BSP-fields: An Exact Representation of Polygonal Objects by Differentiable Scalar Fields Based on Binary Space Partitioning

The problem considered in this work is to find a dimension independent algorithm for the generation of signed scalar fields exactly representing polygonal objects and satisfying the following requirements: the defining real function takes zero value exactly at the polygonal object boundary; no extra zero-value isosurfaces should be generated; C1 continuity of the function in the entire domain. The proposed algorithms are based on the binary space partitioning (BSP) of the object by the planes passing through the polygonal faces and are independent of the object genus, the number of disjoint components, and holes in the initial polygonal mesh. Several extensions to the basic algorithm are proposed to satisfy the selected optimization criteria. The generated BSP-fields allow for applying techniques of the function-based modeling to already existing legacy objects from CAD and computer animation areas, which is illustrated by several examples

Design of CT pictures from 2D to 3D

Volume visualization is one important part of scientific visualization. It has developed basing on absorbing the relative knowledge of computer delineation, computer visualization and computer image disposal. The knowledge of this branch is of much importance in computer application. Since it deals with contents with deeper meaning and it is more theoretic, having more arithmetic means, it generally stands for the level of computer application. The study and application of volume visualization is like a raging fire. My country started comparatively later in this field. This thesis gives systematic representation and discuss in the field of tomography image 3D reconstruction. It mainly discusses after rotation, translation, filtering, interpolation and sharpening a series of 2D CT scanning images, get the boundary data of different object to form 3D volume data and actualize the 3D reconstruction of the object, and at the same time implement the function of display, translation, rotation, scaling and projection the volume data. Basing on the implementation of these functions according to software programming, this thesis gives a sum up to each algorithm of 3D volume visualization processing. The method to actualize the 3D reconstruction of the tomography image is mainly about the image processing, image transformation, the way to actualize 3D reconstruction and image compression, etc. In image processing, it talks about getting the anchor points in the tomography image, the geometrie transformation of the image, getting the boundary of the target, cross section display and the smoothing and sharpening of the image. In the transformation of the image, this thesis deals with the algorithm and implementation principle of the geometric transformation (transition, rotation, and scaling) of the 2D image, the three-dimensionalization of the planar data, construction of the stereo mode, geometric transformation of the 3D graph, curve-fitting, the processing of hidden line and hidden surface, color processing. It also introduces the thoughts of using OpenGL to develop and actualize tomography image 3D reconstruction system, including using OpenGL to transform the coordinate, solid model building, to actualize 3D rotation and projection. Recently, the methods of applying chemotherapy to deal with cancer in hospitals of our country are different. Hospital with great fund takes import software to design while most of the hospitals take domestic software. These kinds of software are designed by DAHENG Company in BeiJing, WEIDA Company in ShenZhen. The programs in the software these two hospitals' doctors use to treat are images fielding in the plane not making radiation design under the mode of omnibearing cubic display. Under this circumstance the judgment of the key part can not remain precise, and this part is the most important part that the doctors need. The above problem is the aim of this project. This thesis mainly deals with the subject that after calibrating and sharpening the series of 2D CT images, extract the boundary data of different bodies to form a 3D volume data and actualize 3D reconstruction and at the same time actualize the function of display, translation, rotation, scaling and projection. Mostly basing on the application of medical area, this thesis aims at making further research on computer graphies, computer vision and computer image processing through the study and application of volume visualization in this field. By the study and development of the volume visualization technology in this project, it can provide simulation and display functions to the observer before the operation and the radiotherapy as well as providing the chance to simulate the real teaching and practicing link to the medical school in the teaching process, and increase the clinic level and teaching level of medical area.\ud ______________________________________________________________________________ \ud MOTS-CLÉS DE L’AUTEUR : volume visualization, volume data, tomography image, 3D reconstruction, anchor point, boundary data, periphery boundary, OpenGL

Procedural Historic Building Information Modelling (HBIM) For Recording and Documenting European Classical Architecture

Procedural Historic Building Information Modelling (HBIM) is a new approach for modelling historic buildings which develops full building information models from remotely sensed data. HBIM consists of a novel library of reusable parametric objects, based on historic architectural data and a system for mapping these library objects to survey data. Using concepts from procedural modelling, a new set of rules and algorithms have been developed to automatically combine HBIM library objects and generate different building arrangements by altering parameters. This is a semi-automatic process where the required building structure and objects are first automatically generated and then refined to match survey data. The encoding of architectural rules and proportions into procedural modelling rules helps to reduce the amount of further manual editing that is required. The ability to transfer survey data such as building footprints or cut-sections directly into a procedural modelling rule also greatly reduces the amount of further editing required. These capabilities of procedural modelling enable a more automated and efficient overall workflow for reconstructing BIM geometry from point cloud data. This document outlines the research carried out to evaluate the suitability of a procedural modelling approach for improving the process of reconstructing building geometry from point clouds. To test this hypothesis, three procedural modelling prototypes were designed and implemented for BIM software. Quantitative accuracy testing and qualitative end-user scenario testing methods were used to evaluate the research hypothesis. The results obtained indicate that procedural modelling has potential for achieving more accurate, automated and easier generation of BIM geometry from point clouds

Unstructured surface and volume decimation of tessellated domains

A general algorithm for decimating unstructured discretized data sets is presented. The discretized space may be a planar triangulation, a general 3D surface triangulation, or a 3D tetrahedrization. The decimation algorithm enforces Dirichlet boundary conditions, uses only existing vertices, and assumes manifold geometry. Local dynamic vertex removal is performed without history information while preserving the initial topology and boundary geometry. The tessellation at each step of the algorithm is preserved and, in the pathological case, every interior vertex is a candidate for removal. The research focuses on how to remove a vertex from an existing unstructured n-dimensional tessellation, not on the formulation of decimation criteria. Criteria for removing a candidate vertex may be based on geometric properties or any scalar governing function specific to the application. Use of scalar functions to adaptively control or optimize tessellation resolution is particularly applicable to the computer graphics, computational fluids, and structural analysis disciplines. Potential applications in the geologic exploration and medical or industrial imaging fields are promising

Automatic 3D Building Detection and Modeling from Airborne LiDAR Point Clouds

Urban reconstruction, with an emphasis on man-made structure modeling, is an active research area with broad impact on several potential applications. Urban reconstruction combines photogrammetry, remote sensing, computer vision, and computer graphics. Even though there is a huge volume of work that has been done, many problems still remain unsolved. Automation is one of the key focus areas in this research. In this work, a fast, completely automated method to create 3D watertight building models from airborne LiDAR (Light Detection and Ranging) point clouds is presented. The developed method analyzes the scene content and produces multi-layer rooftops, with complex rigorous boundaries and vertical walls, that connect rooftops to the ground. The graph cuts algorithm is used to separate vegetative elements from the rest of the scene content, which is based on the local analysis about the properties of the local implicit surface patch. The ground terrain and building rooftop footprints are then extracted, utilizing the developed strategy, a two-step hierarchical Euclidean clustering. The method presented here adopts a divide-and-conquer scheme. Once the building footprints are segmented from the terrain and vegetative areas, the whole scene is divided into individual pendent processing units which represent potential points on the rooftop. For each individual building region, significant features on the rooftop are further detected using a specifically designed region-growing algorithm with surface smoothness constraints. The principal orientation of each building rooftop feature is calculated using a minimum bounding box fitting technique, and is used to guide the refinement of shapes and boundaries of the rooftop parts. Boundaries for all of these features are refined for the purpose of producing strict description. Once the description of the rooftops is achieved, polygonal mesh models are generated by creating surface patches with outlines defined by detected vertices to produce triangulated mesh models. These triangulated mesh models are suitable for many applications, such as 3D mapping, urban planning and augmented reality