nash equilibria. From the technical viewpoint, the most relevant point is establishing the uniqueness result. This amounts to prove precise a-priori estimates for solutions of suitable parabolic equations with measure-valued coefficients. All the analysis is developed in the case when the fishing domain is one-dimensional. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 44 p. %8 February %G eng %U http://irs.imati.cnr.it/reports/irs16-01 %9 Working paper %0 Generic %D 2016 %T Optimal-order isogeometric collocation at Galerkin superconvergent points %A M. Montardini %A G. Sangalli %A L. Tamellini %K B-splines %K Collocation method %K Isogeometric analysis %K NURBS %K Superconvergent points %X In this paper we investigate numerically the order of convergence of an isogeometric collocation method that builds upon the least-squares collocation method presented in [1] and the variational collocation method presented in [14]. The focus here is on smoothest B-splines/NURBS approximations, i.e, having global C p-1 continuity for polynomial degree p. In particular, we show that using as collocation points a suitable subset of those considered in [1] (which are related to the Galerkin superconvergence theory) it is possible to achieve optimal L2-convergence for odd degree B-splines/NURBS approximations with a pure collocation scheme, i.e., considering as many collocation points as degrees-of-freedom. The method in [1], instead, is based on a leastsquares formulation due to the fact that the set of collocation points outnumbers the degrees-of-freedom to be computed. We especially highlight that we obtain fourth-order convergence for the L2 and Linfty norm of the error when considering cubic basis functions. Further careful analysis is however needed, since the robustness of the method and its mathematical foundations are still unclear. %B IMATI Report Series %I IMATI-CNR %C Pavia %P 22 p. %8 September %G eng %U http://irs.imati.cnr.it/reports/irs16-13 %9 Working paper %0 Generic %D 2016 %T Persistence-based tracking of rainfall field maxima %A D. Sobrero %A A. Cerri %A S. Biasotti %A S. Pittaluga %A M. Spagnuolo %K Critical points %K Persistence analysis %K Storm tracking %X In this paper we propose a novel methodology for tracking the maxima of rainfall precipitation fields, whose changes in time may give interesting insights on the evolution of storms. Our approach is based on a topological analysis of rainfall data allowing for the extraction of the most prominent, and hence meaningful, rainfall field maxima. Then, an ad-hoc bottleneck matching is used to track the evolution of maxima along multiple time instances. The potential of our method is exhibited through a set of experiments carried out on a collection of observed punctual rainfall data and radar measurements provided by Genova municipality and Regione Liguria. %B IMATI Report Series %I CNR-IMATI %C Genova %P 16 p. %8 July %G eng %U http://irs.imati.cnr.it/reports/irs16-11 %9 Technical Report %0 Generic %D 2016 %T Studio e sviluppo di componenti semantiche riusabili per la progettazione di serious game. Applicazioni all'area edutainment %A A. Repetto %A C.E. Catalano %K Edutainment %K Natural heritage %K Object interaction %K Ontologies %K Semantics %X I serious game sono videogiochi che hanno una finalità primaria diversa da quella del puro divertimento, ad esempio quella di trasmettere dei contenuti educativi, oppure di sensibilizzare il pubblico rispetto a determinate tematiche Con particolare riferimento all’area edutainment, questi giochi contengono al loro interno una grande quantità di conoscenze relative al dominio applicativo. Perché il gioco sia realistico dal punto di vista delle interazioni, tali conoscenze vanno tradotte anche nei comportamenti veri e propri dei personaggi del gioco. In questo lavoro è stata sviluppata una metodologia e opportuni strumenti software che consentono di tradurre tali conoscenze formalizzate usando OWL e RDF in comportamenti veri e propri all’interno del motore di gioco. Il lavoro svolto rappresenta un primo passo nella creazione di componenti riusabili, in cui gli oggetti di gioco sono arricchiti con la conoscenza del dominio e possono essere riutilizzati in contesti differenti, con un notevole abbattimento dei costi per gli attori coinvolti nella realizzazione del gioco stesso (esperti del dominio e sviluppatori di giochi. %B IMATI Report Series %I CNR-IMATI %C Genova %P 12 p. %8 July %G eng %U http://irs.imati.cnr.it/reports/irs16-12 %9 Technical Report %0 Generic %D 2016 %T A study of the state of the art of process planning for additive manufacturing %A M. Livesu %A M. Attene %A M. Spagnuolo %A B. Falcidieno %K 3D printing %K Additive manufacturing %K Process planning %X In the manufacturing industry the term Process Planning (PP) is concerned with determining the sequence of individual manufacturing operations needed to produce a given part or product with a certain machine. In this technical report we propose a preliminary analysis of scientic literature on the topic of process planning for Additive Manufacturing (AM) technologies (i.e. 3D printing). We observe that the process planning for additive manufacturing processes consists of a small set of standard operations (repairing, orientation, supports, slicing and toolpath generation). We analyze each of them in order to emphasize the most critical aspects of the current pipeline as well as highlight the future challenges for this emerging manufacturing technology. %B IMATI Report Series %I CNR-IMATI %C Genova %P 16 p. %8 May %G eng %U http://irs.imati.cnr.it/reports/irs16-04 %9 Technical Report %0 Generic %D 2015 %T Adaptive isogeometric methods with hierarchical splines: error estimator and convergence %A A. Buffa %A C. Giannelli %K Conservation laws %K initial boundary-value problems %K numerical schemes %X The problem of developing an adaptive isogeometric method (AIGM) for solving elliptic second-order partial differential equations with truncated hierarchical B-splines of arbitrary degree and different order of continuity is addressed. The adaptivity analysis holds in any space dimensions. We consider a simple residual-type error estimator for which we provide a posteriori upper and lower bound in terms of local error indicators, taking also into account the critical role of oscillations as in a standard adaptive finite element setting. The error estimates are properly combined with a simple marking strategy to define a sequence of admissible locally rened meshes and corresponding approximate solutions. The design of a refine module that preserves the admissibility of the hierarchical mesh configuration between two consectutive steps of the adaptive loop is presented. The contraction property of the quasi-error, given by the sum of the energy error and the scaled error estimator, leads to the convergence proof of the AIGM. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 30 p. %8 January %G eng %U http://irs.imati.cnr.it/reports/irs15-01 %9 Working paper %0 Generic %D 2015 %T On quasi-interpolation operators in spline spaces %A A. Buffa %A E.M. Garau %A G. Sangalli %K B-splines %K Isogeometric analysis %K Quasi-interpolation %X We propose the construction of a class of L2 stable quasi-interpolation operators onto the space of splines on tensor-product meshes, in any space dimension. The estimate we propose is robust with respect to knot repetition and to knot "vicinity" (up to p+1 knots), so it applies to the most general scenario in which the B-spline functions are known to be well defined. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 16 p. %8 December %G eng %U http://irs.imati.cnr.it/reports/irs15-03 %9 Working paper %0 Generic %D 2015 %T Schaeffer's regularity theorem for scalar conservation laws does not extend to systems %A Laura V. Spinolo %A L. Caravenna %K Conservation laws %K Regularity %K Schaeffer theorem %K Shock formation %X Schaeffer’s regularity theorem for scalar conservation laws can be loosely speaking formulated as follows. Assume that the flux is uniformly convex, then for a generic smooth initial datum the admissible solution is smooth outside a locally finite number of curves in the (t, x) plane. Here the term "generic” is to be interpreted in a suitable sense, related to the Baire Category Theorem. Whereas other regularity results valid for scalar conservation laws with convex fluxes have been extended to systems of conservation laws with genuinely nonlinear characteristic fields, in this work we exhibit an explicit counterexample which rules out the possibility of extending Schaeffer’s Theorem. The analysis relies on careful interaction estimates and uses fine properties of the wave front-tracking approximation. %B IMATI Report Series %I CNR-IMATI %C Pavia %P 47 p. %8 May %U http://irs.imati.cnr.it/reports/irs15-02 %9 Working paper