Alejandro García-Alonso

Solving the collision detection problem

Considers how a happy convergence of factors in the mid 195Os led CEIT and the University of Navarre to team up for an ambitious project. First, we accumulated expertise in the fields of computer graphics, mechanism analysis and solid modeling. Second, the appearance of 3D graphics workstations on the market allowed us to put our experience to work to develop CompAMM (Computer Analysis of Machines and Mechanisms), a general-purpose program to simulate and visualize in real time the kinematic analysis of complex articulated bodies. We got a Hewlett Packard 350 SRX in July 1987 and made our first presentation of the real-time analysis and visualization of 3D mechanisms at an international congress in Seville two months later. Target applications included robotics, vehicles, mechanisms, spaceship manoeuvres, teleoperator training, astronaut motion, and ergonomics inside vehicles.<<ETX>>

A large haptic device for aircraft engine maintainability

The virtual reality for maintainability (Revima) VR system supports maintainability simulation in aeronautics. Within this project we have developed and integrated a haptic device, the large haptic interface for aeronautic maintainability (LHIfAM). We use this device to track hand movements and provide force feedback within the large geometric models that describe aircraft engines. The user movements are the same as those that occur when testing physical mock-ups. An integrated haptic device and VR system for testing aircraft engines reduces development costs and avoids the necessity of physical mock-ups formaintainability.

Simultaneous remote haptic collaboration for assembling tasks

Stand-alone virtual environments (VEs) using haptic devices have proved useful for assembly/disassembly simulation of mechanical components. Nowadays, collaborative haptic virtual environments (CHVEs) are also emerging. A new peer-to-peer collaborative haptic assembly simulator (CHAS) has been developed whereby two users can simultaneously carry out assembly tasks using haptic devices. Two major challenges have been addressed: virtual scene synchronization (consistency) and the provision of a reliable and effective haptic feedback. A consistency-maintenance scheme has been designed to solve the challenge of achieving consistency. Results show that consistency is guaranteed. Furthermore, a force-smoothing algorithm has been developed which is shown to improve the quality of force feedback under adverse network conditions. A range of laboratory experiments and several real trials between Labein (Spain) and Queen’s University Belfast (Northern Ireland) have verified that CHAS can provide an adequate haptic interaction when both users perform remote assemblies (assembly of one user’s object with an object grasped by the other user). Moreover, when collisions between grasped objects occur (dependent collisions), the haptic feedback usually provides satisfactory haptic perception. Based on a qualitative study, it is shown that the haptic feedback obtained during remote assemblies with dependent collisions can continue to improve the sense of co-presence between users with regard to only visual feedback.

Approximation of Optimal Voxel Size for Collision Detection in Maintainability Simulations within Massive Virtual Environments

This paper describes a Collision Method for massive virtual environments composed of millions of triangles. It has been applied in the aeronautics industry for maintainability simulations using virtual aircraft engine mock‐ups. The method performs well and has a good interactive frame rate even when it is used for computing force feedback with haptic devices. Space sorting problems chiefly related to voxel techniques, such as memory requirements and optimal voxel size, have been solved. We use advanced memory structures and hashing techniques. To find the optimal voxel size, several analytical solutions have been proposed and compared. These solutions are based on the performance cost function of the algorithm used. Experiments have been undertaken to verify these analytical solutions.

COMPAMM — A Simple and Efficient Code for Kinematic and Dynamic Numerical Simulation of 3-D Multibody Systems with Realistic Graphics

The theoretical foundations of a 3-D multibody program called COMPAMM (COM-Puter Analysis of Machines and Mechanisms) are presented. Instead of using Euler angles or Euler parameters in order to define the spatial orientation of a rigid body, COMPAMM uses the cartesian coordinates of two or more points and the cartesian components of one or more unit vectors rigidly attached to the body. With this coordinates the constraint equations are quadratic and then the jacobian matrix is a linear function of them, needing for its evaluation far less arithmetic operations than with other methods. In addition to this, the mass matrix in the inertial reference frame is constant and Coriolis or centrifugal forces do not appear in the formulation. COMPAMM has also very advanced interactive and graphical capabilities that are very briefly described in this paper. Finally some examples are presented.

Preserving avatar genuineness in different display media

Our research focuses on enabling users to interact with others using 3D avatars with the same appearance and personality in different media such as the Internet, SMS or television and using different devices such as PCs, MACs, PDAs, mobile phones and televisions. This work’s main contribution is its use of a unique architecture, tested with a contact application, which is compatible with different media. The avatar appearance editor, the animation engine and the 3D models are the same for the different media: TV, SMS and Internet chat.

Towards Adaptive Occlusion Culling Using Camera Coherence

Occlusion culling proves to be useful for the interactive visualization of environments that are not densely occluded. Those which are built up by dense geometric sets like aerospace engines composed of thousands of components and millions of polygons. In first place the convenience of using occlusion culling is studied with a simple scheme. Then improvements are analyzed. The key points to obtain frame rate speed-ups are: a convenient occlusion query scheduling provides the performance required; depth sorting is performed only when camera orientation changes more than a given threshold; coherence reduces the number of occlusion queries posted per frame. It is possible to select the percentage of occlusion queries that will be performed in each frame, from non-conservative schemes up to a conservative one. Furthermore, we propose a small addition to the GPU occlusion queries to perform faster renderings

Collision problem: characteristics for a taxonomy

The collision problem appears within many fields. The specific characteristics that can be identified in different problems lead to the broad set of specialized algorithms that appear in the literature. This paper deals with the first step needed to address the collision problem taxonomy challenge: a survey that compiles and suggests a set of characteristics that could be used to discriminate collision problems, i.e. to generate the taxonomy.

Volume Visualization Tools for Medical Applications in Ubiquitous Platforms

This paper presents three required functionality when volume datasets are aimed to be visualized in ubiquitous platforms: (i) support of segmented volume datasets, (ii) navigation inside the volume and (iii) direct visualization of DICOM datasets. DICOM is the de-facto standard in the medical imaging field. The results shows that these functionalities can be achieved using the Volume Rendering component implemented in X3DOM in several web browsers in different platforms (from desktop computer to tablets and mobile phones).

X3DOM volume rendering component for web content developers

We present a real-time volume rendering component for the Web, which provides a set of illustrative and non-photorealistic styles. Volume data is used in many scientific disciplines, requiring the visualization of the inner data, features for enhancing extracted characteristics or even coloring the volume. The Medical Working Group of X3D published a volume rendering specification. The next step is to build a component that realizes the functionalities defined by the specification. We have designed and built a volume rendering component integrated in the X3DOM framework. This component allows content developers to use the X3D specification. It combines and applies multiple rendering styles to several volume data types, offering a suitable tool for declarative volume rendering on the Web. As we show in the result section, the proposed component can be used in many fields that requires the visualization of multi-dimensional data, such as in medical and scientific fields. Our approach is based on WebGL and X3DOM, providing content developers with an easy and flexible declarative way of sharing and visualizing volumetric content over the Web.