Category Archives: Archive

CG Colloquium Thursday May 16th

You are cordially invited to attend our CG Colloquium on Thursday, May 16, 2019, 15:45-17:45h, at Pulse-Technology.

The program features the following two speakers:

Gijs Reichert

Title: Improving video analysis for the Olympic dinghy class sailing coaches and athletes

Abstract: Nowadays technology and data analytics are becoming increasingly intertwined with sports. The data can help assess performance during training and in competitive settings. However, for most sailors in the Olympic dinghy class it holds that the use of sensors during training is not standard practice and not allowed during races. To record and review their performance the coaches and athletes make use of video, shot (often by holding a camera in hand) from the a coach boat. The goal is to improve the capture, processing and analysis of videos used to train sailing athletes in the dinghy class. More specifically, the stabilization and quality of the footage taken from the coach boat that follows athletes will be improved. Next to this, of the entire recorded session only the interesting parts for the coach and athletes will be highlighted and extracted. To achieve this segmentation into clips object tracking will be used as well as methods to detect sailing manoeuvres. From these video clips the heel angle, position in boat and rudder movements can be extracted or enhanced to support the coaches in their assessment. The proposed approach should lead to a time-saving method to extract more information from the videos previously possible to support the training of the dutch Olympic sailing team.

Levi van Aanholt

Title: Semantic Tile Solving for Procedural Generation of Architectural Spaces

Abstract: We present an offline tile solving technique to generate complex architectural spaces. The generation is controlled by the notion of an architectural profile. An architectural profile allows to declaritively control spatial creation. It consists of semantic tiles representing building elements and declarative rules to control the generation according to architectural relations. This problem is converted to an ASP logic program and subsequently solved by an ASP solver. Our technique results in a declarative architecture generator that unifies procedurally generating building exterior, building interior and traversal in one system.

CG Colloquium Thursday May 2nd

You are cordially invited to attend our CG Colloquium on Thursday, May 2nd, 2019, 15:45-17:45h, at Pulse Hall 4

The program features the following three speakers:

Huinan Jiang

Title: Player model analysis for adaptive content delivery in an educational game

Abstract: Player in games has been a useful way for understanding player motivation, style and preferences, assisting us to predict their behaviour, adapt the and improve user experience. For serious games, learning is also an factor to consider. Most work done in this area is about adaptive difficulty. While in our educational game Squla, students are exposed to multiple game types, it’s interesting to know how their behavioural data could their game type preference, and whether custom game type delivery could improve students’ engagement and learning. Therefore we present a player analysis method game adaptation, and experiment with target student groups to look into the impact.

Antony Löbker

Title: Automatic reconstruction of real-world buildings using open data

Abstract: Using publicly available data , such as Google streetview panoramas and OpenStreetMap building, it is possible to reconstruct real-world buildings. While these are not highly detailed, they will give a general impression of a. The proposed method can quickly reconstruction an entire neighbourhood in major urban centers around the world.

Julie Hongping Feng

Title: Building a 4D MRI blood flow statistical model

Abstract: Cardiovascular (CVDs) are the global number one cause of death. Current of CVDs is mainly based on functions and morphology of cardiovascular, and 4D MRI blood flow data has become a new and powerful source of, which allows both anatomical and functional analysis in a single. However, it is still difficult to efficiently utilize this data source diagnose CVDs. One of the main reasons is the lack of standard analysis and understanding of this rather new imaging modality. The method to understand the healthy behaviour and its variation is to build an atlas. Current blood flow atlas do not support 3D velocity vector field full information. We attempt to build a 4D MRI blood flow atlas similar to statistical shape and appearance models by applying Principal Component Analysis (PCA) to get the mean and main variations of the blood flow fields. The of this atlas would help physicians understand the 4D MRI data and assist them to identify whether the data is abnormal or not. In order to more efficient representations of variations for vector fields, we also tested Complex PCA and Quaternion PCA, besides traditional Real PCA. Finally, will visualize the results such that they can be interpretable.

CG Colloquium Thursday April 18th

You are cordially invited to attend our CG Colloquium on Thursday, April 18, 2019,
15:45-17:45h, at Pulse Hall 4 .

The program features the following three speakers:

Remi van der Laan

Title: Enhancing Compression of the Sparse Voxel Directed Acyclic Graph

Abstract: Rendering massive scenes in real time represented as voxels has emerged as an attractive alternative compared to the traditional rendering pipeline. This has been achieved through the development of data structures that can efficiently store the scene data while also being inexpensive to traverse. The Sparse Voxel Directed Acyclic Graph is such a data structure, which losslessly compresses geometry by exploiting the spatial coherence in the scene. We attempt enhance the effectiveness of this compression through modifications to the construction of the graph and investigate possibility of applying lossy compression techniques.

Hao Ming Ye

Title: not available at the moment

Abstract: not available at the moment

Ruben Wiersma

Title: Graph Convolutional Networks for Learning on Point Clouds

Abstract: In the past decade, Convolutional Neural Networks (CNNs) have achieved incredible results. A recent development in the deep learning community is the attempt to generalise the advantages of CNNs from a Euclidean domain to non-Euclidean domains, like graphs and manifolds. Some examples of graph data are social networks, regulatory networks, functional networks, and 3D shapes. We attempt to get an understanding of the methods currently available and aim to improve on the current methodology for learning on point clouds. A tentative conclusion is that the conceptually simple Graph Convolutional Network by Kipf and Welling could be improved for manifolds through the incorporation of the connection Laplacian from vector diffusion maps.

CG Colloquium Thursday April 4th

You are cordially invited to attend our Computer Graphics and Visualization Seminar on Thursday,
April 4, 2019, 15:45-17:45h, at Pulse Hall 7.

The program features the following three speakers:

Ruben VroegindeWeij (PRELIMINARY)
Title: Motion in Image
Abstract: We present a method to encode motion in a single image by mixing frames from different time origins with a simple user interface.

Mark van de Ruit
Title: Pre-Estimated Spectral Rendering
Abstract: Spectral Monte-Carlo rendering algorithms are suited for reproducing several advanced light phenomena such as dispersion and colored particle scattering. However, spectral rendering comes at the cost of increased (colored) image noise, as now additional samples are required in the spectral domain. We propose to iteratively build estimates of the spectral distributions in a scene during rendering, and use these estimates to guide sampling of the spectral domain. This method can lower variance from spectral sampling in specific situations, which is demonstrated with a working implementation in a conventional path tracer.

Felix Yang
Title: Adaptive Multi-view Ambient Occlusion
Abstract: Screen-space ambient occlusion and obscurance is a group of techniques that approximate the ambient occlusion or obscurance lighting model in the screen-space. They are ubiquitously adopted in modern video games, but suffer from view-dependent artifacts. One possible method to remedy such artifacts is using additional auxiliary cameras to aid the computation, but the improvement diminishes if the auxiliary cameras have poor coverage of the main scene. This project aims to develop techniques to adaptively manipulate the auxiliary cameras to ensure good coverages, therefore a more stable improvement over the single-view result.

Workshop Visual Analytics and Applications

You are all cordially invited to workshop visual analytics and applications, which will take place on 8th of April, from 14:00-17:00 at Pulse-hall 4. Please find detailed program below.

14:00 Jean Daniel Fekete: “Exploring the Evolution of Relationships with Dynamic Hypergraphs”

14:40 Renata Raidou: “Employing Visual Analytics for the Exploration and Prediction”

15:20 Break

15:30 Cagatay Turkay: “Informed computational modelling through visual analytics”

Abstract: With
the increasing availability of computational data analysis and modelling tools
that can be utilised out-of-the-box, the route from data to results is now much
shorter. However, these advancements also come together their own limitations,
and a data scientists need to be aware of the pitfalls and act carefully to
question every observation and method used within each step of the data
analysis process. Visual analytics approaches where interactive visualisations
are coupled tightly with the algorithms offer effective methodologies in
conducting data science in such inquisitive, rigorous ways. This talk will
discuss how visual analytics can facilitate such practices and will look at
examples of research on how data can be transformed and visualised creatively
in multiple perspectives, on how comparisons can be made within different
models, parameters, and within local and global solutions, and on how
interaction is an enabler for such processes.

16:10 Thomas Hollt: Cytosplore: Visual Analytics for Single-Cell Profiling of the Immune System
Recent advances in single-cell acquisition technology have led to a shift towards single-cell analysis in many fields of biology. In immunology, detailed knowledge of the cellular composition is of interest, as it can be the cause of deregulated immune responses, which cause diseases. Similarly, vaccination is based on triggering proper immune responses; however, many vaccines are ineffective or only work properly in a subset of those who are vaccinated. Identifying differences in the cellular composition of the immune system in such cases can lead to more precise treatment. Cytosplore is an integrated, interactive visual analysis framework for the exploration of large single-cell datasets. We have developed Cytosplore in close collaboration with immunology researchers and several partners use the software in their daily workflow. Cytosplore enables efficient data analysis and has led to several discoveries alongside high-impact publications.

16:50 end

Prof. Eisemann to Receive 2019 Dutch Prize for ICT Research

Professor Elmar Eisemann – credits Mark Prins

Professor Eisemann is to be awarded the 2019 Dutch prize for ICT research (Nederlandse Prijs voor ICT-onderzoek). The well-deserved award is a recognition for Prof. Eisemann’s research into the accurate, detailed depiction of visualizations using modern graphics hardware. The prize will be officially awarded to Prof. Eisemann during the ICT Open 2019 in Hilversum. Congratulations to Prof. Eisemann!

CG Colloquium Thursday March 7th

Computer Graphics and Visualization Seminar on Thursday, March 7, 2019, 15:45-17:45h, at EWI-Lecture hall Chip.

The program features the following two speakers:

Remi van der Laan

Title: Exploiting Coherence in Time-Varying Voxel Data

Abstract: We encode time-varying voxel data for efficient storage and streaming. We store the equivalent of a separate sparse voxel octree for each frame, but utilize both spatial and temporal coherence to reduce the amount of memory needed. We represent the time-varying voxel data in a single directed acyclic graph with one root per time step. In this graph, we avoid storing identical regions by keeping one unique instance and pointing to that from several parents. We further reduce the memory consumption of the graph by minimizing the number of bits per pointer and encoding the result into a dense bitstream.

Michiel van Spaendonck

Title: Spatiotemporal Variance-Guided Filtering: Real-Time Reconstruction for Path-Traced Global Illumination

Abstract: We introduce a reconstruction algorithm that generates a temporally stable sequence of images from one path-per-pixel global illumination. To handle such noisy input, we use temporal accumulation to increase the effective sample count and spatiotemporal luminance variance estimates to drive a hierarchical, image-space wavelet filter. This hierarchy allows us to distinguish between noise and detail at multiple scales using local luminance variance.

Physically based light transport is a long-standing goal for real-time computer graphics. While modern games use limited forms of ray tracing, physically based Monte Carlo global illumination does not meet their 30Hz minimal performance requirement. Looking ahead to fully dynamic real-time path tracing, we expect this to only be feasible using a small number of paths per pixel. As such, image reconstruction using low sample counts is key to bringing path tracing to real-time. When compared to prior interactive reconstruction filters, our work gives approximately 10x more temporally stable results, matches reference images 5-47% better (according to SSIM), and runs in just 10ms (+- 15%) on modern graphics hardware at 1920×1080 resolution.

CG Colloquium Thursday February 21st

You are cordially invited to attend our Computer Graphics and Visualization Seminar on Thursday, February 21, 2019, 15:45-17:45h, at EWI-Lecture hall Chip.

The program features the following two speakers:

Nouri Khalass
Title: Visualizing Stars and Emission Nebulae
Abstract: We describe the star and nebula visualization techniques used to create a 3D volumetric visualization of the Orion Nebula. The nebula’s ionization layer is modeled first as a surface model, derived from infrared and visible light observations. The model is imported into a volume scene graph-based volume visualization system to simulate the nebula’s emissive gases. Stars are rendered using Gaussian spots that are attenuated with distance.

Mark van de Ruit
Title: Real-Time Polygonal-Light Shading with Linearly Transformed Cosines
Abstract: In this paper, we show that applying a linear transformation—represented by a 3 x 3 matrix—to the direction vectors of a spherical distribution yields another spherical distribution, for which we derive a closed-form expression. With this idea, we can use any spherical distribution as a base shape to create a new family of spherical distributions with parametric roughness, elliptic anisotropy and skewness. If the original distribution has an analytic expression, normalization, integration over spherical polygons, and importance sampling, then these properties are inherited by the linearly transformed distributions.

By choosing a clamped cosine for the original distribution we obtain a family of distributions, which we call Linearly Transformed Cosines (LTCs), that provide a good approximation to physically based BRDFs and that can be analytically integrated over arbitrary spherical polygons. We show how to use these properties in a realtime polygonal-light shading application. Our technique is robust, fast, accurate and simple to implement.

CG Colloquium Thursday February 7th

You are cordially invited to attend our Computer Graphics and Visualization Seminar on Thursday, February 7, 2019, 15:45-17:45h, at EWI-Lecture hall Chip.

The program features the following two speakers:

Haoming Yeh
Title: Projective Dynamics: Fusing Constraint Projections for Fast Simulation
Abstract: We present a new method for implicit time integration of physical systems. Our approach builds a bridge between nodal Finite Element methods and Position Based Dynamics, leading to a simple, efficient, robust, yet accurate solver that supports many different types of constraints. We propose specially designed energy potentials that can be solved efficiently using an alternating optimization approach. Inspired by continuum mechanics, we derive a set of continuum based potentials that can be efficiently incorporated within our solver. We demonstrate the generality and robustness of our approach in many different applications ranging from the simulation of solids,
cloths, and shells, to example-based simulation. Comparisons to Newton-based and Position Based Dynamics solvers highlight the benefits of our formulation.

Matthijs Amesz
Title: Inverse Diffusion Curves using Shape Optimization
Abstract: The inverse diffusion curve problem focuses on automatic creation of diffusion curve images that resemble user provided color fields. This problem is challenging since the 1D curves have a
nonlinear and global impact on resulting color fields via a partial differential equation (PDE). We introduce a new approach complementary to previous methods by optimizing curve geometry.
In particular, we propose a novel iterative algorithm based on the theory of shape derivatives. The resulting diffusion curves are clean and well-shaped, and the final image closely approximates
the input. Our method provides a user-controlled parameter to regularize curve complexity, and generalizes to handle input color fields represented in

CG Colloquium Thursday January 10th

You are cordially invited to attend our Computer Graphics and Visualization Seminar on Thursday, January 10,
2019, 15:45-17:45h, at Pulse-Hall 4.

The program
features the following two speakers:

Anmol Hanagodimath


Optimizing BRDF Orientations for the Manipulation of Anisotropic Highlights


This paper introduces a system for the direct editing of highlights produced by anisotropic BRDFs, which we call anisotropic highlights. We first provide a comprehensive analysis of the link between the direction of anisotropy and the shape of highlight curves for arbitrary object surfaces. The gained insights provide the required ingredients to infer BRDF orientations from a prescribed highlight tangent field. This amounts to a non-linear optimization problem, which is solved at interactive framerates during manipulation. Taking inspiration from sculpting software, we provide tools that give the impression of manipulating highlight curves while actually modifying their tangents. Our solver produces desired highlight shapes for a host of lighting environments and anisotropic BRDFs

Shang Xiang


The Heat Method for Distance Computation


We introduce the heat method for solving the single- or multiple-source shortest path problem on both flat and curved domains. A key insight is that distance computation can be split into two stages: first find the direction along which distance is increasing, then compute the distance itself. The heat method is robust, efficient, and simple to implement since it is based on solving a pair of standard sparse linear systems. These systems can be factored once and subsequently solved in near-linear time, substantially reducing amortized cost. Real-world performance is an order of magnitude faster than state-of-the-art methods, while maintaining a comparable level of accuracy. The method can be applied in any dimension, and on any domain that admits a gradient and inner product—including regular grids, triangle meshes, and point clouds. Numerical evidence indicates that the method converges to the exact distance in the limit of refinement; we also explore smoothed approximations of distance suitable for applications where greater regularity is desired.