Published papers

安価ながら効果的な裸眼立体表示を可能にするディスプレイシステムの開発は，ビジュアルコンピューティング分野におけるきわめて重要な課題の一つである．ホログラフィに代表されるような，ハードウェアの描像原理を高度化することで発展してきた既存システムは，現時点では生成映像の品質を向上させにくいという課題がある．そこで本論文では，複数枚の汎用ディスプレイを直交に配置したL 字型の表示空間上で，陰影と運動視差を中心とする単眼性の奥行 き知覚要因を利用して，一般的な2D グラフィックスと同等の解像度と明度をもつ，個人向けの裸眼立体映像を手軽に生成する手法を提案する．ユーザの視線追跡により本手法の有効性を確認する予備的評価についても報告する．

よく知られているように，方程式x^2+1=0は実数の範囲では解をもたない．そこで，関係式i^2+1= 0を満たすような虚数単位iを含むように数の次元を1つ上げて， a+ib の形の複素数を得たのであるが，たとえば交流回路のインピーダンス計算が複素数によって楽に行えることや，「虚数の光」ともよばれるエバネッセント（近接場）光が，マクスウェル方程式の平面波解（複素数で書かれる）として導かれることなど，「次元を上げると，こんなにいいことがある」例が数多く示されている．言い換えると，新しい理論やものの見方は，数理科学の視野を拡大するものでなければならないが，たとえそれらが合理的に有用なものとして受け入れられたとしても，そもそも2次元しか見えない3次元空間の住人が4次元以上の直積空間を理解しようとするのは容易なことではない．ここでは，4次元図形の直観像を得るための1つの方法として，複素初等関数の可視化と，その応用である「複素パラメータによる平面曲線の解析的な延長」について論じてみたい．

As a probability distribution on the high-dimensional sphere, the von Mises-Fisher (vMF) distribution is widely used for directional statistics and data analysis methods based on correlation. We considered a constrained vMF distribution for block modeling, which provides a probabilistic model of an asymmetric biclustering method that uses correlation as the similarity measure of data features. We derived the variational Bayesian inference algorithm for the mixture of the constrained vMF distributions. It was applied to a multivariate data visualization method implemented with enhanced parallel coordinate plots. This paper was presented at The International Meeting on High-Dimensional Data-Driven Science (HD3-2015), held in Kyoto in December 2015.

Type Ia supernovae (SNIa) have an almost uniform peak luminosity, so that they are used as "standard candle" to estimate distances to galaxies in cosmology. In this article, we introduced our two recent works on SNIa based on data-driven approach. The diversity in the peak luminosity of SNIa can be reduced by corrections in several variables. The color and decay rate have been used as the explanatory variables of the peak luminosity in past studies. However, it is proposed that their spectral data could give a better model of the peak luminosity. We use cross-validation in order to control the generalization error and a LASSO-type estimator in order to choose the set of variables. Using 78 samples and 276 candidates of variables, we confirmed that the peak luminosity depends on the color and decay rate. Our analysis does not support adding any other variables in order to have a better generalization error. On the other hand, this analysis is based on the assumption that SNIa originate in a single population, while it is not trivial. Indeed, several sub-types possibly having different nature have been proposed. We used a visual analytics tool for the asymmetric biclustering method to find both a good set of variables and samples at the same time. Using 14 variables and 132 samples, we found that SNIa can be divided into two categories by the expansion velocity of ejecta. Those examples demonstrate that the data-driven approach is useful for high-dimensional large-volume data which becomes common in modern astronomy. This paper was presented at The International Meeting on High-Dimensional Data-Driven Science (HD3-2015), held in Kyoto in December 2015.

Validation and exploration of the data generated by large-scale scientific simulations rely on sophisticated visualization and analysis tasks. With the advancement of supercomputing, the growing scale and complexity of the data make some of these tasks challenging, which demands new hardware and software solutions. We believe it is possible to address some of the challenges by utilizing the increasingly affordable see-through head mounted display (HMD) devices together with a low-cost tiled HDTV display. With the tiled display to provide a high-resolution overview of the data, the user can freely choose a small area to explore and analyze using a see-through HMD in stereoscopic 3D with gesture input. During such local exploration and detail data analysis, the user can apply a newly derived visualization parameter setting to the large tiled display for a new overview. In this way, computational costs become more manageable because realtime rendering and response are only required to cover a small screen space and a subset of the data. In our current study, we focus on supporting immersive isosurface and streamline visualization and analysis of 3D flow field data. In this workshop paper, we presented our preliminary design and results, and we also discussed our further development and evaluation plan.

本稿では, 即興演奏を行う楽器演奏者を対象ユーザとして, その演奏情報をリアルタイムに読み取り, それに呼応して映像生成を行うシステムを提案した. 提案システムでは, 演奏者の演奏をアフェクティブな評価基準をもって評価し, その結果に応じて映像生成を行い, 演奏者にインスピレーションを与えることを目指す. インスピレーションを得た演奏者が演奏を変化させ, またシステムはそれに呼応し映像を変化させるという, アフェクティブな表現のループを形成することで, 演奏者の「共演者」としての役割をシステムで再現することが, 本研究の目標である.

東北大学流体科学研究所で開発を進めてきた可視化設計ライフサイクル支援環境VIDELICET上でサポートするEFD/CFD融合可視化機能－並置化（juxtaposition）－について適用事例を用いて解説した． 本件は，第1回EFD/CFD融合研究会の招待講演資料である．

For exploring the inner structures of large scale volume datasets, it is general to use LoD control methods. In order to achieve effective large-scale volume visualization, we propose visualization guidelines to adaptively select appropriate Level of Detail (LoD) control methods according to the predetermined visualization techniques and the setting of parameter values. Our contribution lies in the automatic selection of LoD control methods for visualizing large-scale volume datasets so that even novices can effectively take advantage of the LoD control methods.

一般的に三次元コンピュータグラフィックスでは， 透視投影が用いられている．これに対し，人間が描く絵では， 複数の視点からの見えを混在させることにより， 表現したい対象の特徴を強調した非透視投影が用いられている． 本稿では， 二次元投影図上の見えを介して ユーザが非透視投影図のゆがみを編集することのできる新しい手法を提案する． この手法は， 三次元格子点上に定義されたカメラパラメータ場を データ構造として用いることにより， 一つの投影図に複数の視点を混在させることができるようにする． 更に，いくつかの基本操作を提供することで， ユーザが二次元投影面を介して，対象シーンを包含する カメラパラメータ場を編集できるようにする． 我々の手法を用いることで，三次元シーンの投影図を手描きの絵に合わせる いくつかの設計例を示す．

Parallel performance has been a challenging topic in streamline visualization for large unstructured flow datasets on parallel distributed-memory computers. It depends strongly on domain partitions. Unsuitable partitions often lead to severe load imbalance and high frequent communications among the domain partitions. To address the problem, we present an approach to flow data partitioning taking account of flow directions and features. Multilevel spectral graph bisection method is employed to reduce communication and synchronization overhead among distributed domains. Edge weights in the corresponding adjacent matrix is defined based on an anisotropic local diffusion operator which assigns strong coupling along flow direction and weak coupling orthogonal to flow. Meanwhile, the distributions of seed points and flow features such as vortex structure are also considered in partitioning so as to obtain good load balance. The experimental results are given to show the feasibility and effectiveness of our method.

The rapid advance in high performance computing and measurement technologies has recently made it possible to produce a stupendous amount of time-varying volume datasets in a variety of disciplines. However, there exist a few known visual exploration tools that allow us to investigate the core of their complex dynamics effectively. In this paper, our previous approach to topological volume skeletonization is extended to capture the topological features of large-scale time-varying volume datasets. A visual exploration tool, termed T-map, is presented, where pixel-oriented information visualization techniques are deployed so that the user can identify partial 4D spatiotemporal domains with characteristic changes in a topological sense, prior to detailed and comprehensible volume visualization. A case study with datasets from atomic collision research is performed to illustrate the feasibility of the proposed tool.

Locating optimal light sources is an important task for image synthesis because it significantly influences the spatial perception of rendered objects. Several methods have been proposed, which search for the optimal location of light sources for 3D surfaces, but none has been done for volumes. This paper presents a novel method for finding an optimal location of a single parallel light source for volumetric ray-casting. The method computes the entropy of brightness distribution of topologically-significant isosurfaces, and then utilizes a topologically-enhanced opacity transfer function to assign a distinct weight to each of the entropy values for the isosurfaces to evaluate the plausible illumination entropy for the entire volume. The light with the maximum entropy value facilitates the observers realizing the volume features with enriched 3D cues. Empirical evaluation of the present method with a simple analytic volume is also included.

本論文では，可視化目的から有効な可視化技法を特定する目的指向分類であるWehrendマトリックスを拡張した知識ベースを援用することによって，流れ場の可視化アプリケーション設計を支援し，既存のモジュール型可視化環境の利用を促進するシステムGADGET/FVを提案する．GADGET/FVは，ユーザの可視化スキルレベルに応じて支援内容を変化させる適応性だけでなく，作業過程の保存・再利用や，研究メモを可視化結果にリンクさせる機能をもつことによって，ユーザの視覚解析の進捗に合わせた，よりきめの細かい支援を実現している．流体解析の実例を用いて本システムの有効性を示すとともに，Robertsonらが提案する可視化システムの性能を定義する6つの要素にしたがって，本システムの性能を総合的に評価する．