Mona Hess

Towards fully automatic reliable 3D acquisition

This paper describes a novel system for accurate 3D digitization of complex objects. Its main novelties can be seen in the new approach, which brings together different systems and tools in a unique platform capable of automatically generating an accurate and complete model for an object of interest. This is performed through generating an approximate model of the object, designing a stereo imaging network for the object with this model and capturing the images at the designed postures through exploiting an inverse kinematics method for a non-standard six degree of freedom robot. The images are then used for accurate and dense 3D reconstruction using photogrammetric multi-view stereo method in two modes, including resolving scale with baseline and with control points. The results confirm the feasibility of using Particle Swarm Optimization in solving inverse kinematics for this non-standard robot. The system provides this opportunity to test the effect of incidence angle on imaging network design and shows that the matching algorithms work effectively for incidence angle of 10?. The accuracy of the final point cloud generated with the system was tested in two modes through a comparison with a dataset generated with a close range 3D colour laser scanner. We designed a 6-DOF robot for accurate and dense 3D reconstruction using images.Particle Swarm Optimization was evaluated for inverse kinematic of the robot.A software package, Imaging Network Designer, was tested for this robot.The accuracy of the robot for 3D reconstruction is around 200 µ m .

Well Connected to Your Digital Object? E-Curator: A Web-based e-Science Platform for Museum Artefacts

This article describes the development of a new virtual research tool for the Arts and Humanities community. The E-Curator project led by Museums and Collections at University College London took a practical, multidisciplinary approach to traceable storage and transmission of three-dimensional (3D) laser scan data sets. The objective was to establish protocols for retrievable data acquisition and processing to facilitate remote web-based access to museum e-artefacts and thereby enhance international scholarship. An Internet capable 3D visualization tool was designed, using state-of-the-art colour laser scanning technology for digitizing museum objects in combination with an e-science developed data storage and retrieval solution (Storage Resource Broker). The prototype was developed in discussion with a team of museum curators and conservators who were able to compare the handling of a range of real objects with their virtual copies on-screen. This article will explore two case studies of objects recorded with an Arius3D colour laser scanner and a handheld Metris K-Scan laser scanner to illustrate the 3D recording methodology and highlight how the developed system is capable of complementing traditional cataloguing and analysis methods for museum artefacts and enable digital repatriation. Anthropological research, based on observations from the example of the E-Curator project, is discussing the production, reception, and circulation of 3D digital objects and the networked technology of the digital image.

Automatic Image Selection in Photogrammetric Multi-view Stereo Methods

This paper brings together a team of specialists in optical metrology, museum curation, collection digitization and 3D development to describe and illustrate by example a method for the selection of the most suitable camera views, vantage viewpoints, from a large image dataset intended for metric 3D artefact reconstruction. The presented approach is capable of automatically identifying and processing the most appropriate images from a multi-image photogrammetric network captured by an imaging specialist. The aim is to produce a 3D model suited to a wide range of museum uses, including visitor interactives. The approach combines off-the-shelf imaging equipment with rigorous photogrammetric bundle adjustment and multi-view stereo (MVS), supported by an image selection process that is able to take into account range-related and visibility-related constraints. The paper focusses on the two key steps of image clustering and iterative image selection. The developed method is illustrated by the 3D recording of four ancient Egyptian artefacts from the Petrie Museum of Egyptian Archaeology at UCL, with an analysis taking into account completeness, coordination uncertainty and required number of images. Comparison is made against the baseline of the established CMVS (Clustering Views for Multi-view Stereo), which is a free package for selecting vantage images within a huge image collection. For the museum, key outputs from the 3D recording process are visitor interactives which are built around high quality textured mesh models. The paper therefore considers the quality of the output from each process as input to texture model generation. Results demonstrate that whilst both methods can provide high quality records, our new method, Image Network Designer (IND), can provide a better image selection for MVS than CMVS in terms of coordination uncertainty and completeness of the final model for the museum recording of artefacts. Furthermore, the improvements gained, particularly in model completeness, minimise the significant overhead in mesh editing needed to provide a more direct and economical route to 3D model output.

Niabara - The Western Solomon Islands War Canoe at the British Museum - 3D Documentation, Virtual Reconstruction and Digital Repatriation

This paper describes the 3D digital documentation of a highly significant cultural heritage object from the Melanesian Southwest Pacific, held in the ethnographic collections of the British Museum. The object, which dates from about 1910, is a large plank-built war canoe from the island of Vella Lavella in New Georgia, Solomon Islands. 3D laser scanning is paired with anthropological research, which aims to deliver a holistic virtual 3D reconstruction and multimedia interactive delivery of the boat for the digital repatriation to the source community.

Use of 3D laser scanning for monitoring the dimensional stability of a Byzantine ivory panel

Abstract The British Museum has in its collections a magnificent Byzantine ivory panel. However, the panel has become warped over time and there is a join on the left side, where it has suffered a break in the past. It has been connected with two metal pins and adhesive in a previous conservation treatment but there is now concern that these could be having an adverse influence on natural movements within the ivory. Given the importance of the panel, the decision was made to leave the pins in place and monitor the stability of the panel. As the geometry of the panel is complex, it was felt that microscopic imaging would not be suitable and 3D laser scanning was used instead. This engineering metrology technique is increasingly used in cultural heritage and conservation to record minute three-dimensional changes with high spatial accuracy. The resulting dataset is a detailed metric 3D record of the object surface in-the-round and comparison of subsequent scans with a reference scan can indicate dimensional changes. As part of a monitoring campaign, the ivory panel was first scanned in January 2012 to provide a reference scan. It was then scanned again in autumn 2012 (no significant movement was detected) and will be scanned at regular intervals in the future. This case study demonstrates the potential of 3D laser scanning to monitor the dimensional stability of complex artefacts.

Improving automated 3D reconstruction methods via vision metrology

This paper aims to provide a procedure for improving automated 3D reconstruction methods via vision metrology. The 3D reconstruction problem is generally addressed using two different approaches. On the one hand, vision metrology (VM) systems try to accurately derive 3D coordinates of few sparse object points for industrial measurement and inspection applications; on the other, recent dense image matching (DIM) algorithms are designed to produce dense point clouds for surface representations and analyses. This paper strives to demonstrate a step towards narrowing the gap between traditional VM and DIM approaches. Efforts are therefore intended to (i) test the metric performance of the automated photogrammetric 3D reconstruction procedure, (ii) enhance the accuracy of the final results and (iii) obtain statistical indicators of the quality achieved in the orientation step. VM tools are exploited to integrate their main functionalities (centroid measurement, photogrammetric network adjustment, precision assessment, etc.) into the pipeline of 3D dense reconstruction. Finally, geometric analyses and accuracy evaluations are performed on the raw output of the matching (i.e. the point clouds) by adopting a metrological approach. The latter is based on the use of known geometric shapes and quality parameters derived from VDI/VDE guidelines. Tests are carried out by imaging the calibrated Portable Metric Test Object, designed and built at University College London (UCL), UK. It allows assessment of the performance of the image orientation and matching procedures within a typical industrial scenario, characterised by poor texture and known 3D/2D shapes.

Practice-Based Comparison of Imaging Methods for Visualization of Toolmarks on an Egyptian Scarab

3D representations were made of a small Egyptian scarab with a gold band by a number of methods, based on photogrammetry and photometric stereo. They were evaluated for colour fidelity and spatial detail, in the context of a study of toolmarks and manufacturing techniques of jewellery in ancient Egypt. It was found that although a 3D laser scanner gave the best geometric accuracy, the camera-based methods of photogrammetry and photometric stereo gave better representation of fine detail and colour on the object surface.

Three-dimensional reconstruction of Roman coins from photometric image sets

Abstract. A method is presented for increasing the spatial resolution of the three-dimensional (3-D) digital representation of coins by combining fine photometric detail derived from a set of photographic images with accurate geometric data from a 3-D laser scanner. 3-D reconstructions were made of the obverse and reverse sides of two ancient Roman denarii by processing sets of images captured under directional lighting in an illumination dome. Surface normal vectors were calculated by a “bounded regression” technique, excluding both shadow and specular components of reflection from the metallic surface. Because of the known difficulty in achieving geometric accuracy when integrating photometric normals to produce a digital elevation model, the low spatial frequencies were replaced by those derived from the point cloud produced by a 3-D laser scanner. The two datasets were scaled and registered by matching the outlines and correlating the surface gradients. The final result was a realistic rendering of the coins at a spatial resolution of 75  pixels/mm (13-μm spacing), in which the fine detail modulated the underlying geometric form of the surface relief. The method opens the way to obtain high quality 3-D representations of coins in collections to enable interactive online viewing.

Online survey about current use of 3D imaging and its user requirements in cultural heritage institutions

The potential of 3D images is increasingly recognized by heritage professionals for opening up new technological possibilities for digital documentation, analysis and research, exhibition display and education. Yet, currently there is no comprehensive understanding of what constitute 3D image qualities for a digital artefact, from the point of view of a heritage professional. An online survey addressed to the international heritage community gauged information about current adoption of 3D imaging technologies, priorities for 3D image quality and visions of future use. Despite a number of barriers, there is a high interest in 3D imaging technologies across heritage institutions and the museum sector.

Application of multi-modal 2D and 3D imaging and analytical techniques to document and examine coins on the example of two Roman silver denarii

This case study is applying imaging and analytical techniques from multiple scientific disciplines to digitise coins and evaluate 3D multi-modal visualisation. Two ancient Roman silver denarii were selected as test objects to establish whether the proposed digital recording methods can support professional numismatic comparison of features and properties. The coins raise questions concerning their provenance, authenticity, design, purpose of issue and historic usage, but they also pose considerable recording challenges due to their material and surface properties, which are the main focus in this paper. The coins have been examined by the following techniques: dome photography for image sets for PTM/RTI visualisation and photometric stereo; X-ray microtomography for detection of cracks or impurities; Scanning Electron Microscopy for detailed surface investigation; Energy-Dispersive X-ray Spectroscopy for elemental analysis; micro X-ray fluorescence spectrometry mapping; 3D laser and structured light scanning for 3D spatial capture; photogrammetry/structure from motion, focus-stacking. The results indicate the feasibility of such techniques for museum documentation and as contribution to scientific examination of coins in general.