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<publications>

  <!-- 2007 -->





  <publication>

    <authors> P. Vazquez, C. Andújar </authors>

    <title> Tessellation-Independent Best View Selection </title>

    <where>

      10th International Conference on Computer Graphics and Artificial Intelligence, 3IA'2007, 30-31 May 2007, Athens, Greece

    </where>

    <year> 2007 </year>

    <A href="http://www.lsi.upc.edu/~moving/papers/Tes.pdf">PDF</A>

    <image src="images/papers/Tes.jpg"></image>

    <abstract>

      Automatic selection of good views of 3D models is an important problem with applications in many fields such as scene understanding, imagebased modeling, and scientific data inspection. Most of the view-quality measures proposed so far depend in some way on the geometric representation of object's surface, as they work upon the faces of the model. Thus, most approaches are sensitive to the actual representation or level of detail of the object being analyzed. In this paper we present a new approach for tessellation-independent viewpoint selection. Our method measures the quality of a view by examining the information content of the object's silhouette together with the information content of its depth map, resulting in a metric that overcomes the limitations of previous methods, and provides results more sensitive to human perception.

    </abstract>

  </publication>









  <publication>

    <authors> C. Andújar, F. Argelaguet </authors>

    <title> Virtual Pads: Decoupling Motor Space and Visual Space for Flexible Manipulation of 2D Windows within VEs </title>

    <where>

      Second IEEE Symposium on 3D User Interfaces, 3DUI'07, 10-11 March 2007, Charlotte, NC.

    </where>

    <year> 2007 </year>

    <A href="http://www.lsi.upc.edu/~moving/papers/virtualPads.pdf">PDF</A>

    <image src="images/papers/virtualPads.jpg"></image>

    <abstract>

      The ability to access external 2D applications from within 3D worlds can greatly enhance the possibilities of many VE applications. In this paper we present a new interaction metaphor for fast, accurate and comfortable manipulation of external GUIs displayed as texture-mapped rectangles. The main idea is to decouple the motor space from the visual space so that the external application can be manipulated within a user-defined working volume whose location and size is completely independent from the application's visual representation. This decoupling is accomplished through a virtual pad which receives user actions and maps them into cursor movements. The main advantage of our approach is that both the working space and the visual space can be adjusted independently to suit user preferences. This allows users to seamlessly balance speed and accuracy without affecting the visual representation of the application's GUI. We have implemented an interaction technique adopting our metaphor in combination with a pointing technique and we have evaluated its effectiveness in terms of task performance and user preference. Our experiments indicate that the proposed technique increases user's comfort while providing dynamic management of speed/accuracy tradeoff.

    </abstract>

  </publication>









  <publication>

    <authors> C. Andújar, J. Boo, P. Brunet, M. Fairen, I. Navazo, P. Vazquez, A. Vinacua </authors>

    <title> Omni-directional Relief Impostors </title>

    <where>

      Computer Graphics Forum, Vol. 26 (3), September 2007, pp. 553-560.

    </where>

    <year> 2007 </year>

    <A href="http://www.lsi.upc.edu/~moving/papers/ORIs.pdf">PDF</A>

    <image src="images/papers/omni.jpg"></image>

    <abstract>

      Relief impostors have been proposed as a compact and high-quality representation for high-frequency detail in 3D models. In this paper we propose an algorithm to represent a complex object through the combination of a reduced set of relief maps. These relief maps can be rendered with very few artifacts and no apparent deformation from any view direction. We present an efficient algorithm to optimize the set of viewing planes supporting the relief maps, and an image-space metric to select a sufficient subset of relief maps for each view direction. Selected maps (typically three) are rendered based on the well-known ray-height-field intersection algorithm implemented on the GPU. We discuss several strategies to merge overlapping relief maps while minimizing sampling artifacts and to reduce extra texture requirements. We show that our representation can maintain the geometry and the silhouette of a large class of complex shapes with no limit in the viewing direction. Since the rendering cost is output sensitive, our representation can be used to build a hierarchical model of a 3D scene.

    </abstract>

  </publication>



  <publication>

    <authors> C. Andújar, F. Argelaguet </authors>

    <title> Anisomorphic ray-casting manipulation for interacting with 2D GUIs </title>

    <where> Computers and Graphics, 31(1), January 2007, Pages 15-25 </where>

    <year> 2007 </year>

    <A href="http://www.lsi.upc.edu/~moving/papers/Aniso.pdf">PDF</A>

    <image src="images/papers/ani.jpg"></image>

    <abstract>

      The accommodation of conventional 2D GUIs with Virtual Environments (VEs) can greatly enhance the possibilities of many VE applications. In this paper we present a variation of the well-known raycasting technique for fast and accurate selection of 2D widgets over a virtual window immersed into a 3D world. The main idea is to provide a new interaction mode where hand rotations are scaled down so that the ray is constrained to intersect the active virtual window. This is accomplished by changing the control-display ratio between the orientation of the user’s hand and the ray used for selection. Our technique uses a curved representation of the ray providing visual feedback of the orientation of both the input device and the selection ray. We have implemented this technique and evaluated its effectiveness in terms of performance and user preference. Our experiments on a four-sided CAVE indicate that the proposed technique can increase the speed and accuracy of component selection in 2D GUIs immersed into 3D worlds.

    </abstract>

  </publication>







  <!-- 2006 -->

	<publication>

		<authors> C. Andújar, M. Fairén, F. Argelaguet </authors>

		<title> A Cost-effective Approach for Developing Application-control GUIs for Virtual Environments </title>

		<where> First IEEE Symposium on 3D User Interfaces, 3DUI'06, 25-26 March, Alexandria, VA  pp 847-857. </where>

		<year> 2006 </year>

		<A href="http://www.lsi.upc.edu/~moving/papers/Cost.pdf">PDF</A>

		<image src="images/papers/3dui.jpg"></image>

		<abstract> 

	This paper presents a new approach for fast development of application-control User Interfaces (UIs) for Virtual Environments (VEs). This approach allows developers to build sophisticated UIs containing both simple widgets (such as windows, buttons, menus and sliders) and advanced widgets (such as hierarchical views and web browsers) with minimum effort. Rather than providing a new API for defining and managing the interface components, we propose to extend current 2D toolkits such as Qt so that its full range of widgets can be displayed and manipulated either as 2D shapes on the desktop or as textured 3D objects within the virtual world. This approach allows 3D UI developers to take advantage of the increasing number of components, layout managers and graphical design tools provided by 2D UI toolkits. Resulting programs can run on platforms ranging from fully immersive systems to generic desktop workstations with little or no modification. The design of the system and the key features required on the host UI toolkit are presented and discussed. A prototype system has been implemented above Qt and evaluated on a 4-sided CAVE. The results indicate that this approach provides an efficient and cost-effective way for porting and developing application-control GUIs on VEs and thus it can greatly enhance the possibilities of many VE applications. 

	</abstract>

	</publication>

	

	

		<publication>

		<authors> C. Andújar, F. Argelaguet </authors>

		<title> Friction surfaces: scaled ray-casting manipulation for interacting with 2D GUIs  </title>

		<where> 12th Eurographics Symposium on Virtual Environments, Lisbon, Portugal </where>

		<year> 2006 </year>

		<A href="http://www.lsi.upc.edu/~moving/papers/Friction.pdf">PDF</A>

		<image src="images/papers/friction.jpg"></image>

		<abstract> 

	The accommodation of conventional 2D GUIs with Virtual Environments (VEs) can 

greatly enhance the possibilities of many VE applications. In this paper we 

present a variation of the well-known ray-casting technique for fast and 

accurate selection of 2D widgets over a virtual window immersed into a 3D world. 

The main idea is to provide a new interaction mode where hand rotations are 

scaled down so that the ray is constrained to intersect the active virtual 

window. This is accomplished by changing the control-display ratio between the 

orientation of the user s hand and the ray used for selection. Our technique 

uses a curved representation of the ray providing visual feedback of the 

orientation of both the input device and the selection ray. The users  feeling 

is that they control a flexible ray that gets curved as it moves over a virtual 

friction surface defined by the 2D window. We have implemented this technique 

and evaluated its effectiveness in terms of accuracy and performance. Our 

experiments on a four-sided CAVE indicate that the proposed technique can 

increase the speed and accuracy of component selection in 2D GUIs immersed into 

3D worlds.

	</abstract>

	</publication>









	<!-- 2005 -->

	<publication>

		<authors> C. Andújar, P. Brunet, A. Chica, I. Navazo, J. Rossignac, A. Vinacua </authors>

		<title> Optimizing the topological and combinational complexity of isosurfaces </title>

		<where> Computer-Aided Design,  37 (8),  pp. 847-857, </where>

		<year> 2005 </year>

		<A href="papers/Minimac.pdf">PDF</A>

		<image src="images/papers/Minimac.jpg"></image>

		<abstract> 

	Since the publication of the original Marching Cubes algorithm, numerous variations have been proposed

for guaranteeing water-tight constructions of triangulated approximations of isosurfaces. Most

approaches divide the 3D space into cubes that each occupy the space between eight neighboring samples

of a regular lattice. The portion of the isosurface inside a cube may be computed independently

of what happens in the other cubes, provided that the constructions for each pair of neighboring cubes

agree along their common face. The portion of the isosurface associated with a cube may consist of one

or more connected components, which we call sheets. The topology and combinatorial complexity of

the isosurface is influenced by three types of decisions made during its construction: (1) how to connect

the four intersection points on each ambiguous face, (2) how to form interpolating sheets for cubes with

more than one loop, and (3) how to triangulate each sheet. To determine topological properties, it is

only relevant whether the samples are inside or outside the object, and not their precise value, if there

is one. Previously reported techniques make these decisions based on local -per cube- criteria, often

using precomputed look-up tables or simple construction rules. Instead, we propose global strategies for

optimizing several topological and combinatorial measures of the isosurfaces: triangle count, genus, and

number of shells. We describe efficient implementations of these optimizations and the auxiliary data

structures developed to support them.

	</abstract>

	</publication>

	<!-- 2004 -->

	<publication>

		<authors> Carlos Andújar, Pere Vàzquez, Marta Fairén </authors>

		<title> Way-Finder: guided tours through complex walkthrough models </title>

		<where> Computer Graphics Forum,  23 (3),  pp. 499-508, </where>

		<year> 2004 </year>

		<A href="papers/WayFinder.pdf">PDF</A>

		<!--<A href="http://www.upc.edu/slides.pdf">Slides</A>

	<A href="http://www.upc.edu/slides.pdf">Bibtex</A> 

	-->

		<image src="images/papers/WayFinder.jpg"></image>

		<abstract> 

The exploration of complex walkthrough models is often a difficult task due to the presence of densely occluded

regions which pose a serious challenge to online navigation. In this paper we address the problem of algorithmic

generation of exploration paths for complex walkthrough models.We present a characterization of suitable properties

for camera paths and we discuss an efficient algorithm for computing them with little or no user intervention.

Our approach is based on identifying the free-space structure of the scene (represented by a cell and portal graph)

and an entropy-based measure of the relevance of a view-point. This metric is key for deciding which cells have to

be visited and for computing critical way-points inside each cell. Several results on different model categories are

presented and discussed.

	</abstract>

	</publication>

	<publication>

		<authors> C. Andújar, P. Brunet, A. Chica, I. Navazo, J. Rossignac and A. Vinacua </authors>

		<title> Optimal Iso-surfaces </title>

		<where> Computer-Aided Design and Applications,  1 (4),  pp. 503-512, </where>

		<year> 2004 </year>

		<A href="papers/Optimal.pdf">PDF</A>

		<image src="images/papers/optimal.jpg"></image>

		<abstract> 

Since the publication of the original Marching Cubes algorithm, numerous variations have been proposed

for guaranteeing water-tight constructions of triangulated approximations of iso-surfaces. Most

approaches divide the 3D space into cubes that each occupy the space between eight neighboring samples

of a regular lattice. The portion of the iso-surface inside a cube may be computed independently

of what happens in the other cubes, provided that the constructions for each pair of neighboring cubes

agree along their common face. The portion of the isosurface associated with a cube may consist of

one or more connected components, which we call sheets. We distinguish three types of decisions in

the construction of the iso-surface connectivity: (1) how to split the X-faces, which have alternating

in/out samples, (2) how many sheets to use in a cube, and (3) how to triangulate each sheet. Previously

reported techniques make these decisions based on local criteria, often using precomputed look-up tables

or simple construction rules. Instead, we propose global strategies for optimizing several topological and

combinatorial measures of the iso-surfaces: triangle count, genus, and number of shells. We describe

e_cient implementations of these optimizations and the auxiliary data structures developed to support

them.

	</abstract>

	</publication>

	<publication>

		<authors> Carlos Andújar, Pere Brunet, Antoni Chica, Isabel Navazo, Jarek Rossignac, Alvar Vinacua </authors>

		<title> Computing Maximal Tiles and Application to Impostor-Based Simplification </title>

		<where> Computer Graphics Forum,  23 (3),  pp. 401-410, </where>

		<year> 2004 </year>

		<A href="papers/MaxTilesWeb.pdf">PDF</A>

		<!--<A href="http://www.upc.edu/slides.pdf">Slides</A>

	<A href="http://www.upc.edu/slides.pdf">Bibtex</A> 

	-->

		<image src="images/papers/MaximalTiles.jpg"></image>

		<abstract> 

	The computation of the largest planar region approximating a 3D object is an important problem with wide

applications in modeling and rendering. Given a voxelization of the 3D object, we propose an efficient algorithm

to solve a discrete version of this problem. The input of the algorithm is the set of grid edges connecting the

interior and the exterior of the object (called sticks). Using a voting-based approach, we compute the plane that

slices the largest number of sticks and is orientation-compatible with these sticks. The robustness and efficiency of

our approach rests on the use of two different parameterizations of the planes with suitable properties. The first of

these is exact and is used to retrieve precomputed local solutions of the problem. The second one is discrete and

is used in a hierarchical voting scheme to compute the global maximum. This problem has diverse applications

that range from finding object signatures to generating simplified models. Here we demonstrate the merits of the

algorithm for efficiently computing an optimized set of textured impostors for a given polygonal model.

</abstract>

	</publication>

	<!-- 2003 -->

	<publication>

		<authors> Carlos Andújar, Marta Fairén, Pere Brunet, Victor Cebollada </authors>

		<title> Error-bounded Simplification of Topologically-complex Assemblies </title>

		<where> 4th Workshop on Multiresoluion and Geometric Modelling, MINGLE'03, Cambridge </where>

		<year>  2003 </year>

		<!--<A href="c.pdf">PDF</A> -->

		<image src="images/papers/mingle.jpg"></image> 

		<abstract> Not available.

	</abstract>

	</publication>

	<publication>

		<authors> C. Andújar, P. Brunet, J. Esteve, E. Monclús, I. Navazo and A. Vinacua  </authors>

		<title> Robust face recovery for hybrid surface visualization </title>

		<where> 8th International Workshop in Vision, Modeling and Visualization, VMV'03, Munich, Germany </where>

		<year>  2003 </year>

		<!--<A href="c.pdf">PDF</A> -->

		<image src="images/papers/robust-face-recovery.jpg"></image> -->

		<abstract> Not available.

	</abstract>

	</publication>

	<!-- 2002 -->

	<publication>

		<authors>  Carlos Andújar, Dolors Ayala,  Pere Brunet </authors>

		<title> Topology Simplification through Discrete Models </title>

		<where> ACM Transactions on Graphics, 20 (6), pp. 88-105,</where>

		<year> 2002 </year>

		<A href="papers/Topology.pdf">PDF</A>

		<!--<A href="http://www.upc.edu/slides.pdf">Slides</A>

	<A href="http://www.upc.edu/slides.pdf">Bibtex</A> 

	-->

		<image src="images/papers/Topology.jpg"></image>

		<abstract> 

	This paper presents a new approach for generating coarse-level approximations of topologically complex models. Dramatic

topology reduction is achieved by converting a 3D model to and from a volumetric representation. Our approach produces valid,

error-bounded models and supports the creation of approximations that do not interpenetrate the original model, either being

completely contained in the input solid or bounding it. Several simple to implement versions of our approach are presented

and discussed. We show that these methods perform significantly better than other surface-based approaches when simplifying

topologically-rich models such as scene parts and complex mechanical assemblies.

	</abstract>

	</publication>

	<publication>

		<authors> C. Andujar M. Fairen P. Brunet </authors>

		<title> Affordable Immersive Projection System for 3D Interaction </title>

		<where> 1st Ibero-American Symposium on Computer Graphics SIACG'02. Portugal</where>

		<year>  2002 </year>

		<A href="papers/SIACG-02.pdf">PDF</A>

		<image src="images/papers/SIACG-02.jpg"></image>

		<abstract> This paper describes an affordable Virtual Reality system designed and developed by a group of researchers

at the Polytechnic University of Catalunya (UPC). The system allows direct selection and manipulation of

virtual 3D objects. The interaction is based on stereoscopic images projected over the user's working space

and on devices tracking the user's natural movements. The system includes a screen being adjustable both

in orientation and height, sensors tracking the head and hand movements, and a tactile device for the

forefinger providing touch sense. A prototype of the system is currently exhibited at the Virtual Reality

Center of Barcelona and it is being used in different application fields like architecture, medicine and

industrial design.

	

	</abstract>

	</publication>

	<!-- 2001-->

	<!-- 2000-->

	<publication>

		<authors> Carlos Andújar, Carlos Saona, Isabel Navazo, Pere Brunet </authors>

		<title> Integrating Occlusion Culling and Levels of Detail through Hardly-Visible Sets </title>

		<where> Computer Graphics Forum 19(3) </where>

		<year>  2000 </year>

		<!--<A href="c.pdf">PDF</A> -->

		<image src="images/papers/na.jpg"></image> 

		<abstract> Not available.

	</abstract>

	</publication>

	<publication>

		<authors> Carlos Andújar, Carlos Saona, Isabel Navazo </authors>

		<title> LOD Visibility Culling and Occluder Synthesis  </title>

		<where> Computer-Aided Design 32(13) </where>

		<year>  2000 </year>

		<!--<A href="papers/SIACG-02.pdf">PDF</A> -->

		<image src="images/papers/na.jpg"></image> 

		<abstract>

      Level-of-detail occlusion culling is a novel approach

      to the management of occluders that can be easily

      integrated into most current visibility culling algorithms.

      The main contribution of this paper is

      an algorithm that automatically generates sets of

      densely overlapping boxes with enhanced occlusion

      properties from non-convex subsets. We call this

      method occluder synthesis because it is not sensitive

      to the way the objects are tesselated but to

      the space enclosed by them. The extension of this

      technique by allowing a bounded amount of image

      error is also discussed. We show that visibility

      computations can be based on a multiresolution

      model which provides several representations

      of these occluders with varying visibility accuracy.

      Our tests show that occlusion performance in tesselated

      scenes is improved drastically even if no image error

      is allowed.



    </abstract>

	</publication>

	<!-- anteriores 2000 -->

	<publication>

		<authors> Carlos Andújar </authors>

		<title> Space efficient connectivity test for n-dimensional images  </title>

		<where> Computers and Graphics, 22(4) </where>

		<year>  1998 </year>

		<!--<A href="papers/SIACG-02.pdf">PDF</A> -->

		<image src="images/papers/na.jpg"></image> 

		<abstract> Not available.

	</abstract>

	</publication>

	<publication>

		<authors> Carlos Andújar, Dolors Ayala,  Pere Brunet,  Robert Joan-Arinyo, Jaume Solé </authors>

		<title> Automatic generation of multiresolution boundary representations  </title>

		<where> Computer Graphics Forum 15(3) </where>

		<year>  1997 </year>

		<!--<A href="papers/SIACG-02.pdf">PDF</A> -->

		<image src="images/papers/na.jpg"></image> 

		<abstract> Not available.

	</abstract>

	</publication>

	<publication>

		<authors> Fernando Alonso, Carlos Andújar, Pere Brunet, Luis García, Isabel Navazo, Alvar Vinacua </authors>

		<title> Virtual reality tools in shipbuilding design  </title>

		<where> International Workshop on Collaborative Design, TeamCAD97, GeorgiaTech, Atlanta </where>

		<year>  1997 </year>

		<!--<A href="papers/SIACG-02.pdf">PDF</A> -->

		<image src="images/papers/na.jpg"></image> 

		<abstract> Not available.

	</abstract>

	</publication>

</publications>