Roberto Vivó

Procedural multiresolution for plant and tree rendering

Modeling and rendering of plants and trees requires generating and processing large numbers of polygons. Geometry simplification methods may be used to reduce the polygon count and obtain a multiresolution representation. However, those methods fail to preserve the visual structure of a tree. We propose a different approach: procedural multiresolution. We build procedural models that reflect a trees visual structure at different resolution levels. The models are based on parametric L-systems. Our method takes a parametric chain representing a tree and generates a new chain with embedded multiresolution information. The algorithm is based on a metric that quantifies the relevance of the branches of a tree. The representation supports efficient geometry extraction and produces good visual results.

Interactive three-dimensional rendering on mobile computer devices

We present a client/server system that is able to display 3D scenes on handheld devices. This kind of devices have important restrictions of memory and computing power. Therefore, we need to limit the amount of geometry sent by the server to each client. We extract the geometry that is visible for each client and send it. The clients render the geometry using the OpenGL ES [10] API. Our geometry extraction algorithm employs multiresolution and view-dependent simplification. We present results of our system running on a software implementation of OpenGL ES that runs on a Pock-etPC 2003.

Camera Calibration Using Two Concentric Circles

We present a simple calibration method for computing the extrinsic parameters (pose) and intrinsic parameters (focal length and principal point) of a camera by imaging a pattern of known geometry. Usually, the patterns used in calibration algorithms are complex to build (three orthogonal planes) or need a lot of features (checkerboard-like pattern). We propose using just two concentric circles that, when projected onto the image, become two ellipses. With a simple mark close to the outer circle, our algorithm can recover the full pose of the camera.

Modelling tree structures using a single polygonal mesh

This paper presents a method to obtain a polygonal mesh representing the ramified structure of a tree. We use a method based on L-systems to model the tree. A refining process is applied once the model of the tree is obtained. Soft transitions are achieved in the areas of the tree where there are divisions. In this way, we avoid the possible superimposition and discontinuity problems in geometry. As a result of this process, a continuous polygonal mesh is obtained. This mesh represents all the branches of the tree, allowing the homogeneous application of textures and algorithms to simplify meshes.

Binary space partitioning trees: a multiresolution approach

Space partitioning techniques are a useful means of organizing geometric models into data structures. Such data structures provide easy and efficient access to a wide range of computer graphics and visualization applications like real time rendering of large databases, collision detection, point classification, etc. Binary space partitioning (BSP) trees are one of the most successful space partitioning techniques, since they allow both object modeling and classification in one single structure. However, with the advent of networked graphics applications, there is an increasing need for multiresolution geometric representations. The paper presents a novel method that extends BSP trees to provide such a representation. The models we present have the advantages of both BSP trees and multiresolution representations. Nodes near the root of the BSP tree store coarser versions of the geometry, while leaf nodes provide the finest details of the representation. We present different algorithms to construct multiresolution BSP trees in 2D. Then we propose extensions of our methods to 3D space.

Web browsing behavior analysis and interactive hypervideo

Processing data on any sort of user interaction is well known to be cumbersome and mostly time consuming. In order to assist researchers in easily inspecting fine-grained browsing data, current tools usually display user interactions as mouse cursor tracks, a video-like visualization scheme. However, to date, traditional online video inspection has not explored the full capabilities of hypermedia and interactive techniques. In response to this need, we have developed SMT2ε, a Web-based tracking system for analyzing browsing behavior using feature-rich hypervideo visualizations. We compare our system to related work in academia and the industry, showing that ours features unprecedented visualization capabilities. We also show that SMT2ε efficiently captures browsing data and is perceived by users to be both helpful and usable. A series of prediction experiments illustrate that raw cursor data are accessible and can be easily handled, providing evidence that the data can be used to construct and verify research hypotheses. Considering its limitations, it is our hope that SMT2ε will assist researchers, usability practitioners, and other professionals interested in understanding how users browse the Web.

Integrating synthetic objects into real scenes

Abstract This paper presents a methodology for integrating synthetic objects into real scenes. We take a set of photographs of the real scene and build a simple image-based model. We use high dynamic range images to build an accurate representation of the lighting in the scene. Then we insert a synthetic object into the model and compute its illumination and shading using the lighting information. Illumination changes produced by the synthetic object are also applied to real-scene objects located nearby. We show how easy it is to achieve photo-realistic results without specialized hardware. Our approach takes advantage of techniques like automatic camera calibration, high dynamic range image capture and image-based lighting.

Using a Virtual Maze Task to Assess Spatial Short-term Memory in Adults.

In this paper, we present the Virtual Maze Task that assesses spatial short-term memory in adults involving physical movement and immersion. For physical movement, we used a real bicycle. For immersion, we used a VR HMD. We compared the exposure to the task using two different interaction types (physical active vs. physical inactive conditions). The performance and sensations of the participants were compared in both conditions. We also compared the performance on the virtual task with classical neuropsychological tests. A total of 89 adults participated in our study. The participants’ ability to learn a route within the Virtual Maze Task was tested. Then, the participants assessed their experience scoring the following aspects: interaction and satisfaction. The data were analyzed and we found no differences in satisfaction and interaction scores between the physical active and the physical inactive conditions. However, the condition used for interaction affected the score obtained in the task. There were also significant effects of gender and/or interaction used in other measures of performance on the task. Finally, the performance on the task correlated with the performance on other classical neuropsychological tests for the assessment of short-term memory and spatial memory.

Advanced displays and natural user interfaces to support learning

ABSTRACT Advanced displays and natural user interfaces (NUI) are a very suitable combination for developing systems to provide an enhanced and richer user experience. This combination can be appropriate in several fields and has not been extensively exploited. One of the fields that this combination is especially suitable for is education. Nowadays, children are growing up playing with computer games, using mobile devices, and other technological devices. New learning methods that use these new technologies can help in the learning process. In this paper, two new methods that use advanced displays and NUI for learning about a period of history are presented. One of the methods is an autostereoscopic system that lets children see themselves as a background in the game and renders the elements in 3D without the need for special glasses; the second method is a frontal projection system that projects the image on a table in 2D and works similarly to a touch table. The Microsoft Kinect© is used in both systems for the interaction. A comparative study to check different aspects was carried out. A total of 128 children from 7 to 11 years old participated in the study. From the results, we observed that the different characteristics of the systems did not influence the childrens acquired knowledge, engagement, or satisfaction. There were statistically significant differences for depth perception and presence in which the autostereoscopic system was scored higher. However, of the two systems, the children considered the frontal projection to be easier to use. We would like to highlight that the scores for the two systems and for all the questions were very high. These results suggest that games of this kind (advanced displays and NUI) could be appropriate educational games and that autostereoscopy is a technology to exploit in their development.

Smart video sensors for 3D scene reconstruction of large infrastructures

This paper introduces a new 3D-based surveillance solution for large infrastructures. Our proposal is based on an accurate 3D reconstruction using the rich information obtained from a network of intelligent video-processing nodes. In this manner, if the scenario to cover is modeled in 3D with high precision, it will be possible to locate the detected objects in the virtual representation. Moreover, as an improvement over previous 2D solutions, having the possibility of modifying the view point enables the application to choose the perspective that better suits the current state of the scenario. In this sense, the contextualization of the events detected in a 3D environment can offer a much better understanding of what is happening in the real world and where it is exactly happening. Details of the video processing nodes are given, as well as of the 3D reconstruction tasks performed afterwards. The possibilities of such a system are described and the performance obtained is analyzed.