COMPARISON OF 3D REALITY CAPTURE TECHNOLOGIES FOR THE SURVEY OF STONE WALLS

The maintenance of the external fabric of historic buildings constitutes a large portion of overall building life cycle costs. Advanced reality capture and data processing technologies have the potential to transform existing survey practice, providing surveyors with objective data pertaining to building fabric, in a more rapid (frequent), safe and cost-effective manner. In this paper, we present a unique evaluation of several Terrestrial Laser Scanning (TLS) and photogrammetric (PG) systems that assess their relative strengths for the survey of stone walls. The assessment is conducted using an historic building selected for its representativeness of form, fabric and condition. The work considers performance in terms of data accuracy and precision, data completeness, and process efficiency. The results show that, while TLS provides good geometric data to generate accurate and valuable 3D models, the quality of PG reconstructions can be also be sufficient in such contexts. And considering the relatively low-cost and portability of modern digital cameras compared to laser scanners, photogrammetry can constitute a realistic alternative to TLS. In addition, mounting a camera on a UAV could further solve access issues, preventing the need for any additional infrastructure (e.g. scaffolding), which would be required when employing TLS. However, a lesson drawn from this work is that effective acquisition of photogrammetric data requires careful planning to select the appropriate camera settings and picture density (and locations) to ensure accurate and reliable photogrammetric reconstruction. This process may be referred to as: Planning for Photogrammetry (P4P).