Interprocess data transfer in ATLAS, a platform for distributed applications

The ATLAS platform strives to make several useful but technically involved mechanisms available to the programmer building applications over it with the least possible effort. These mechanisms include network distribution of cooperating processes, a powerful macro language, a journaling system and fault tolerance in the presence of network failures or node crashes. In this paper we discuss the techniques used in ATLAS to implement data transfer over a network between different machines with the least hassle to the programmer.Postprint (published version

Geometric transformations in octrees using shears

Existent algorithms to perform geometric transformations on octrees can be classified in two families: inverse transformation and address computation ones. Those in the inverse transformation family essentially resample the target octree from the source one, and are able to cope with all the affine transformations. Those in the address computation family only deal with translations, but are commonly accepted as faster than the former ones for they do no intersection tests, but directly calculate the transformed address of each black node in the source tree. This work introduces a new translation algorithm that shows to perform better than previous one when very small displacements are involved. This property is particularly useful in applications such as simulation, robotics or computer animation.Postprint (published version

Volume cardiac SPECT image registration

The registration of cardiac images is relevant for the diagnosis of cardiac pathologies. In the case of SPECT (Single Photon Emission Computer Tomography) datasets, this is difficult because of the low resolution of the images. In this paper we present a new registration method for 3D images with poor resolution. Our method is based on the maximization of the mutual information (MI) using a new interpolation method which significantly improves the result of an MI-based strategy on low resolution images. We also use a different optimization strategy than other MI-based algorithms, typically achieving errors of the order of one pixel. We also discuss experimental results of our method.Postprint (published version

ATLAS, a platform for distributed graphics applications

ATLAS, a platform for developing distributed applications by splitting them into several collaborating processes scattered in a local area network is presented. Although of general use, it has features especially designed for supporting graphics applications. We present its architecture and some aspects of its implementation, and discuss design criteria.Postprint (author’s final draft

Automatic code generation for ATLAS communications drivers

ATLAS is a software development platform created in our Department. Among other benefits, it provides support to easily distribute applications over a network. In these applications, communications issues among the different processes should be faced. Pursuing to isolate application developers from the intricacies of these issues, communication drivers are automatically generated from an interface declaration of each process. This automatic code generation --not unlike the generation of stubs in CORBA from the IDL specification-- is the main topic of this report.Postprint (published version

Heterogeneous distribution in ATLAS

The ATLAS platform allows unsophisticated programmers to include advanced features in their applications with no or very little extra information and effort. These features include network distribution of cooperating processes, a powerful macro-language, a flexible journaling system and some other mechanisms directly related to graphics applications problems. In this report we describe how ATLAS is able to distribute the application processes among different architectures without needing a previous configuration information of the available processes for each architecture.Postprint (published version

Estado del arte de la alineación de imágenes médicas e implementación del algoritmo de alineación clásico basado en la información mutua

La alineación de imágenes cardíacas procedentes de imágenes de medicina nuclear tal como la Tomografía Computerizada por Emisión Única de Positrones (SPECT) constituye un campo de investigación activo dada su importancia en el diagnóstico de cardiopatías. En este reporte presentamos el estado del arte de la alineación de imágenes médicas con énfasis en la alineación de imágenes cardíacas al igual que una aplicación del método de alineación para imágenes SPECT cardíacos usando la información mutua como medida de similitud.Cardiac images registration coming from nuclear medicine like Single Positron Emition Computer Tomography (SPECT) has become an active research field since it is an important tool for the diagnostic of cardiac pathologies. In this report we present the state of the art of medical image registration with emphasis in cardiac images, likewise it is presented an application for registration of SPECT images using mutual information like similarity measure.Postprint (published version

Piecewise algebraic surface computation and fairing from a discrete model

This paper describes a constrained fairing method for implicit surfaces defined on a voxelization. This method is suitable for computing a closed smooth surface that approximates an initial set of face connected voxels.Preprin

Syntactic and semantic analysis for extended feedback on computer graphics assignments

©2020 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Modern computer graphics courses require students to complete assignments involving computer programming. The evaluation of student programs, either by the student (self-assessment) or by the instructors (grading) can take a considerable amount of time and does not scale well with large groups. Interactive judges giving a pass/fail verdict do constitute a scalable solution, but they only provide feedback on output correctness. In this article, we present a tool to provide extensive feedback on student submissions. The feedback is based both on checking the output against test sets, as well as on syntactic and semantic analysis of the code. These analyses are performed through a set of code features and instructor-defined rubrics. The tool is built with Python and supports shader programs written in GLSL. Our experiments demonstrate that the tool provides extensive feedback that can be useful to support self-assessment, facilitate grading, and identify frequent programming mistakes.This work has been partially funded by the Spanish Ministry of Economy and Competitiveness and FEDER Grant TIN2017-88515-C2-1-R.Peer ReviewedPostprint (author's final draft

3D model deformations with arbitrary control points

Cage-based space deformations are often used to edit and animate images and geometric models. The deformations of the cage are easily transferred to the model by recomputing fixed convex combinations of the vertices of the cage, the control points. In current cage-based schemes the configuration of edges and facets between these control points affects the resulting deformations. In this paper we present a family of similar schemes that includes some of the current techniques, but also new schemes that depend only on the positions of the control points. We prove that these methods afford a solution under fairly general conditions and result in an easy and flexible way to deform objects using freely placed control points, with the necessary conditions of positivity and continuity.Peer ReviewedPostprint (author's final draft