Terrestrial Laser Scanning and Digital Photogrammetry as Tools for the Archaeological Recording – The Case of Convento de Cristo (original) (raw)

Abstract

The “Convento de Cristo”, located in the city of Tomar, represents the best that has been produced in the history of Portuguese architecture. This monumental site, built between the 12th and 17th century, includes a Templar castle and a convent of the Order of Christ, and is classified as World Heritage by UNESCO since 1983. In this paper we intend to discuss the potential and usability of the methods and tools of digital photogrammetry and terrestrial laser scanning (TLS) to the recording and production of base documentation as support to heritage interventions. A set of documentary case studies accomplished in this monumental site will be presented. In these case studies documentation for stratigraphical analysis prior to Rehabilitation and Restoration planning design, was produced regarding the knowledge of the historical and cultural evolution of the site. The archaeological recording was done at the level of deposits and walls. In the same context, documentation as support to Conservation interventions was also produced. The following approaches were used: i) rectified photography as a low-cost and very practical method, ii) automatic three dimensional reconstruction from multiple images with the state-of-the-art structure-from-motion (SFM) software VSFM (Visual SFM), followed by a dense reconstruction with the multi-view-stereo software CMVS+PMVS, in a approach that minimized the processing time, maintaining quality of output, iii) TLS as a tool for geometric and radiometric survey, iv) image interpretation and processing of TLS reflectance images as a tool for the differentiation of materials and constructive systems and assessment of the conservation state. Three dimensional data enabled spatial comparison between the phases of excavation. The complimentary potential between the techniques of TLS and automatic photogrammetry was demonstrated by using low altitude aerial images (taken with helium balloon with remotely controlled digital camera) allowing a more comprehensive documentation, in particular in those situations where TLS presents limitations (higher parts of buildings). Interpretation and processing of TLS reflectance images was demonstrated to be a valid tool for the inquiry of the architectural object that allows one to extract relevant information both for Archaeology and Conservation. It was possible to distinguish between several types of joints (even to perceive early interventions done with cement mortars), to detect several constructive patterns through the analysis of the stone cuts, to calculate a vegetation index, and to differentiate between organic and inorganic materials.

Key takeaways

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  1. Digital photogrammetry and terrestrial laser scanning (TLS) enhance archaeological recording and heritage documentation.
  2. Case studies reveal TLS and automatic photogrammetry effectively support stratigraphical analysis prior to restoration.
  3. ADP allows rapid creation of dense point clouds, improving efficiency in archaeological documentation.
  4. TLS reflectance images reveal construction features and conservation states that traditional methods may overlook.
  5. The integration of these technologies requires digital literacy for effective data management and analysis.

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