Efficient Surgical Cutting with Position-Based Dynamics

Iago Berndt (UFRGS), Rafael P. Torchelsen (UFPel), Anderson Maciel (UFRGS)

In: IEEE Computer Graphics and Applications DOI

Simulations of cuts on deformable bodies have been an active research subject for more than two decades. However, previous works based on finite element methods and mass spring meshes cannot scale to complex surgical scenarios. This article presents a novel method that uses position-based dynamics (PBD) for mesh-free cutting simulation. The proposed solutions include a method to efficiently render force feedback while cutting, an efficient heat diffusion model to simulate electrocautery, and a novel adaptive skinning scheme based on oriented particles

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Visual Analysis of Bike-Sharing Systems

Guilherme N. Oliveira (UFRGS), Jose L. Sotomayor (UFRGS), Rafael P. Torchelsen (UFPel), Cláudio T. Silva (NYU), João L. D. Comba (UFRGS),
In: Computers & Graphics Special Section on SIBGRAPI 2016  DOI

Bike-sharing systems are a popular mode of public transportation, increasing in number and size around the world. Public bike-sharing systems attend to the needs of a large number of commuters while synchronizing to the rhythm of big cities. To better understand the usage of such systems, we introduce an interactive visualization system to explore the dynamics of public bike-sharing systems by profiling its historical dataset. By coordinating a pixel-oriented timeline with a map, and introducing a scheme of partial reordering of time series, our design supports the identification of several patterns in temporal and spatial domains. We take New York City׳s bike-sharing program, Citi Bike, as a use case and implement a prototype to show changes in the system over a period of ten months, ranking stations by different properties, using any time interval in daily and monthly timelines. Different analyses are presented to validate the visualization system as a useful operational tool that can support the staff of bike-sharing programs of big cities in the exploration of such large datasets, in order to understand the commuting dynamics to overcome management problems and provide a better service to commuters.

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A Levels-of-Precision Approach for Simulating Multiple Physics-based Soft Tissues

Daniele Fernandes e Silva (UFRGS), Iago U. Berndt (UFRGS), Rafael Torchelsen (UFPEL), Anderson Maciel (UFRGS),
In: XXIX Conference on Graphics, Patterns, and Images (SIBGRAPI) 2016 DOI

Computer simulation of surgical environments is always oversimplified in terms of physical behavior due to the complexity of the tissues and interactions involved, which cannot be fully simulated in real time. To better manage this trade-off between efficiency and effectiveness, we present a hybrid and adaptive environment that combines a set of methods to achieve higher accuracy and performance. Our approach merges physicsbased deformation methods (Finite Elements and Mass Spring) with a non-physical method (Green Coordinates) to approximate more coarsely the behavior when the focus of the interaction is away, and more precisely during direct interaction. We experimentally demonstrate that the computational complexity of the simulation with our method does not increase with the number of objects being simulated. With our approach, a virtual surgery environment with many dynamic organs can be computed at interactive rates for the first time.

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Real-Time Local Unfolding for Agents Navigation on Arbitrary Surfaces

Iago U. Berndt (UFRGS), Anderson Maciel (UFRGS), Rafael Torchelsen (UFPEL)
In: XXVVIII Conference on Graphics, Patterns, and Images (SIBGRAPI) 2015 DOI

Agents path planning is an essential part of games and crowd simulations. In those contexts they are usually restricted to planar surfaces due to the huge computational cost of mapping arbitrary surfaces to a plane without distortions. Mapping is required to benefit from the lower computational cost of distance calculations on a plane (Euclidean distance) when compared to distances on arbitrary surfaces (Geodesic distance). Although solutions have been presented, none have properly handled non-planar surfaces around the agent. In this paper we present mesh parametrization techniques to unfold the region around the agent allowing to extend to arbitrary surfaces the use of existing path planning algorithms initially designed only for planar surfaces. To mitigate the high computational cost of unfolding the entire surface dynamically, we propose pre-processing stages and massive parallelization, resulting in performances similar to that of using a planar surface. We also present a GPU implementation schema that permits a solution to be computed in real-time allowing agents to navigate on deformable surfaces that require dynamic unfolding of the surface. We present results with over 100k agents to prove the approach practicality.

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Memory-optimized Order-independent Transparency with Dynamic Fragment Buffer

Marilena Maule (UFRGS), Rafael Torchelsen (UFFS), Rui Bastos (NVIDIA), João L. D. Comba (UFRGS)
In: Journal Computers & Graphics 2013 DOI

Exact order-independent transparency (OIT) rendering is memory demanding because it requires per-pixel blending of an unknown number of fragments that need to be stored and sorted before compositing. In this paper, we describe the Dynamic Fragment Bu er (DFB) algorithm, which efficiently manages memory to perform correct compositing for pixels with varying numbers of fragments. We present a collection of experiments that illustrate the advantages of the DFB algorithm with respect to other OIT algorithms, and analyze the impact of the proposed variations.

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Visualizing Running Races Through the Multivariate Time-Series of Multiple Runners

Guilherme Oliveira (UFRGS), João Comba (UFRGS), Rafael Torchelsen (UFFS), Claudio Silva (NYU), Maristela Padilha (IPA)
In: XXVI SIBGRAPI Conference on Graphics Patterns and Images, 2013, Peru

The recent widespread of heart rate (HR) monitors is allowing people to measure body response during and after exercise, which produces a collection of time-series on multivariate aspects, such as heartbeat, speed, geolocation, etc. Such monitoring can be extremely important for people with low fitness levels, since they are susceptible to cardiovascular diseases or other physical injuries when exercising at high heartbeat frequencies. Even though most monitors provide tools to export and display this information for each individual, the ability to visualize the collection of multiple runners in a given running race is mostly unexplored. In this work, we present a design study that aims to support analysis and answer several questions raised by an expert on exercise physiology about a given running race. We describe each visualization design and how they individually, or in collaboration, can be used to reveal interesting aspects of the data. We illustrate our results with use cases that provide evaluation and feedback about the visualization designs proposed.

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Hybrid transparency

Marilena Maule (UFRGS), Rafael Torchelsen (UFFS), Rui Bastos (NVIDIA), João L. D. Comba (UFRGS)
InACM Symposium on Interactive 3D Graphics and Games (I3D), 2013, USA DOI

Hybrid transparency is a novel technique for real-time approximation of order-independent transparency. Our hybrid approach combines an accurate compositing, of a few core transparent layers, with a quick approximation, for the remaining ones. The main advantage is its capability to operate in highly restricted memory without noticeable artifacts. This feature enables its usage with increasing scene complexity and image resolution, which other techniques fail to handle. Hybrid transparency is suitable for high-parallel execution, can be implemented using current GPUs and further improved, with minimal GPU architecture changes. We present quality, memory and performance analyzes and comparisons against the individual techniques, which compose our proposal, the adaptive transparency, and a reference image generated with an exact method. Our results demonstrate that hybrid transparency is able to generate high-quality images with the lowest memory consumption at competitive frame-rates.

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