Solid reconstruction using recognition of quadric surfaces from orthographic views

International audienceThe reconstruction of 3D objects from 2D orthographic views is crucial for maintaining and further developing existing product designs. A B-rep oriented method for reconstructing curved objects from three orthographic views is presented by employing a hybrid wire-frame in place of an intermediate wire-frame. The Link-Relation Graph (LRG) is introduced as a multi-graph representation of orthographic views, and quadric surface features (QSFs) are defined by special basic patterns of LRG as well as aggregation rules. By hint-based pattern matching in the LRGs of three orthographic views in an order of priority, the corresponding QSFs are recognized, and the geometry and topology of quadric surfaces are recovered simultaneously. This method can handle objects with interacting quadric surfaces and avoids the combinatorial search for tracing all the quadric surfaces in an intermediate wire-frame by the existing methods. Several examples are provided

A framework for hull form reverse engineering and geometry integration into numerical simulations

The thesis presents a ship hull form specific reverse engineering and CAD integration framework. The reverse engineering part proposes three alternative suitable reconstruction approaches namely curves network, direct surface fitting, and triangulated surface reconstruction. The CAD integration part includes surface healing, region identification, and domain preparation strategies which used to adapt the CAD model to downstream application requirements. In general, the developed framework bridges a point cloud and a CAD model obtained from IGES and STL file into downstream applications

Appearance Preserving Rendering of Out-of-Core Polygon and NURBS Models

In Computer Aided Design (CAD) trimmed NURBS surfaces are widely used due to their flexibility. For rendering and simulation however, piecewise linear representations of these objects are required. A relatively new field in CAD is the analysis of long-term strain tests. After such a test the object is scanned with a 3d laser scanner for further processing on a PC. In all these areas of CAD the number of primitives as well as their complexity has grown constantly in the recent years. This growth is exceeding the increase of processor speed and memory size by far and posing the need for fast out-of-core algorithms. This thesis describes a processing pipeline from the input data in the form of triangular or trimmed NURBS models until the interactive rendering of these models at high visual quality. After discussing the motivation for this work and introducing basic concepts on complex polygon and NURBS models, the second part of this thesis starts with a review of existing simplification and tessellation algorithms. Additionally, an improved stitching algorithm to generate a consistent model after tessellation of a trimmed NURBS model is presented. Since surfaces need to be modified interactively during the design phase, a novel trimmed NURBS rendering algorithm is presented. This algorithm removes the bottleneck of generating and transmitting a new tessellation to the graphics card after each modification of a surface by evaluating and trimming the surface on the GPU. To achieve high visual quality, the appearance of a surface can be preserved using texture mapping. Therefore, a texture mapping algorithm for trimmed NURBS surfaces is presented. To reduce the memory requirements for the textures, the algorithm is modified to generate compressed normal maps to preserve the shading of the original surface. Since texturing is only possible, when a parametric mapping of the surface - requiring additional memory - is available, a new simplification and tessellation error measure is introduced that preserves the appearance of the original surface by controlling the deviation of normal vectors. The preservation of normals and possibly other surface attributes allows interactive visualization for quality control applications (e.g. isophotes and reflection lines). In the last part out-of-core techniques for processing and rendering of gigabyte-sized polygonal and trimmed NURBS models are presented. Then the modifications necessary to support streaming of simplified geometry from a central server are discussed and finally and LOD selection algorithm to support interactive rendering of hard and soft shadows is described

Towards Predictive Rendering in Virtual Reality

The strive for generating predictive images, i.e., images representing radiometrically correct renditions of reality, has been a longstanding problem in computer graphics. The exactness of such images is extremely important for Virtual Reality applications like Virtual Prototyping, where users need to make decisions impacting large investments based on the simulated images. Unfortunately, generation of predictive imagery is still an unsolved problem due to manifold reasons, especially if real-time restrictions apply. First, existing scenes used for rendering are not modeled accurately enough to create predictive images. Second, even with huge computational efforts existing rendering algorithms are not able to produce radiometrically correct images. Third, current display devices need to convert rendered images into some low-dimensional color space, which prohibits display of radiometrically correct images. Overcoming these limitations is the focus of current state-of-the-art research. This thesis also contributes to this task. First, it briefly introduces the necessary background and identifies the steps required for real-time predictive image generation. Then, existing techniques targeting these steps are presented and their limitations are pointed out. To solve some of the remaining problems, novel techniques are proposed. They cover various steps in the predictive image generation process, ranging from accurate scene modeling over efficient data representation to high-quality, real-time rendering. A special focus of this thesis lays on real-time generation of predictive images using bidirectional texture functions (BTFs), i.e., very accurate representations for spatially varying surface materials. The techniques proposed by this thesis enable efficient handling of BTFs by compressing the huge amount of data contained in this material representation, applying them to geometric surfaces using texture and BTF synthesis techniques, and rendering BTF covered objects in real-time. Further approaches proposed in this thesis target inclusion of real-time global illumination effects or more efficient rendering using novel level-of-detail representations for geometric objects. Finally, this thesis assesses the rendering quality achievable with BTF materials, indicating a significant increase in realism but also confirming the remainder of problems to be solved to achieve truly predictive image generation

High-Quality Simplification and Repair of Polygonal Models

Because of the rapid evolution of 3D acquisition and modelling methods, highly complex and detailed polygonal models with constantly increasing polygon count are used as three-dimensional geometric representations of objects in computer graphics and engineering applications. The fact that this particular representation is arguably the most widespread one is due to its simplicity, flexibility and rendering support by 3D graphics hardware. Polygonal models are used for rendering of objects in a broad range of disciplines like medical imaging, scientific visualization, computer aided design, film industry, etc. The handling of huge scenes composed of these high-resolution models rapidly approaches the computational capabilities of any graphics accelerator. In order to be able to cope with the complexity and to build level-of-detail representations, concentrated efforts were dedicated in the recent years to the development of new mesh simplification methods that produce high-quality approximations of complex models by reducing the number of polygons used in the surface while keeping the overall shape, volume and boundaries preserved as much as possible. Many well-established methods and applications require "well-behaved" models as input. Degenerate or incorectly oriented faces, T-joints, cracks and holes are just a few of the possible degenaracies that are often disallowed by various algorithms. Unfortunately, it is all too common to find polygonal models that contain, due to incorrect modelling or acquisition, such artefacts. Applications that may require "clean" models include finite element analysis, surface smoothing, model simplification, stereo lithography. Mesh repair is the task of removing artefacts from a polygonal model in order to produce an output model that is suitable for further processing by methods and applications that have certain quality requirements on their input. This thesis introduces a set of new algorithms that address several particular aspects of mesh repair and mesh simplification. One of the two mesh repair methods is dealing with the inconsistency of normal orientation, while another one, removes the inconsistency of vertex connectivity. Of the three mesh simplification approaches presented here, the first one attempts to simplify polygonal models with the highest possible quality, the second, applies the developed technique to out-of-core simplification, and the third, prevents self-intersections of the model surface that can occur during mesh simplification

Funktionelle Herzklappen-Stent Designs für zukünftige autologe, transkatheter Klappenprothesen in pulmonaler Position

Background Transcatheter pulmonary valve replacement (TPVR) has asserted its position as a cornerstone in cardiology and become a nonsurgical alternative for patients with a dysfunctional right ventricular outflow tract (RVOT), demonstrating excellent early and late clinical outcomes. Short- and long-term complications of TPVR include stent fracture and migration, coronary compression, and valve regurgitation. Objective The purpose of this study is to describe methodology for developing Nitinol stents by conducting a computational design and finite element analysis in conjunction with 3D reconstruction of animal cardiac CT for TPVR. Methods 3D cardiac CT reconstruction was achieved using 3D Slicer, from which the RVOT + pulmonary artery (PA) was exported for blood flow simulation and hoop force acquisition with the stents. Functional stents were designed using Autodesk Fusion 360 and divided into three morphological geometries: group 1–straight tubular stents, group 2–corollaceous stents, and group 3–corollaceous stents with an elliptic geometry. Stent simulations for stent life and radial force, and the hoop force of the stent during expansion with the RVOT+PA model were obtained in Ansys. The blood flow simulation of RVOT+PA was performed using Ansys with the velocity-based coupled solver. Results 3D cardiac CT reconstructions were obtained in STL format, from which the right ventricle (RV) +PA model was performed for the blood flow simulation and the hoop force was obtained with the stents. Twelve functional stents were successfully designed and exported in SAT and STP formats for simulation. All stent life (Times)/radial force (N) were achieved: Group 1 comprised the stents DGS 3 (3219.2/1.88E+05), DGS 5 (16406/1.94E+05), DGS 7 (1.00E+06/1.89E+05), DGS 8B (0/3.74E+05), DGS-10B (8370.1/2.41E+05), DGS 12D (1.00E+06/2.41E+08); Group 2 comprised the stents DGS 8A (0/3.60E+05), DGS 9A (0/3.60E+05), DGS 10A (46093/2.28E+05), DGS 12C (2.50E+005/1.69E+05); Group 3 comprised the stents DGS 12A (1.00E+06/2.38E+08), DGS 12B (54509/2.20E+05). Hoop force (N) was obtained from the 12 stents: Group 1–DGS 5 (57802), DGS 7 (54647), DGS 8B (53248), DGS 10B (56650), DGS 12D (46297). Group 2–DGS 8A (50490), DGS 9A (60393), DGS 10A (23639), DGS 12C (29802). Group 3–DGS 12A (16368), DGS 12B (16368). The RV+PA blood flow simulation demonstrated that the anterior part of the PA wall had the largest shear force. Conclusions DGS 12C, DGS 12D, DGS 10A, DGS 10B, DGS 7, and DGS 5 can be subsequently tested in vitro. Autologous pulmonary valves could be sutured onto the functional stents to maintain their original geometry prior to implantation. Pre-implantation 3D CT reconstruction and stent simulation can be performed for better evaluation and visualization. The RV+PA blood flow simulation may serve as a significant input for the design of stents and pulmonary valve to determine the shear force throughout the cardiac cycle.Hintergrund Der katheterbasierte Pulmonalklappenersatz ist ein Eckpfeiler der Kardiologie und bietet zudem eine nicht-chirurgische Alternative für die Behandlung funktionsgestörter rechtsventrikulärer Ausflusstrakte oder bioprothetischer Klappen mit hervorragenden frühen und späten klinischen Ergebnissen. Kurz- und langfristige Komplikationen von TPVR umfassen Stentfraktur/-migration, Komprimierung der Koronararterien und Klappeninsuffizienz. Ziel Ziel dieser Studie ist es, die Methodik und das Konzept für Nitinol-Stents mithilfe rechnerischer Entwürfe und Finite-Elemente-Analysen anhand von 3D-Rekonstruktionen kardialer CT-Untersuchungen in Tieren für die Anwendung von TPVR zu beschreiben. Methoden Die 3D-Rekonstruktion der CT-Untersuchungen erfolgte mit der Software 3D Slicer, aus der die RVOT und Pulmonalarterie (PA) in Verbindung mit den Stents für die Blutflusssimulation und die Umfangsspannung exportiert wurde. Die funktionellen Stents wurden mit Fusion 360 entworfen und danach in die Formate SAT und STP exportiert. Simulationen für die Lebensdauer und Radialkraft sowie für die Umfangsspannung der Stents bei der Freisetzung mit dem RVOT+PA-Modell wurden in Ansys berechnet. Die Blutflusssimulation von RVOT+PA wurde in Ansys mit dem geschwindigkeitsbasierten gekoppelten Solver durchgeführt. Ergebnisse Zwölf funktionelle Stents wurden mithilfe von Fusion 360 generiert. SAT- und STP-Dateien wurden zur Simulation in Ansys exportiert. 3D Kardio-CT-Rekonstruktionen wurden mithilfe im STL-Format kreiert, aus dem das RVOT+PA-Modell des Prä-CT ausgewählt wurde, um die Blutflusssimulation durchzuführen und die Ringkraft der Stents zu erhalten. Die Lebensdauer (Anzahl) und Radialkraft (N) der Stents wurden wie folgt berechnet: DGS-3 (3219.2/1.88E+05), DGS-5 (16406/1.94E+05), DGS-7 (1.00E+06/1.89E+05), DGS-8A (0/3.60E+05), DGS-8B (0/3.74E+05), DGS-9A (0/3.60E+05), DGS-10A (46093/2.28E+05), DGS-10B (8370.1/2.41E+05), DGS-12A (1.00E+06/2.38E+08), DGS-12B (54509/2.20E+05), DGS-12D (1.00E+06/2.41E+08), DGS-12C (2.50E+005/1.69E+05). Die jeweilige Umspannungskraft (N) wurde wie folgt berechnet: DGS-5 (57802), DGS-7 (54647), DGS-8A (50490), DGS-8B (53248), DGS-9A (60393), DGS-10A (23639), DGS-10B (56650), DGS-12A (16368), DGS-12B (16368), DGS-12C (29802), DGS-12D (46297). Die RV+PA-Blutflusssimulation zeigte, dass der vordere Teil der PA-Wand die größte Scherkraft aufwies. Schlussfolgerungen DGS-12C, DGS-12D, DGS-10A, DGS-10B, DGS-7 und DGS-5 können nachfolgend in vitro getestet werden. Autologe Pulmonalklappen können zur Erhaltung der ursprünglichen Geometrie vor der Implantation auf funktionelle Stents aufgenäht werden. Vor der Implantation können Kardio-CT 3D-Rekonstruktion und Stentsimulationen zur besseren Bewertung und Visualisierung durchgeführt werden. Die Blutflusssimulation von RVOT+PA kann einen bedeutsamen Beitrag zur Gestaltung von Stents und Pulmonalklappen leisten, um die Scherkraft während des gesamten Herzzyklus zu erhalten

Feature-based Product Modelling in a Collaborative Environment

Ph.DDOCTOR OF PHILOSOPH

Automatic Mesh Repair and Optimization for Quality Mesh Generation

Ph.DDOCTOR OF PHILOSOPH