Takashi Ijiri

Floral diagrams and inflorescences: interactive flower modeling using botanical structural constraints

We present a system for modeling flowers in three dimensions quickly and easily while preserving correct botanical structures. We use floral diagrams and inflorescences, which were developed by botanists to concisely describe structural information of flowers. Floral diagrams represent the layout of floral components on a single flower, while inflorescences are arrangements of multiple flowers. Based on these notions, we created a simple user interface that is specially tailored to flower editing, while retaining a maximum variety of generable models. We also provide sketching interfaces to define the geometries of floral components. Separation of structural editing and editing of geometry makes the authoring process more flexible and efficient. We found that even novice users could easily design various flower models using our technique. Our system is an example of application-customized sketching, illustrating the potential power of a sketching interface that is carefully designed for a specific application.

The Sketch L-System: Global Control of Tree Modeling Using Free-Form Strokes

L-system is a tool commonly used for modeling and simulating the growth of plants. In this paper, we propose a new tree modeling system based on L-system that allows the user to control the overall appearance and the depth of recursion, which represents the level of growth, easily and directly, by drawing a single stroke. We introduce a new module into L-system whose growth direction is determined by a user-drawn stroke. As the user draws the stroke, the system gradually advances the growth simulation and creates a tree model along the stroke. Our technique is the first attempt to control the growth of a simulation in L-system using stroke input.

An Example-based Procedural System for Element Arrangement

We present a method for synthesizing two dimensional (2D) element arrangements from an example. The main idea is to combine texture synthesis techniques based‐on a local neighborhood comparison and procedural modeling systems based‐on local growth. Given a user‐specified reference pattern, our system analyzes neigh‐borhood information of each element by constructing connectivity. Our synthesis process starts with a single seed and progressively places elements one by one by searching a reference element which has local features that are the most similar to the target place of the synthesized pattern. To support creative design activities, we introduce three types of interaction for controlling global features of the resulting pattern, namely a spray tool, a flow field tool, and a boundary tool. We also introduce a global optimization process that helps to avoid local error concentrations. We illustrate the feasibility of our method by creating several types of 2D patterns.

Lapped solid textures: filling a model with anisotropic textures

We present a method for representing solid objects with spatially-varying oriented textures by repeatedly pasting solid texture exemplars. The underlying concept is to extend the 2D texture patch-pasting approach of lapped textures to 3D solids using a tetrahedral mesh and 3D texture patches. The system places texture patches according to the user-defined volumetric tensor fields over the mesh to represent oriented textures. We have also extended the original technique to handle nonhomogeneous textures for creating solid models whose textural patterns change gradually along the depth fields. We identify several texture types considering the amount of anisotropy and spatial variation and provide a tailored user interface for each. With our simple framework, large-scale realistic solid models can be created easily with little memory and computational cost. We demonstrate the effectiveness of our approach with several examples including trees, fruits, and vegetables.

Seamless Integration of Initial Sketching and Subsequent Detail Editing in Flower Modeling

We present an interactive modeling system for flower composition that supports seamless transformation from an initial sketch to a detailed three‐dimensional (3D) model. To begin, the user quickly sketches the overall appearance of the desired model as a collection of two‐dimensional (2D) strokes on hierarchical billboards. Then the user iteratively replaces the coarse sketch with a detailed 3D model referring to the initial sketch as a guide. Since a flower model consists of many repetitive components, the system helps the user to reuse 3D components to facilitate the modeling process. The global view of the entire model is always shown in a separate window to visualize how local modifications affect the global appearance. Our system helps the user make appropriate design decisions to keep the model consistent with the initial design, which is difficult in traditional bottom‐up plant modeling systems in which the global view only emerges after all of the details are specified.

A procedural method for modeling the purkinje fibers of the heart.

The Purkinje fibers are located in the ventricular walls of the heart, just beneath the endocardium and conduct excitation from the right and left bundle branches to the ventricular myocardium. Recently, anatomists succeeded in photographing the Purkinje fibers of a sheep, which clearly showed the mesh structure of the Purkinje fibers. In this study, we present a technique for modeling the mesh structure of Purkinje fibers semiautomatically using an extended L-system. The L-system is a formal grammar that defines the growth of a fractal structure by generating rules (or rewriting rules) and an initial structure. It was originally formulated to describe the growth of plant cells, and has subsequently been applied for various purposes in computer graphics such as modeling plants, buildings, streets, and ornaments. For our purpose, we extended the growth process of the L-system as follows: 1) each growing branch keeps away from existing branches as much as possible to create a uniform distribution, and 2) when branches collide, we connect the colliding branches to construct a closed mesh structure. We designed a generating rule based on observations of the photograph of Purkinje fibers and manually specified three terminal positions on a three-dimensional (3D) heart model: those of the right bundle branch, the anterior fascicle, and the left posterior fascicle of the left branch. Then, we grew fibers starting from each of the three positions based on the specified generating rule. We achieved to generate 3D models of Purkinje fibers of which physical appearances closely resembled the real photograph. The generation takes a few seconds. Variations of the Purkinje fibers could be constructed easily by modifying the generating rules and parameters.

Bilateral Hermite Radial Basis Functions for Contour-based Volume Segmentation

In this paper, we propose a novel contour‐based volume image segmentation technique. Our technique is based on an implicit surface reconstruction strategy, whereby a signed scalar field is generated from user‐specified contours. The key idea is to compute the scalar field in a joint spatial‐range domain (i.e., bilateral domain) and resample its values on an image manifold. We introduce a new formulation of Hermite radial basis function (HRBF) interpolation to obtain the scalar field in the bilateral domain. In contrast to previous implicit methods, bilateral HRBF (B‐HRBF) generates a segmentation boundary that passes through all contours, fits high‐contrast image edges if they exist, and has a smooth shape in blurred areas of images. We also propose an acceleration scheme for computing B‐HRBF to support a real‐time and intuitive segmentation interface. In our experiments, we achieved high‐quality segmentation results for regions of interest with high‐contrast edges and blurred boundaries.

Flower modeling via X-ray computed tomography

This paper presents a novel three dimensional (3D) flower modeling technique that utilizes an X-ray computed tomography (CT) system and real-world flowers. Although a CT system provides volume data that captures the internal structures of flowers, it is difficult to accurately segment them into regions of particular organs and model them as smooth surfaces because a flower consists of thin organs that contact one another. We thus introduce a semi-automatic modeling technique that is based on a new active contour model with energy functionals designed for flower CT. Our key idea is to approximate flower components by two important primitives, a shaft and a sheet. Based on our active contour model, we also provide novel user interfaces and a numerical scheme to fit these primitives so as to reconstruct realistic thin flower organs efficiently. To demonstrate the feasibility of our technique, we provide various flower models reconstructed from CT volumes.

Contour‐based Interface for Refining Volume Segmentation

Medical volume images contain ambiguous and low‐contrast boundaries around which existing fully‐ or semiautomatic segmentation algorithms often cause errors. In this paper, we propose a novel system for intuitively and efficiently refining medical volume segmentation by modifying multiple curved contours. Starting with segmentation data obtained using any existing algorithm, the user places a three‐dimensional curved cross‐section and contours of the foreground region by drawing a cut stroke, and then modifies the contours referring to the cross‐section. The modified contours are used as constraints for deforming a boundary surface that envelops the foreground region, and the region is updated by that deformed boundary. Our surface deformation algorithm seamlessly integrates detail‐preserving and curvature‐diffusing methods to keep important detail boundary features intact while obtaining smooth surfaces around unimportant boundary regions. Our system supports topological manipulations as well as contour shape modifications. We illustrate the feasibility of our system by providing examples of its application to the extraction of bones, muscles, kidneys with blood vessels, and bowels.

A Sketch-Based Interface for Modeling Myocardial Fiber Orientation that Considers the Layered Structure of the Ventricles

We propose a sketch-based interface for modeling the myocardial fiber orientation required in the electrophysiological simulation of the heart, especially the ventricles. The user can create a volumetric vector field that represents the myocardial fiber orientation in two steps. First, a depth field over the three-dimensional (3D) ventricular model is defined to create layers of myocardium. The user can then peel these layers and draw strokes on them to specify the myocardial fiber orientation in each layer. We represent the 3D ventricular model as a tetrahedral mesh and perform Laplacian smoothing over the mesh vertices to interpolate the vector field defined by the user-drawn strokes. Our method also allows the user to perform deformations on volumetric models of myocardial fiber orientation, which is very important for studying heart disease associated with morphological abnormalities. We created several examples of myocardial fiber orientation and applied them to a simplified simulator to demonstrate the effectiveness of our method.