Free-form solid modeling using deformations

Ankara : The Department of Computer Engineering and Information Sciences and the Institute of Engineering and Science of Bilkent Univ. , 1989.Thesis (Master's) -- Bilkent University, 1989.Includes bibliographical references leaves 46-48.One of the most important problems of available solid modeling systems is that the range of shapes generated is limited. It is not easy to model objects with free-form surfaces in a conventional solid modeling system. Such objects can be defined arl^itrarily but then operations on them are not transparent and complications occur. A method for achieving free-form effect is to define regular objects or surfaces, then deform them. This keeps various properties of the model intact while achieving the required visuaJ appearance. This thesis explains a number of geometric modeling techniques with deformations applied to them in attempts to combine various approaches developed so far. Regular deformations, which include twisting, bending, and tapering, and free-form deformation technique are combined as a new deformation method. This eliminates some of the disadvantages peculiar to each method and utilizes the advantages of both.Güdükbay, UğurM.S

Physically-based animation of elastically deformable models

Ankara : Depatment of Computer Engineering and Information Science and Institute of Engineering and Science, Bilkent Univ., 1994.Thesis (Ph.D.) -- Bilkent University, 1994.Includes bibliographical references leaves66-71Although kinematic modeling methods are adequate for describing the shapes of static objects, they are insufficient when it comes to producing realistic animation. Physically-based modeling remedies this problem by including forces, masses, strain energies, and other physical quantities. The behavior of physicallybased models is governed by the laws of rigid and nonrigid dynamics expressed through a set of equations of motion. In this thesis, we describe a system for the animation of deformable models. A spring force formulation for animating deformable models is also presented. The animation system uses the physicallybased modeling methods and the approaches from elasticity theory for animating the models. Three different formulations, namely the primal, hrjhrid, and the spring force formulations, are implemented so that the user could select the suitable one for an animation, considering the advantages and disadvantages of each formulation. Collision of the models with impenetrable obstacles and constraining model points to fixed positions iii space are implemented.Güdükbay, UğurPh.D

A hybrid representation for modeling, interactive editing, and real-time visualization of terrains with volumetric features

<div><p>Terrain rendering is a crucial part of many real-time applications. The easiest way to process and visualize terrain data in real time is to constrain the terrain model in several ways. This decreases the amount of data to be processed and the amount of processing power needed, but at the cost of expressivity and the ability to create complex terrains. The most popular terrain representation is a regular 2D grid, where the vertices are displaced in a third dimension by a displacement map, called a heightmap. This is the simplest way to represent terrain, and although it allows fast processing, it cannot model terrains with volumetric features. Volumetric approaches sample the 3D space by subdividing it into a 3D grid and represent the terrain as occupied voxels. They can represent volumetric features but they require computationally intensive algorithms for rendering, and their memory requirements are high. We propose a novel representation that combines the voxel and heightmap approaches, and is expressive enough to allow creating terrains with caves, overhangs, cliffs, and arches, and efficient enough to allow terrain editing, deformations, and rendering in real time.</p></div

Increasing the Sense of Presence in a Simulation Environment Using Image Generators Based on Visual Attention

Flight simulator systems generally use a separate image-generator component. The host is responsible for the positional data updates of the entities and the image generator is responsible for the rendering process. In such systems, the sense of presence is decreased by model flickering. This study presents a method by which the host can minimize model flickering in the image-generator output. The method is based on preexisting algorithms, such as visibility culling and level of detail management of 3D models. The flickering is minimized for the visually important entities at the expense of increasing the flickering of the entities that are out of the user's focus using a new perception-based approach. It is shown through user studies that the new proposed approach increases the participants' sense of presence