Emilio Camahort

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.

Multi-viewer gesture-based interaction for omni-directional video

Omni-directional video (ODV) is a novel medium that offers viewers a 360º panoramic recording. This type of content will become more common within our living rooms in the near future, seeing that immersive displaying technologies such as 3D television are on the rise. However, little attention has been given to how to interact with ODV content. We present a gesture elicitation study in which we asked users to perform mid-air gestures that they consider to be appropriate for ODV interaction, both for individual as well as collocated settings. We are interested in the gesture variations and adaptations that come forth from individual and collocated usage. To this end, we gathered quantitative and qualitative data by means of observations, motion capture, questionnaires and interviews. This data resulted in a user-defined gesture set for ODV, alongside an in-depth analysis of the variation in gestures we observed during the study.

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.

Multiresolution 3d rendering on mobile devices

We present a client/server system that is able to display 3D scenes on handheld devices. At the server we extract the geometry that is visible for each client and send it. We also extract texture and material information. The clients, running on mobile devices, use that information to render realistic images. Our geometry extraction algorithm employs multiresolution and view-dependent simplification. We present results of our system running on PocketPC 2003 PDAs.

Jittering reduction in marker-based augmented reality systems

Augmented Reality systems have recently become widely used. This is due to the new open source libraries that have emerged for fast application development. In this paper we address one of the most relevant problems in this type of systems, oscillation in the camera pose estimates. We study the oscillation of a system developed using the ARToolkit library. We apply both average and Kalman filters to stabilize the estimates. Using filter substantially reduces oscillation, thus improving the system’s usability.

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.

Tools for Procedural Generation of Plants in Virtual Scenes

Creating interactive graphics applications that present to the user realistic natural scenes is very difficult. Natural phenomena are very complex and detailed to model, and using traditional modeling techniques takes huge amounts of time and requires skilled artists to obtain good results. Procedural techniques allow to generate complex objects by defining a set of rules and selecting certain parameters. This allows to speed up the process of content creation and also allows to create objects on-the-fly, when needed. On-demand generation of scenes enables the authors to create potentially infinite worlds. This survey identifies the main features of the most used systems that implement procedural techniques to model plants and natural phenomena and discuss usability issues.

A hybrid mutiresolution representation for fast tree modeling and rendering

Abstract We introduce a new representation for modeling and rendering plants and trees. The representation is multiresolution and can be automatically generated and rendered in an efficient way. For the trunk and branches we procedurally build a multiresolution structure that preserves the visual appearance of a tree, when rendered at different levels of detail. For the leaves we build a hierarchy of images by pre-processing the botanical tree structure. Unlike other representations, the visual quality of our representation does not depend on viewing position and direction. Our models can be applied to any computer graphics area that requires modeling outdoor scenes like interactive walkthroughs and fly-by’s, realistic rendering, simulation and computer games.

Procedural Graphics Model and Behavior Generation

Todays virtual worlds challenge the capacity of human creation. Trying to reproduce natural scenes, with large and complex models, involves reproducing their inherent complexity and detail. Procedural generation helps by allowing artists to create and generalize objects for highly detailed scenes. But existing procedural algorithms can not always be applied to existing applications without major changes. We introduce a new system that helps include procedural generation into existing modeling and rendering applications. Due to its design, extensibility and comprehensive interface, our system can handle users objects to create and improve applications with procedural generation of content. We demonstrate this and show how our system can generate both models and behaviours for a typical graphics application.