Adaptive Camera View Clustering for Fast Incremental Image-based 3D Reconstruction
Darmstadt, TU, Bachelor Thesis, 2020
Photogrammetry, more precisely image-based 3D reconstruction, is an established method for digitizing cultural heritage sites and artifacts. This method utilizes images from different perspectives to reconstruct the geometry and texture of an object. What images are necessary for a successful reconstruction depends on the size, shape, and complexity of the object. Therefore, an autonomous scanning system for 3D reconstruction requires some kind of feedback during acquisition. In this thesis, we present an evaluation of different state-of-the-art photogrammetry solutions to identify which of them is most capable of providing feedback that predicts the quality of the final 3D reconstruction during acquisition. For this, we focused on the open-source incremental reconstruction solutions COLMAP, Alicevision Meshroom and MVE. Additionally, we included the commercial solution Agisoft Metashape to evaluate how it compares against the open-source solutions. While we were able to identify some characteristic behaviors, the accuracy and runtime of all four reconstruction solutions vary based on the input dataset. Because of this, and the fact that all four solutions compute very similar results under the same conditions, our tests were not conclusive. Nevertheless, we chose COLMAP as the back-end for further use as it provided good results on the real dataset as well as an extensive command-line interface (CLI). Based on these results, we introduce an iterative image-based reconstruction pipeline that uses a cluster-based acceleration structure to deliver more robust and efficient 3D reconstructions. The photogrammetry solution used for reconstruction is exchangeable. In this pipeline, images that portray common parts of an object are assigned to clusters based on their camera frustums. Each cluster can be reconstructed separately. The pipeline was implemented as a c++ module and tested on the autonomous robotic scanner CultArm3D®. For this system, we embedded the pipeline in a feedback loop with a density-based Next-Best-View (NBV) algorithm to assist during autonomous acquisition.
End-to-end Color 3D Reproduction of Cultural Heritage Artifacts: Roseninsel Replicas
Eurographics Workshop on Graphics and Cultural Heritage (GCH) <17, 2019, Sarajevo, Bosnia and Herzegovina>
Planning exhibitions of cultural artifacts is always challenging. Artifacts can be very sensitive to the environment and therefore their display can be risky. One way to circumvent this is to build replicas of these artifacts. Here, 3D digitization and reproduction, either physical via 3D printing or virtual, using computer graphics, can be the method of choice. For this use case we present a workflow, from photogrammetric acquisition in challenging environments to representation of the acquired 3D models in different ways, such as online visualization and color 3D printed replicas. This work can also be seen as a first step towards establishing a workflow for full color end-to-end reproduction of artifacts. Our workflow was applied on cultural artifacts found around the “Roseninsel” (Rose Island), an island in Lake Starnberg (Bavaria), in collaboration with the Bavarian State Archaeological Collection in Munich. We demonstrate the results of the end-to-end reproduction workflow leading to virtual replicas (online 3D visualization, virtual and augmented reality) and physical replicas (3D printed objects). In addition, we discuss potential optimizations and briefly present an improved state-of-the-art 3D digitization system for fully autonomous acquisition of geometry and colors of cultural heritage objects.
Acceleration of 3D Mass Digitization Processes: Recent Advances and Challenges
Mixed Reality and Gamification for Cultural Heritage
In the heritage field, the demand for fast and efficient 3D digitization technologies for historic remains is increasing. Besides, 3D has proven to be a promising approach to enable precise reconstructions of cultural heritage objects. Even though 3D technologies and postprocessing tools are widespread and approaches to semantic enrichment and Storage of 3D models are just emerging, only few approaches enable mass capture and computation of 3D virtual models from zoological and archeological findings. To illustrate how future 3D mass digitization systems may look like, we introduce CultLab3D, a recent approach to 3D mass digitization, annotation, and archival storage by the Competence Center for Cultural Heritage Digitization at the Fraunhofer Institute for Computer Graphics Research IGD. CultLab3D can be regarded as one of the first feasible approaches worldwide to enable fast, efficient, and cost-effective 3D digitization. lt specifically designed to automate the entire process and thus allows to scan and archive large amounts of heritage objects for documentation and preservation in the best possible quality, taking advantage of integrated 30 visualization and annotation within regular Web browsers using technologies such as WebGI and X3D.
Methodology for Evaluation of Precision and Accuracy of Different Geometric 3D Data Acquisition Methods
München, TU, Master Thesis, 2017
3D optical scanning systems have been gaining considerable space in metrology, being largely applied in industry sectors and in the cultural heritage domain. The amount of available sensors on the market has grown considerably. Thereby, deciding for the right technique that fits-to-a-purpose or the most cost efficient technology, is a challenging task. When deciding in which technology to invest, the user often relies on the manufacturer’s instructions. However, manufacturers generally do not state under which conditions such values were acquired and thus, the system’s reproducibility is not assured. If measurements could be traced back to a common standard, this problem could be easily addressed. As such a solution is still not available, specialist often tend to solve this issue by associating terms like precision, accuracy and uncertainty to a measurement. Nowadays, the most applicable solution to define the accuracy of a system relies on the VDI/VDE 2634. This master thesis aims to develop a common solution to assess accuracy for different geometric 3D data acquisition models, considering the specifications of the VDI/VDE 2634 Part 3. The methodology proposed here encompasses the entire process from the acquisition to its processing stage. The study-case comprehend triangulated methods, as photogrammetry and laser line sensor. During the acquisition, a calibrated probing body and adapted test are proposed. The processing stage includes a best-fit algorithm and an evaluation of measurement uncertainty. The result comprehends the quality parameters together with the visualization of measurement uncertainty supporting the entire system. Therefore, providing to the end user enough information about the capability of the evaluated system.
Projecting our Past to the Future - Challenges and Results: The Case of Asinou Church
Eurographics Workshop on Graphics and Cultural Heritage (GCH) <15, 2017, Graz, Austria>
In this paper, we present some of the novel results of the Marie Curie Initial Training Network for Digital Cultural Heritage (ITN-DCH) project, describing briefly the work done focusing on the project's first case study: the Panagia Phorviotisa of Asinou, an UNESCO World Heritage Listed (WHL) monument in Cyprus. The paper introduces some challenges and the importance of multidisciplinary, sustainable research and development in the emerging domain of DCH in Europe. The different methodologies address these challenges through a professional network of partners including Academia, Research and Industry. The paper describes the 3D documentation of the church and how the data acquired can be used and re-used in Mixed Reality (MR) applications using also Deep Learning techniques, as well as in Education.
c-Space: Time-evolving 3D Models (4D) from Heterogeneous Distributed Video Sources
Eurographics Workshop on Graphics and Cultural Heritage (GCH) <14, 2016, Genova, Italy>
We introduce c-Space, an approach to automated 4D reconstruction of dynamic real world scenes, represented as time-evolving 3D geometry streams, available to everyone. Our novel technique solves the problem of fusing all sources, asynchronously captured from multiple heterogeneous mobile devices around a dynamic scene at a real word location. To this end all captured input is broken down into a massive unordered frame set, sorting the frames along a common time axis, and finally discretizing the ordered frame set into a time-sequence of frame subsets, each subject to photogrammetric 3D reconstruction. The result is a time line of 3D models, each representing a snapshot of the scene evolution in 3D at a specific point in time. Just like a movie is a concatenation of time-discrete frames, representing the evolution of a scene in 2D, the 4D frames reconstructed by c-Space line up to form the captured and dynamically changing 3D geometry of an event over time, thus enabling the user to interact with it in the very same way as with a static 3D model. We do image analysis to automatically maximize the quality of results in the presence of challenging, heterogeneous and asynchronous input sources exhibiting a wide quality spectrum. In addition we show how this technique can be integrated as a 4D reconstruction web service module, available to mobile end-users.
Data Provenance in Photogrammetry Through Documentation Protocols
XXIII ISPRS Congress Prague, Commission V
International Society for Photogrammetry and Remote Sensing Congress (ISPRS) <23, 2016, Prague, Czech Republic>
ISPRS Annals of the Photogrammetry, Remote Sensing and Spatial Information Sciences, III-5
Documenting the relevant aspects in digitisation processes such as photogrammetry in order to provide a robust provenance for their products continues to present a challenge. The creation of a product that can be re-used scientifically requires a framework for consistent, standardised documentation of the entire digitisation pipeline. This article provides an analysis of the problems inherent to such goals and presents a series of protocols to document the various steps of a photogrammetric workflow. We propose this pipeline, with descriptors to track all phases of digital product creation in order to assure data provenance and enable the validation of the operations from an analytic and production perspective. The approach aims to support adopters of the workflow to define procedures with a long term perspective. The conceptual schema we present is founded on an analysis of information and actor exchanges in the digitisation process. The metadata were defined through the synthesis of previous proposals in this area and were tested on a case study. We performed the digitisation of a set of cultural heritage artefacts from an Iron Age burial in Ilmendorf, Germany. The objects were captured and processed using different techniques, including a comparison of different imaging tools and algorithms. This augmented the complexity of the process allowing us to test the flexibility of the schema for documenting complex scenarios. Although we have only presented a photogrammetry digitisation scenario, we claim that our schema is easily applicable to a multitude of 3D documentation processes.