Call for Papers: Special Section on Computational Fabrication

We are very pleased to announce a Special Section on Computational Fabrication for the Computers and Graphics Journal. The Computers and Graphics Journal is ranked as one of the top four venues in Computer Graphics and has developed a reputation for quality and speed. For this Special Section, we seek high-quality research papers that advance the state-of-the-art in digital fabrication. Topics related to computer graphics, geometry processing, mechanical engineering, material science, architecture, human-computer interaction, robotics, and applied math are all welcome.

Please note that authors of papers accepted to the 2017 ACM Symposium on Computational Fabrication are invited to submit significantly revised versions of their manuscripts (>30% new content) to this Special Section.

*Important Dates*
Submission deadline: Feb 1, 2017
First Decision: March 1, 2018
Revision Submission: June 1, 2018
Online Publication: August 1, 2018

For further information and to access the submission system, please visit:

Best regards,
Stelian Coros and Stefanie Muller,
Guest Editors

QCDVis: a tool for the visualisation of Quantum Chromodynamics (QCD) data

Publication date: October 2017
Source:Computers & Graphics, Volume 67
Author(s): Dean P. Thomas, Rita Borgo, Robert S. Laramee, Simon J. Hands
Quantum Chromodynamics, most commonly referred to as QCD, is a relativistic quantum field theory for the strong interaction between subatomic particles called quarks and gluons. The most systematic way of calculating the strong interactions of QCD is a computational approach known as lattice gauge theory or lattice QCD. Space-time is discretised so that field variables are formulated on the sites and links of a four dimensional hypercubic lattice. This technique enables the gluon field to be represented using 3 × 3 complex matrices in four space-time dimensions. Importance sampling techniques can then be exploited to calculate physics observables as functions of the fields, averaged over a statistically-generated and suitably weighted ensemble of field configurations. In this paper we present a framework developed to visually assist scientists in the analysis of multidimensional properties and emerging phenomena within QCD ensemble simulations. Core to the framework is the use of topology-driven visualisation techniques which enable the user to segment the data into unique objects, calculate properties of individual objects present on the lattice, and validate features detected using statistical measures. The framework enables holistic analysis to validate existing hypothesis against novel visual cues with the intent of supporting and steering scientists in the analysis and decision making process. Use of the framework has lead to new studies into the effect that variation of thermodynamic control parameters has on the topological structure of lattice fields.

Full article: QCDVis: a tool for the visualisation of Quantum Chromodynamics (QCD) data

Comparison techniques utilized in spatial 3D and 4D data visualizations: A survey and future directions

Publication date: October 2017
Source:Computers & Graphics, Volume 67
Author(s): Kyungyoon Kim, John V. Carlis, Daniel F. Keefe
A variety of visualization techniques can be utilized to compare multiple Spatial 3D or time-varying Spatial 3D data instances (e.g., comparing pre- versus post-treatment volumetric medical images). However, despite the fact that comparative visualization is frequently needed – scientists, engineers, and even humanists must routinely compare such data – visualization users and practitioners suffer from a lack of adequate Spatial 3D comparative visualization tools and guidelines. Here we survey the field and present a taxonomy for classifying existing and new comparison visualization techniques for such data into four fundamental approaches: Juxtaposition, Superimposition, Interchangeable, and Explicit Encoding. The results clarify the key design decisions and tradeoffs that designers must make to create an effective comparative Spatial 3D data visualization and suggest the potential of emerging hybrid approaches, ones creatively combining aspects of the four fundamental approaches.

Full article: Comparison techniques utilized in spatial 3D and 4D data visualizations: A survey and future directions

Reconstruction of underlying surfaces from scanned data using lines of curvature

Publication date: November 2017
Source:Computers & Graphics, Volume 68
Author(s): Shoichi Tsuchie
This study presents a new method for reconstructing an underlying surface from scanned data of styling design objects. Our approach is based on sweep-based modeling, in which a surface is generated by sweeping a specified section curve along a 3D spine curve. However, it is difficult to determine the spine curve directly from the scanned data. Therefore, we generated a surface such that the trajectory of a point on the section curve approaches the line of curvature with less torsion of the surface to be generated while transforming the section curve. Compared with conventional approaches, our method can act as a guiding principle for reconstructing underlying surfaces via reverse engineering. The results of our experiments demonstrate that high-quality surfaces can be generated from real-world scanned data.

Full article: Reconstruction of underlying surfaces from scanned data using lines of curvature

Real-time labeling of non-rigid motion capture marker sets

Publication date: December 2017
Source:Computers & Graphics, Volume 69
Author(s): Simon Alexanderson, Carol O’Sullivan, Jonas Beskow
Passive optical motion capture is one of the predominant technologies for capturing high fidelity human motion, and is a workhorse in a large number of areas such as bio-mechanics, film and video games. While most state-of-the-art systems can automatically identify and track markers on the larger parts of the human body, the markers attached to the fingers and face provide unique challenges and usually require extensive manual cleanup. In this work we present a robust online method for identification and tracking of passive motion capture markers attached to non-rigid structures. The method is especially suited for large capture volumes and sparse marker sets. Once trained, our system can automatically initialize and track the markers, and the subject may exit and enter the capture volume at will. By using multiple assignment hypotheses and soft decisions, it can robustly recover from a difficult situation with many simultaneous occlusions and false observations (ghost markers). In three experiments, we evaluate the method for labeling a variety of marker configurations for finger and facial capture. We also compare the results with two of the most widely used motion capture platforms: Motion Analysis Cortex and Vicon Blade. The results show that our method is better at attaining correct marker labels and is especially beneficial for real-time applications.

Full article: Real-time labeling of non-rigid motion capture marker sets

Uncertainty visualization for interactive assessment of stenotic regions in vascular structures

Publication date: Available online 28 October 2017
Source:Computers & Graphics
Author(s): Gordan Ristovski, Jose Matute, Thomas Wehrum, Andreas Harloff, Horst K. Hahn, Lars Linsen
Stenosis refers to the thinning of the inner surface (lumen) of vascular structures. Detecting stenoses and correctly estimating their degree is crucial in clinical settings for proper treatment planning. Such a planning involves a visual assessment, which in case of vascular structures is frequently based on 3D visual representations of the vessels. However, since vessel segmentation is affected by various sources of errors and noise in the imaging and image processing pipeline, it is crucial to capture and visually convey the uncertainty in a 3D visual representation. Moreover, it is crucial to quantify how much this uncertainty affects the calculated stenotic degree, since different severities lead to different treatments. We propose a novel approach for visualizing the shape deviation of different probability levels in vascular data, where the probability levels are computed from a probabilistic segmentation approach. Our non-obstructive visual encoding is based on rendering a single opaque surface representing a probability level of the cumulative distribution function around the vessels’ centerline. The surface rendering is enhanced with cumulative information about other levels. To do so, we traverse the probability space by applying an iterative projection method both inwards and outward until we reach surface variability within a given margin. We capture the shape variability between the different probability levels using the lengths of the projection lines, the change in angular directions, and the distortion of a parametrization. They are visually encoded using color and texture mapping. Furthermore, we allow for an interactive selection of a region of interest that automatically calculates the stenotic degree and how much the uncertainty affects the most likely result. We analyze our approach in comparison to state-of-the-art methods with medical experts in a study using both real magnetic resonance (MR) and computed tomography (CT) angiography data of vertebral arteries with stenoses as well as on MR angiography data with synthetically added stenoses and stenotic uncertainties. We evaluate how well our approach can guide medical experts in their assessment of the uncertainty in vertebral stenoses.

Full article: Uncertainty visualization for interactive assessment of stenotic regions in vascular structures

Adjusting stereoscopic parameters by evaluating the point of regard in a virtual environment

Publication date: December 2017
Source:Computers & Graphics, Volume 69
Author(s): Jessica Conti, Benoît Ozell, Eric Paquette, Patrice Renaud
Despite the growth in research and development in the area of virtual reality over the past few years, virtual worlds do not yet convey a feeling of presence that matches reality. This is particularly due to the difference in visual perception of flat images as compared to actual 3D. We studied the impact of two parameters of the stereoscopic configuration, namely, the inter-camera distance (ICD) and the presence of a depth of field blur (DOF blur). We conducted an experiment involving 18 participants in order to evaluate this impact, based on both subjective and objective criteria. We examined six configurations which differed in the presence or absence of DOF blur and the value of the ICD: fixed and equal to the anatomical interpupillary distance, fixed and chosen by the participant, or variable, depending on the depth of the viewer’s point of regard (POR). The DOF blur and the variable ICD require the use of an eye tracking system in order to be adjusted with respect to the POR. To our knowledge, no previously published research has tested a gaze-contingent variable ICD along with dynamic DOF blur in a Cave Automatic Virtual Environment. Our results show that the anatomical and variable ICD performed similarly regarding each criterion of the experiment, both being more efficient than the fixed ICD. Besides, as with earlier similar attempts, the configurations with DOF blur obtained lower subjective evaluations. Although mainly not significant, the results obtained by the variable ICD and DOF blur are likely due to a noticeable delay in the parameters update. We also designed a new methodology to objectively compare the geometry and depth rendering, based on the reproduction of the same scene in the real and virtual setups, and then on the study of resulting ocular convergence and angular deviation from a target. This leads to a new comparative criterion for the perceptual realism of immersive virtual environments based on the visual behavior similarity between real and virtual setups.

Full article: Adjusting stereoscopic parameters by evaluating the point of regard in a virtual environment

A line-feature label placement algorithm for interactive 3D map

Publication date: October 2017
Source:Computers & Graphics, Volume 67
Author(s): Jiangfeng She, Jianlong Liu, Chuang Li, Jiaqi Li, Qiujun Wei
In an interactive three-dimensional (3D) map, the relief of the terrain can obstruct annotations. As the perspective moves and rotates freely in 3D space, the occlusion relationship among annotations changes accordingly. The direction of a line in general definitively influences the orientations of the characters in its annotation label, which affects its readability. Furthermore, a line that extends deep into 3D space requires annotation-reference line segments at different scales because the distant parts of a line appear less detailed than closer ones, and the positioning of the text of its annotation should be adjusted accordingly. In this paper, a rule set for 3D interactive map line-feature annotations is proposed and a screen-based line-feature annotation-placement algorithm is implemented. The purpose of our algorithm is to ensure that the annotations are readable from multiple angles, not obstructed by other annotations, terrains, or artificial structures, convey the directions of the lines, and conform to the traditional positioning preferences in cartography.

Full article: A line-feature label placement algorithm for interactive 3D map

Position based simulation of solids with accurate contact handling

Publication date: December 2017
Source:Computers & Graphics, Volume 69
Author(s): Mihai Frâncu, Florica Moldoveanu
Simulating multi-body dynamics with both rigid and flexible parts and with frictional contacts is a hard problem. We solve this by expressing the couplings between the bodies as position level constraints. The implicit treatment of the constraint directions gives us improved stability over velocity based methods. Then by employing regularization of nonlinear constraints and a convex minimization formulation, we bridge constraint-based methods to traditional force-based methods. In fact, the former are just a dual variables formulation of the latter. We solve this dual problem using position based dynamics (PBD). We show how PBD is a completely valid modeling technique and we extend it with an accurate contact and Coulomb friction model. We further show for the first time how the same solver can be used to simulate both rigid and deformable solids with two way coupling. For the soft bodies we introduce a novel form of linear finite elements expressed as constraints, that is more accurate than PBD mass-spring systems. More of our results include the energy conserving Newmark integrator and the accelerated Jacobi solver suitable for parallel architectures. Note that this paper is an extended and revised version of the conference paper published in [1].

Full article: Position based simulation of solids with accurate contact handling

Detection of hierarchical intrinsic symmetry structure in 3D models

Publication date: Available online 8 August 2017
Source:Computers & Graphics
Author(s): Hui Liu, Jiazhi Xia, Jianer Chen, Jianxin Wang
The structure of a 3D model is essential for identifying and understanding of the object. A large number of models show hierarchical structures, which are not only efficient for shape characterization, but also applicable to structural/topological editing. However, how to construct the hierarchical structure is challenging. Most of the existing methods construct the hierarchical structure of a model based on the local relationships among parts. We propose Hierarchical Intrinsic Symmetry Structure (HISS) to represent the structure of models and an automatic construction approach. The analysis of intrinsic symmetry is based on the skeleton of the model. First, we extract skeletons of semantic parts of a model and construct skeleton graph. Next, we calculate the similarities among parts. Then, we employ a voting strategy to determine the hierarchical structure centers according to the intrinsic symmetry among similar part pairs. Finally, we construct the HISS based on the skeleton graph and the detected hierarchical centers. We evaluate the representation and the algorithm with a set of experiments and applications, including model set analysis, model repairing and model synthesis.

Full article: Detection of hierarchical intrinsic symmetry structure in 3D models