John Congote

Interactive visualization of volumetric data with WebGL in real-time

This article presents and discusses the implementation of a direct volume rendering system for the Web, which articulates a large portion of the rendering task in the client machine. By placing the rendering emphasis in the local client, our system takes advantage of its power, while at the same time eliminates processing from unreliable bottlenecks (e.g. network). The system developed articulates in efficient manner the capabilities of the recently released WebGL standard, which makes available the accelerated graphic pipeline (formerly unusable). The dependency on specially customized hardware is eliminated, and yet efficient rendering rates are achieved. The Web increasingly competes against desktop applications in many scenarios, but the graphical demands of some of the applications (e.g. interactive scientific visualization by volume rendering), have impeded their successful settlement in Web scenarios. Performance, scalability, accuracy, security are some of the many challenges that must be solved before visual Web applications popularize. In this publication we discuss both performance and scalability of the volume rendering by WebGL ray-casting in two different but challenging application domains: medical imaging and radar meteorology.

Realtime Dense Stereo Matching with Dynamic Programming in CUDA

Real-time depth extraction from stereo images is an important process in computer vision. This paper proposes a new implementation of the dynamic programming algorithm to calculate dense depth maps using the CUDA architecture achieving real-time performance with consumer graphics cards. We compare the running time of the algorithm against CPU implementation and demonstrate the scalability property of the algorithm by testing it on different graphics cards.

Real-time depth map generation architecture for 3D videoconferencing

In this paper we present a reliable depth estimation system which works in real-time with commodity hardware. The system is specially intended for 3D visualization using autostereoscopic displays. The core of this work is an implementation of a modified version of the adaptive support-weight algorithm that includes highly optimized algorithms for GPU, allowing accurate and stable depth map generation. Our approach overcomes typical problems of live depth estimation systems such as depth noise and flickering. Proposed approach is integrated within the versatile GStreamer multimedia software platform. Accurate depth map estimation together with real-time performance make proposed approach suitable for 3D videoconferencing.

MEDX3DOM: MEDX3D for X3DOM

We present an implementation of MEDX3DOM a MEDX3D standard implemented into the X3DOM framework. We present the report of a work in progress of the implementation identifying the critical sections to be migrated into the new architecture, and possible extensions of the standard on the Web environment. Results for the early implementation are shown, where the visualization of medical datasets with advanced direct volume rendering algorithms are obtained under the X3DOM architecture with interactive frame rates and good image quality. An example of the HTML5/X3DOM document is presented with future.

Volume Ray Casting in WebGL

Real-time 3D computer graphics systems usually handle surface description models (i.e. B-Rep representations) and use surface rendering techniques for visualization. Common 3D model formats such as VRML, X3D, COLLADA, U3D (some intended for the Web) are based entirely on polygonal meshes or higher order surfaces. Real-time rendering of polygon models is straightforward and raster render algorithms are implemented in most graphics accelerating hardware. For many years several rendering engines, often via installable browser plug-ins, have been available to support 3D mesh visualization in Web applications.

Statistical tuning of adaptive-weight depth map algorithm

In depth map generation, the settings of the algorithm parameters to yield an accurate disparity estimation are usually chosen empirically or based on unplanned experiments. A systematic statistical approach including classical and exploratory data analyses on over 14000 images to measure the relative influence of the parameters allows their tuning based on the number of bad pixels. Our approach is systematic in the sense that the heuristics used for parameter tuning are supported by formal statistical methods. The implemented methodology improves the performance of dense depth map algorithms. As a result of the statistical based tuning, the algorithm improves from 16.78% to 14.48% bad pixels rising 7 spots as per the Middlebury Stereo Evaluation Ranking Table. The performance is measured based on the distance of the algorithm results vs. the Ground Truth by Middlebury. Future work aims to achieve the tuning by using significantly smaller data sets on fractional factorial and surface-response designs of experiments.

Extending Marching Cubes with Adaptative Methods to Obtain More Accurate Iso-surfaces

This work proposes an extension of the Marching Cubes algorithm, where the goal is to represent implicit functions with higher accuracy using the same grid size. The proposed algorithm displaces the vertices of the cubes iteratively until the stop condition is achieved. After each iteration, the difference between the implicit and the explicit representations is reduced, and when the algorithm finishes, the implicit surface representation using the modified cubical grid is more accurate, as the results shall confirm. The proposed algorithm corrects some topological problems that may appear in the discretization process using the original grid.

ReWeb3D: enabling desktop 3D applications to run in the web

Currently, 3D rendering is accessible within Web browsers through open standards such as WebGL, X3D, and X3DOM. At the same time, there is wealth of mature desktop software which comprises algorithms, data structures, user interfaces, databases, etc. It is a challenge to reuse such desktop software using the Web visualization resources. In response to this challenge, this article presents a novel framework, called ReWeb3D, which minimizes the redevelopment for migration of existing 3D applications to the Web. The redeployed application runs on a Web server. ReWeb3D captures low-level graphic calls including geometry, texture, and shader programs. The captured content is then served as a WebGL-enabled web page that conveys full interactivity to the client. By splitting the graphics pipeline between client and server, the workload can be balanced, and high-level implementation details and 3D content are hidden. The feasibility of ReWeb3D has been tested with applications which use OpenSceneGraph as rendering platform. The approach shows good results for applications with large data sets (e.g. geodata), but is less suited for applications intensive in animations (e.g. games).