Markus Grabner

3D MURALE: a multimedia system for archaeology

This paper introduces the 3D Measurement and Virtual Reconstruction of Ancient Lost Worlds of Europe system (3D MURALE). It consists of a set of tools for recording, reconstructing, encoding, visualising and database searching/querying that operate on buildings, building parts, statues, statue parts, pottery, stratigraphy, terrain geometry and texture and material texture. The tools are loosely linked together by a common database on which they all have the facility to store and access data. The paper describes the overall architecture of the 3D MURALE system and then briefly describes the functionality of the tools provided by the project. The paper compares the multimedia studio architecture adopted in this project with other multimedia studio architectures.

Ray casting of multiple volumetric datasets with polyhedral boundaries on manycore GPUs

We present a new GPU-based rendering system for ray casting of multiple volumes. Our approach supports a large number of volumes, complex translucent and concave polyhedral objects as well as CSG intersections of volumes and geometry in any combination. The system (including the rasterization stage) is implemented entirely in CUDA, which allows full control of the memory hierarchy, in particular access to high bandwidth and low latency shared memory. High depth complexity, which is problematic for conventional approaches based on depth peeling, can be handled successfully. As far as we know, our approach is the first framework for multivolume rendering which provides interactive frame rates when concurrently rendering more than 50 arbitrarily overlapping volumes on current graphics hardware.

Automatic differentiation for GPU-accelerated 2D/3D registration

A common task in medical image analysis is the alignment of data from different sources, e.g., X-ray images and computed tomography (CT) data. Such a task is generally known as registration. We demonstrate the applicability of automatic differentiation (AD) techniques to a class of 2D/3D registration problems which are highly computationally intensive and can therefore greatly benefit from a parallel implementation on recent graphics processing units (GPUs). However, being designed for graphics applications, GPUs have some restrictions which conflict with requirements for reverse mode AD, in particular for taping and TBR analysis. We discuss design and implementation issues in the presence of such restrictions on the target platform and present a method which can register a CT volume data set (512 × 512 × 288 voxels) with three X-ray images (512 × 512 pixels each) in 20 seconds on a GeForce 8800GTX graphics card.

A work-flow and data model for reconstruction, management, and visualization of archaeological sites

We propose a framework for a complex visualization environment suitable for archaelogical applications. Given 2D and 3D data derived from appropriate acquisition processes, the scene is organized in a structure that can easily be incorporated into a database. Special care is taken on attributes such as time and likelihood of scientific hypothesises which are important for a correct interpretation of the excavation site. After a preprocessing step, the database content can directly be used to visualize the scene in a standalone virtual reality installation in a museum as well as on the internet.

Fast Marker Based C-Arm Pose Estimation

To estimate the pose of a C-Arm during interventions therapy we have developed a small sized X-Ray Target including a special set of beads with known locations in 3D space. Since the patient needs to remain in the X-Ray path for all feasible poses of the C-Arm during the intervention, we cannot construct a single marker which is entirely visible in all images. Therefore finding 2D-3D point correspondences is a non-trivial task. The marker pattern has to be chosen in a way such that its projection onto the image plane is unique in a minimal-sized window for all relevant poses of the C-Arm. We use a two dimensional adaption of a linear feedback shift register (LFSR) to generate a two-dimensional pattern with unique sub-patterns in a certain window range. Thereby uniqueness is not achieved by placing unique 2D sub patterns side by side but by the code property itself. The code is designed in a way that any sub window of a minimal size guarantees uniqueness and that even occlusions from medical instruments can be handled. Experiments showed that we were able to estimate the C-Arms pose from a single image within one second with a precision below one millimeter and one degree.

Image Space Advection on graphics hardware

The scientific visualization and computer graphics communities have witnessed a tremendous rise in graphics processing unit (GPU) related literature and methodology recently. This is due in part to the rapidly increasing processing speed offered by graphics cards. Parallel to this, we have seen several advances made in the area of texture-based flow visualization. We present a texture-based flow visualization technique, Image Space Advection (ISA), that takes advantage of the computing power offered by recent, state-of-the-art GPUs. We have implemented a completely GPU-based version of the ISA algorithm. Here we describe our implementation in detail, including both the advantages and disadvantages of implementing ISA on the GPU. The result is state-of-the-art technique that demonstrates the latest in terms of both flow visualization methodology and GPU programming.

Providing multimedia tools for recording, reconstruction, visualisation and database storage/access of archaeological excavations

Over the years archaeologists have been swift to embrace new advances in technology that allow them to more comprehensively document the results of their work. Today it is commonplace to find information technologies, in the form MS Office-type tools with some CAD and GIS, deployed for primary data capture, analysis, presentation and publication. While these computing technologies can be used effectively to record and interpret archaeological sites, the radical developments in 3D recording, reconstruction and visualisation tools have had relatively limited impact upon the archaeological community. This is unfortunate as these new technologies have the potential to (a) enable the archaeologists to record their unrepeatable experiments to unprecedented levels of accuracy, (b) enable the archaeologists to reconstruct artefacts such as pottery from sherds, textures and sites from different eras (c) visualise the wealth of excavated information in dynamic new ways away from the archaeological site during post-excavation analysis, (d) make this wealth of detail available to the scholarly community as part of the publication process and secure its digital longevity through its deposition in a trusted digital library/archive and (e) communicate the excitement and importance of their archaeological site and its finds to an interested non-academic audience. This paper describes the overall concept of the EU funded project, 3D Measurement and Virtual Reconstruction of Ancient Lost Worlds of Europe (3D MURALE), that has developed and created a set of low-cost multimedia tools for recording, reconstructing, encoding, and visualising archaeological artefacts and site.

Modeling and visualizing the cultural heritage data set of Graz

The inner city (Old Town) of Graz will be the European cultural capital in 2003. In this paper we present preliminary results on the reconstruction and visualization of this kind of cultural heritage data. Starting with a simple block model obtained by converting 2 1/2 dimensional GIS (geographic information system) data we focus on the image based modeling of the facades. Herein we illustrate a robust search for corresponding points to estimate the relative orientation between image pairs.Additional, we outline our real-time rendering approach based on a LOD-R-tree concept. Special attention is paid on the LOD (level of detail) generation for historic buildings where two different ways working in 2D and 3D are explained. The visualization system is communicating asynchronously with a database system storing the LOD-R-tree data structure. This client-server configuration provides interactive navigation through the virtual scene and the scalability of a database management system.

Smooth High-Quality Interactive Visualization

The paper addresses the problem of interactive visualization in the view-dependent simplification framework. A geomorphing algorithm for interpolation between different levels of detail is given. The interpolation parameter is derived from the screen-space geometric error instead of assigning a fixed transition time to the interpolation process. Furthermore, a hybrid frame rate control system is proposed. Frame time is predicted based on the average rendering time per triangle, reducing oscillation and overshooting. A set of experiments demonstrates the advantages of both methods.

A Variational Approach to Semiautomatic Generation of Digital Terrain Models

We present a semiautomatic approach to generate high quality digital terrain models (DTM) from digital surface models (DSM). A DTM is a model of the earths surface, where all man made objects and the vegetation have been removed. In order to achieve this, we use a variational energy minimization approach. The proposed energy functional incorporates Huber regularization to yield piecewise smooth surfaces and an L1 norm in the data fidelity term. Additionally, a minimum constraint is used in order to prevent the ground level from pulling up, while buildings and vegetation are pulled down. Being convex, the proposed formulation allows us to compute the globally optimal solution. Clearly, a fully automatic approach does not yield the desired result in all situations. Therefore, we additionally allow the user to affect the algorithm using different user interaction tools. Furthermore, we provide a real-time 3D visualization of the output of the algorithm which additionally helps the user to assess the final DTM. We present results of the proposed approach using several real data sets.