Scalable Realtime Rendering and Interaction with Digital Surface Models of Landscapes and Cities

Interactive, realistic rendering of landscapes and cities differs substantially from classical terrain rendering. Due to the sheer size and detail of the data which need to be processed, realtime rendering (i.e. more than 25 images per second) is only feasible with level of detail (LOD) models. Even the design and implementation of efficient, automatic LOD generation is ambitious for such out-of-core datasets considering the large number of scales that are covered in a single view and the necessity to maintain screen-space accuracy for realistic representation. Moreover, users want to interact with the model based on semantic information which needs to be linked to the LOD model. In this thesis I present LOD schemes for the efficient rendering of 2.5d digital surface models (DSMs) and 3d point-clouds, a method for the automatic derivation of city models from raw DSMs, and an approach allowing semantic interaction with complex LOD models. The hierarchical LOD model for digital surface models is based on a quadtree of precomputed, simplified triangle mesh approximations. The rendering of the proposed model is proved to allow real-time rendering of very large and complex models with pixel-accurate details. Moreover, the necessary preprocessing is scalable and fast. For 3d point clouds, I introduce an LOD scheme based on an octree of hybrid plane-polygon representations. For each LOD, the algorithm detects planar regions in an adequately subsampled point cloud and models them as textured rectangles. The rendering of the resulting hybrid model is an order of magnitude faster than comparable point-based LOD schemes. To automatically derive a city model from a DSM, I propose a constrained mesh simplification. Apart from the geometric distance between simplified and original model, it evaluates constraints based on detected planar structures and their mutual topological relations. The resulting models are much less complex than the original DSM but still represent the characteristic building structures faithfully. Finally, I present a method to combine semantic information with complex geometric models. My approach links the semantic entities to the geometric entities on-the-fly via coarser proxy geometries which carry the semantic information. Thus, semantic information can be layered on top of complex LOD models without an explicit attribution step. All findings are supported by experimental results which demonstrate the practical applicability and efficiency of the methods

3D visualisation of oil reservoirs

This research introduces a novel approach to storing compressed 3D grid information by applying octree compression techniques. This new data structure stores the octree in a pruned flattened fashion where only header and active leaf nodes are stored in a linear array. This generates high levels of lossless compression when applied to 3D geometry where clusters of homogeneous information exist. This data structure yields fast, log(n) look-up times and initial results show that when coupled with bespoke scanning methods searching times can surpass that of direct access. Hierarchical pyramid visualisations techniques are also presented using the information stored at each level in the tree structure. Integrating with this are face culling algorithms developed in this research, which eliminate hidden face and inner leaf node cells which eases the burden placed on the CPU and GPU. By integrating these pyramid scaling and face culling algorithms, grid models can be shown at various levels of resolution incorporating sub-regions, "regions of interest" displayed at full resolution. This further lightens the load on the GPU generating quicker loading times and higher refresh rates. This can potentially allow larger models to be visualised than would otherwise have been possible. This research was sponsored by Sciencesoft an oil reservoir visualisation company and the algorithms developed in this research have been applied to compressing oil reservoir information. Oil companies require accurate 3D computer-generated models of oil reservoirs in order to make oil and gas extraction as cost effective as possible. Advances in computing power has meant that it is now possible to run multi-million cell oil reservoir grid models, increasing the level of accuracy and precision available to engineers. This thesis applies 3D octree compression techniques to these computer models and compares these with industry standard storage and cell searching algorithms as industry benchmarks. This thesis suggests that octree compression techniques may prove to be a more efficient data structure for storing and searching active cell information within oil reservoirs than existing procedures

Visualización interactiva de terrenos extensos en entornos distribuidos sobre redes mixtas P2P y cliente-servidor

En los últimos años se ha producido una gran demanda de aplicaciones dedicadas a la visualización interactiva de terrenos en entornos distribuidos. Esta demanda ha estado motivada, entre otros motivos, por el aumento de la cantidad y precisión de la información de las bases de datos del terreno y el aumento de las líneas de conexión de banda ancha y la facilidad de acceso a las mismas. Este tipo de aplicaciones tienen que hacer frente a varios problemas. Uno de ellos es la gestión de la ingente cantidad de información que contienen las bases de datos del terreno que emplean, la cual no puede ser representada simultáneamente en pantalla con una velocidad de refresco adecuada, ya que sobrepasa las capacidades de memoria y procesamiento de los equipos actuales. Otro problema es la transmisión de esa información desde los servidores a los equipos utilizados por los usuarios con la suficiente rapidez para que éstos puedan realizar una visualización interactiva en tiempo real de la misma. El último de los problemas principales es la escalabilidad del sistema con el número de usuarios. Este tipo de aplicaciones suelen tener un elevado número de usuarios conectados, incluso es previsible que a medida que las bases de datos sean más precisas y las aplicaciones más completas, este número de usuarios siga aumentando, surgiendo el problema de tener que mantener para todos ellos una calidad de servicio adecuada. A lo largo de esta tesis se ha diseñado un sistema de visualización interactiva de terrenos eficiente para entornos distribuidos que hace frente y soluciona estos problemas. Para ello se lleva a cabo un estudio de los problemas que presenta y sus posibles soluciones, escogiendo para la implementación de cada uno de los módulos en los que se divide el sistema, la solución que se ha considerado más adecuada. Así, para solucionar el problema asociado a la representación y visualización de la información del terreno, se ha encontrado un algoritmo que realiza de forma eficiente esta visualización en un entorno con bases de datos distribuidas. Para solucionar el problema asociado a la transmisión y almacenamiento de la información del terreno, se ha diseñado un nuevo esquema de compresión basado en la transformada wavelet que realiza una compresión de esta información permitiendo realizar la transmisión progresiva de la misma de forma óptima a través de la red. Por último, para solucionar el problema de la escalabilidad con el aumento del número de usuarios conectados, se ha definido una arquitectura de red híbrida basada en el funcionamiento de las arquitecturas cliente‐servidor y P2P, que incorpora las ventajas de ambas arquitecturas y evita sus inconvenientes, aumentando considerablemente la escalabilidad del sistema. Todos estos elementos se han integrado perfectamente para crear un sistema de visualización interactiva de terrenos eficiente para entornos distribuidos.In the last years there has been a great development on real time terrain visualization applications using remote databases. These kinds of applications have to face some problems, for example, a large number of users connected, data terrain visualization, storage and transmission. Despite the increase of the computers performance and connection lines capacity, the large amount of data to be managed could overload computer memory and connection lines. Moreover, the data must be stored in the client side, so they need a considerable storage space. Therefore, in this thesis we describe a new real time terrain visualization system that solves these problems. In order to solve visualization problem, we have studied different rendering algorithms and we have chosen the one that visualizes large remote terrain databases in an efficient way. In order to solve storage and transmission problem, we have designed a new compression scheme based on the wavelet transform that is able to compress and transmit large remote terrain databases in a progressive way. Finally, in order to solve scalability problem caused by the increase of connected users, we have defined a new hybrid network architecture based on client‐server and peer‐to‐peer architectures that inherits the benefits of these architectures and avoids their drawbacks, increasing system scalability. All this elements have been integrated to create an efficient real time terrain visualization system that uses remote databases