Establishing Best Practices for Photogrammetric Recording During Archaeological Fieldwork

Archaeologists have recently embraced photogrammetry as a low-cost, efficient tool for recording archaeological artifacts, active excavation contexts, and architectural remains. However, no consensus has yet been reached about standard procedures for reliable and metrically accurate photogrammetric recording. The archaeological literature describes diverse equipment and approaches to photogrammetry. The purpose of this article is to open a discussion about when and how photogrammetry should be employed in archaeology in an effort to establish “best practices” for this new method. We focus on the integration of photogrammetry within a comprehensible research plan, the selection of equipment, the appropriate apportionment of labor and time on site, and a rubric for site photography that is conducive to successful and efficient modeling. We conclude that photogrammetric modeling will soon become an indispensable tool in most archaeological applications but should always be implemented in ways that do not place undue burdens on project personnel and budgets and that aid research goals in well-defined ways.     

Computer vision methods and rock art: towards a digital detection of pigments

A non-invasive procedure for assessing and interpreting the pigments of rock art paintings through computer vision and photogrammetric techniques is presented. The method is designed to document and interpret poorly preserved pigments by making use of advanced techniques of photogrammetry and computational imaging. Two different software solutions that were developed by the authors have been used for this purpose. Finally, two case studies of rock art paintings from Spain have been analysed, which show the reliability of the method.     

Surfaces from the Visual Past: Recovering High<Emphasis Type="Bold">-</Emphasis>Resolution Terrain Data from Historic Aerial Imagery for Multitemporal Landscape Analysis

Historic aerial images are invaluable sources of aid to archaeological research. Often collected with large-format photogrammetric quality cameras, these images are potential archives of multidimensional data that can be used to recover information about historic landscapes that have been lost to modern development. However, a lack of camera information for many historic images coupled with physical degradation of their media has often made it difficult to compute geometrically rigorous 3D content from such imagery. While advances in photogrammetry and computer vision over the last two decades have made possible the extraction of accurate and detailed 3D topographical data from high-quality digital images emanating from uncalibrated or unknown cameras, the target source material for these algorithms is normally digital content and thus not negatively affected by the passage of time. In this paper, we present refinements to a computer vision-based workflow for the extraction of 3D data from historic aerial imagery, using readily available software, specific image preprocessing techniques and in-field measurement observations to mitigate some shortcomings of archival imagery and improve extraction of historical digital elevation models (hDEMs) for use in landscape archaeological research. We apply the developed method to a series of historic image sets and modern topographic data covering a period of over 70 years in western Sicily (Italy) and evaluate the outcome. The resulting series of hDEMs form a temporal data stack which is compared with modern high-resolution terrain data using a geomorphic change detection approach, providing a quantification of landscape change through time in extent and depth, and the impact of this change on archaeological resources.     

Image‐Based Modelling from Unmanned Aerial Vehicle (UAV) Photogrammetry: An Effective,Low‐Cost Tool for Archaeological Applications

The recording and 3D modelling of complex archaeological sites is usually associated with high capital and logistical costs, because the data acquisition must be performed by specialists using expensive surveying sensors (i.e., terrestrial laser scanners, robotic total stations and/or ground‐penetrating radar). This paper presents a novel, low‐cost, user‐friendly photogrammetric tool for generating high‐resolution and scaled 3D models of complex sites. The results obtained with unmanned aerial vehicle (UAV) photogrammetry of an archaeological site indicate that this approach is semi‐automatic, inexpensive and effective, and that it guarantees quality.     

Mapping by matching: a computer vision-based approach to fast and accurate georeferencing of archaeological aerial photographs

To date, aerial archaeologists generally apply simple rectification procedures or more expensive and time-consuming orthorectification algorithms to correct their aerial photographs in varying degrees for geometrical deformations induced by the topographical relief, the tilt of the camera axis and the distortion of the optics. Irrespective of the method applied, the georeferencing of the images is commonly determined with ground control points, whose measurement and identification is a time-consuming operation and often limits certain images from being accurately georeferenced. Moreover, specialised software, certain photogrammetric skills, and experience are required. Thanks to the recent advances in the fields of computer vision and photogrammetry as well as the improvements in processing power, it is currently possible to generate orthophotos of large, almost randomly collected aerial photographs in a straightforward and nearly automatic way. This paper presents a computer vision-based approach that is complemented by proven photogrammetric principles to generate orthophotos from a range of uncalibrated oblique and vertical aerial frame images. In a first phase, the method uses algorithms that automatically compute the viewpoint of each photograph as well as a sparse 3D geometric representation of the scene that is imaged. Afterwards, dense reconstruction algorithms are applied to yield a three-dimensional surface model. After georeferencing this model, it can be used to create any kind of orthophoto out of the initial aerial views. To prove the benefits of this approach in comparison to the most common ways of georeferencing aerial imagery, several archaeological case studies are presented. Not only will they showcase the easy workflow and accuracy of the results, but they will also prove that this approach moves beyond current restrictions due to its applicability to datasets that were previously thought to be unsuited for convenient georeferencing.     

Combining photogrammetry and laser scanning for the recording and modelling of the Late Intermediate Period site of Pinchango Alto,Palpa, Peru

This paper describes the 3D modelling of Pinchango Alto, Peru, based on a combination of image and range data. Digital photogrammetry and laser scanning allow archaeological sites to be recorded efficiently and in detail even under unfavourable conditions. In 2004 we documented Pinchango Alto, a typical site of the hitherto poorly studied Late Intermediate Period on the south coast of Peru, with the aim of conducting spatial archaeological analyses at different scales. The combined use of a mini helicopter and a terrestrial laser scanner, both equipped with a camera, allowed a fast yet accurate recording of the site and its stone architecture. In this paper we describe the research background, the 3D modelling based on different image and range data sets, and the resulting products that will serve as a basis for archaeological analysis.     

Towards a Risk Management and Conservation Plan for the Djin Blocks at the World Heritage Site of Petra,Jordan: The Case of Djin Block No. 9

Cultural heritage is subjected to many pressures and risks. Over the past few years, the use of digital technologies has significantly changed the approaches to cultural heritage documentation for the purpose of condition assessment and conservation. The integration of novel approaches and techniques has permitted a detailed examination and assessment of damage, deterioration due to weathering and erosion, and their mechanisms. This study seeks to contribute to the preservation and conservation of the significant heritage of the so-called Djin Blocks at the World Heritage Site of Petra in Jordan. While these three dimensional cuboid rock-cut monuments have been subject to extensive conservation studies, this is the first time they have been subjected to 3D recording and multispectral photography, with the aim of recording damage caused by the ravages of time.

This study presents the results of the documentation of the case study Djin Block No. 9. A variety of systematic documentation techniques were used, including 3D recording with terrestrial laser scanning (TLS), close-range photogrammetry, multispectral imaging, and thermography records. In addition, pathological studies of the erosion from various causes and an analysis of the effect of weathering on Djin Block No. 9 are performed. Based on this data, the paper presents recommendations for developing risk management and conservation planning of Djin Block No. 9.     

New tools for rock art modelling: automated sensor integration in Pindal Cave

This paper presents the integration of automated sensors based on a terrestrial laser scanner and an amateur digital camera with the aim of generating a photorealistic three-dimensional (3D) model of the Principal Panel in Pindal Cave (Spain). The approach developed for 3D modelling overcomes many of the problems related to the independent implementation of photogrammetry and laser scanning. Particularly, a sequential and hierarchical approach was developed based on the processing and matching of images from the camera (camera image) and the laser scanner (range image). The results obtained demonstrate that the workflow for this model is automatic, effective, and accurate. The presented approach was found to create hyper-realistic models, even improving upon human visual capabilities.     

A HYBRID APPROACH TO CREATE AN ARCHAEOLOGICAL VISUALIZATION SYSTEM FOR A PALAEOLITHIC CAVE

This paper presents a visualization system based on metric data to manage and disseminate archaeological information on the Internet. We describe the integration of two different types of sensors: laser scanning and close‐range photogrammetry. How we created an automatic and hierarchical approach based on processing and matching the images coming from a digital camera and a terrestrial laser scanner is also shown. This development has created a visualization system combining spherical photographs and georeferences for graphical and numerical data acquired by the sensors. The case study where we have applied this method is the Palaeolithic rock art of the Llonín Cave (Asturias, Spain), which has been declared a World Heritage Site by UNESCO and has restricted public access. Our results demonstrate that this tool integrates data, metadata, services and information, which simplifies the location, identification, selection and management of archaeological information.     

The use of stereoscopic images taken from a microdrone for the documentation of heritage – An example from the Tuekta burial mounds in the Russian Altay

To analyse, interpret and manage our cultural heritage it is important to have an accurate and realistic representation of it. Documenting this heritage involves geographic techniques such as photogrammetry, for which a lot of rather expensive and extensive platforms are already in use. However, a microdrone, a recently developed unmanned aerial vehicle platform is a cheaper and easy to handle tool. To test the very limits of the microdrone and its accompanying data-acquisition and data-processing software, we collected data from a remote area in Tuekta, in the Russian Altay Mountains. This paper presents the challenges faced during the whole photogrammetric procedure from planning the flights to producing the final deliverables.     

Digital Photogrammetry for Documentation of Maritime Heritage

Documentation of maritime heritage is essential for its protection, and for reference in restoration and renovation processes. These functions become problematic in the case of historical ships and boats that lack lines drawings. The purpose of this paper is to describe a procedure for creation of lines drawings based on the shape analysis of surviving historical boats or their small-scale models with the help of reverse engineering (RE) techniques. The paper describes how digital photogrammetry and the iterative method were used to analyze the shape of three historical boats: Tomahawk, Refola and Nada. The application of the proposed procedure produced the lines drawings of the boats as its result. The accuracy of the 3D CAD model obtained with the photogrammetric technique was verified by comparing it against a more accurate 3D model produced with the help of a RE laser scanner. The examination of the resulting lines drawings proves that the digital photogrammetry process and the proposed iterative method are adequate tools for developing lines plans of boat models. The research offers the methodological basis for the creation of an archive of lines drawings of historical boats. Such an archive would provide reference for philologically correct restorations, and permit definition and classification of distinctive elements of various types of historical boats, particularly those produced in the Campania Region.     

Archaeological Site Information Modelling and Management Based on Close-Range Photogrammetry and GIS

New challenges in management and restoration of archaeological sites require the utilization of advanced technologies and systems to assist in preserving the important legacy of human heritage. These challenges include monitoring and preserving of site landscapes, maintenance and rehabilitation of archaeological structures, and quality and safety management. In this research, an integrated methodology based on photogrammetry and Three-Dimensional (3D) Geographic Information System (GIS) is developed to capture and model essential details needed for the proper management of archaeological sites. Recent advances in digital imagery and modelling utilize photogrammetry as an efficient technique for 3D modelling of archaeological sites to derive accurate measurements of size, shape, position, and texture of objects using two-dimensional digital photographs. Spatial data that include aerial stereo photographs, satellite images, close-range photos, terrestrial surveying and Global Positioning Systems (GPS) are integrated within the design of the proposed model. The approach is validated with a case study of Ajloun Castle, one of the ancient and important preserved structures located in Jordan. Various sequential levels of details have been developed for the castle: Orthophoto, Digital Elevation Model (DEM), structures geometry and site layout and 3D textured model. The suggested methodology is expected to be efficient in modelling and documenting archaeological structures. The developed model is utilized to assess the management of archaeological structures through feasibility analysis, rehabilitation decisions, and safety planning.     

Method for photogrammetric surveying of archaeological sites with light aerial platforms

In this paper, we describe a complete methodology for performing photogrammetric surveying of archaeological sites using light aerial platforms or unmanned aerial vehicle (UAV) systems. Traditionally, the main problem with using these platforms is the irregular geometry of the photographs obtained. These irregular image block patterns are occasioned by uncontrolled circumstances (e. g. effect of wind, lack of flight control, etc.) which generate high imprecision in the positioning of camera stations. The method proposed here allows the execution of the photogrammetric flight following the predicted parameters determined in mission planning (camera focal length, photo scale, ground sample distance -GSD-, overlaps, etc.) so we can obtain regular flight geometries. Our method allows the use of conventional photogrammetric data reduction methods based on the use of stereoscopic photogrammetric workstations. Although flights with irregular patterns can allow the formation of stereo pairs within certain limits, conventional photogrammetric procedures often have great difficulty in processing these irregular image blocks. For this reason this system raises the staking out of the camera positions by using a robotized total station and a mini prism situated on the platform. This method is applied to a real photogrammetric survey of an archaeological site of the Tartessic epoch in Southern Spain. The results obtained, confirmed by a quality control of the photogrammetric flight, have demonstrated the viability of this methodology even when moderate wind effects appear.     

Toward Hybrid Modeling and Automatic Planimetry for Graphic Documentation of the Archaeological Heritage: The Cortina Family Pantheon in the Cemetery of Valencia

ABSTRACT

The current trend toward the hybrid methodology of combining terrestrial laser scanner (TLS) with close-range and UAV-assisted photogrammetry is becoming the most effective method for the complete capture of archaeological sites. In this article, we consider three objectives in this regard: first, to check an integration procedure, based on different capture techniques, to obtain the best possible complete digital model in different situations related to size, lighting, and occlusions. Second, a “laser scanning with the help of photogrammetry” strategy for the operation with the different data sources, which allows to adapt the processes of photogrammetric orientation, cloud registration, and automatic texturing, to the characteristics of each capture model. Finally, to present the digital edition of these models through automatic technical projections and realistic visualizations, to show their ability to interpret their geometry or share their knowledge, respectively.     

Experiencing Ancient Buildings from a 3D GIS Perspective: a Case Drawn from the Swedish Pompeii Project

In recent times, archaeological documentation strategies have been considerably improved by the use of advanced 3D acquisition systems. Laser scanning, photogrammetry and computer vision techniques provide archaeologists with new opportunities to investigate and document the archaeological record. In spite of this, the amount of data collected and the geometrical complexity of the models resulting from such acquisition processes have always prevented their systematic integration into a geographic information systems (GIS) environment. Recent technological advances occurred in the visualization of 3D contents, led us to overcome the aforementioned limitations and set up a work pipeline in which was possible to put the 3D models not only in the context of data visualization but also in the frame of spatial analysis. The case study described is a part of the Swedish Pompeii Project, a research and fieldwork activity started in 2000 with the purpose of recording and investigating an entire Pompeian city block, Insula V 1. As an additional part of the research, a laser scanning acquisition campaign was conducted in the last few years. The resulting models were thus meant to be used to develop further research lines: Among these, a 3D GIS system was expected to be set up with the purpose to (i) collect in the same geo-referenced environment, different typologies of documentation gathered in the context of the Swedish Pompeii Project; (ii) inter-connect 3D models with the project website; (iii) use the third dimension as a further analytical field of investigation, in the form of spatial analysis and cognitive simulation.     

A simple methodology for recording petroglyphs using low-cost digital image correlation photogrammetry and consumer-grade digital cameras

In the present study a simple method is described for obtaining 3D digital models of petroglyphs of different sizes and characteristics and its usefulness, in the study of this cultural heritage, is evaluated. For this research we used low-cost photogrammetric software and consumer-grade digital cameras, without any other surveying techniques. In order to test this methodology, three field research studies were carried out in Galicia (Spain).     

Assessment and Significance of a World War II battle site: recording the USS Emmons using a High‐Resolution DEM combining Multibeam Bathymetry and SfM Photogrammetry

The USS Emmons, a 106m US Navy Gleaves‐class destroyer minesweeper that sank in 40m of water off Okinawa Island, Japan after kamikaze attack in 1945, is used as a case study for examining the history, multivocal significance, and heritage management of a World War II naval battle site. A baseline record of the site was made using an innovative method incorporating precise control points obtained from high‐resolution multibeam echosounding bathymetry to generate 3D models using structure‐from‐motion photogrammetry. The 3D models produced can be used for sharing information about this underwater cultural heritage and for future in situ monitoring of the archaeological remains.     

3D model of the Can Sadurní cave

Graphic and metric information about the site and its environment and about the different structures and artefacts located are indispensable for the optimal management of an archaeological excavation. A Geographic Information System (GIS) proves useful in managing and analysing information and data obtained from different sources. Two techniques of data capture, Terrestrial Laser Scanning (TLS) and close range photogrammetry, are used to generate accurate and high-resolution 3D models of a cave, the silos and a combustion structure at the Can Sadurní site (Begues, NE Spain). This site is especially noteworthy on account of its complete stratigraphy of the Catalonian Holocene. The capture and processing of the photogrammetric and TLS data used to generate 3D models are discussed in detail. These models cannot be obtained by classic archaeological techniques since the record is made layer by layer, approximately one decimetre apart, with the result that the information between the layers is lost. Our findings highlight the potential of these techniques for obtaining accurate and photorealistic models that facilitate a complete analysis of the available information at an archaeological site.     

UAV and RPV systems for photogrammetric surveys in archaelogical areas: two tests in the Piedmont region (Italy)

Aerial photogrammetric surveys are usually expensive and the resolution of the acquired images is often limited. For this reason, different innovative systems have been developed and tested in order to perform a photogrammetric survey in an inexpensive way, with high-resolution images. In this context, one of the most promising acquisition techniques is represented by the use of Unmanned Aerial Vehicles (UAVs) equipped with a digital camera.     

Demonstration Survey of Prehistoric Reef‐Net Sites with Sidescan Sonar,near Becher Bay,British Columbia,Canada

Sidescan sonar was deployed in challenging shallow‐water conditions to demonstrate the potential for recording anchor‐stones left on the sea‐bed from prehistoric fishing operations. In less than three hours the survey successfully mapped a reef‐net site originally recorded in 1985 by diving archaeologists over many hours. In addition, 8 km of coastline were surveyed, resulting in the discovery and recording of one new underwater reef‐net site. Our understanding of evolving subsistence practices of the Straits Salish, for whom reef‐net fishing was a critical activity, may be enhanced by this survey method which provides cost‐effective access to data not otherwise being recorded. © 2011 The Authors