ABSTRACT

The visual comparison of 2D images, or ‘photographic monitoring’, is commonly used in cultural heritage conservation to assess rates of deterioration and the impact of interventions. While it is an accessible technique, three-dimensional changes can be difficult to discern and identifying change can be subjective. Structure from Motion (SfM) photogrammetry, which generates 3D point clouds from digital photographs, has the potential to make monitoring more objective and more informative by recording three dimensions of change rather than two. A methodology was tested on the Romanesque wall paintings of St Botolph’s church, Hardham, UK to develop a SfM photogrammetric condition monitoring system that is affordable, portable, non-contact, and repeatable. Commercially available camera equipment was used for capture, and readily available or free software was used to generate and detect change between two 3D point clouds. Time-SIFT, an in-software workflow of point cloud alignment, was used as a reliable non-contact method to replace adhered or embedded registration points on the wall to align the clouds from different capture epochs. The technique was able to identify change in the wall paintings, with the smallest verified changes at a scale of 0.5 mm. The results are discussed in relation to their advantages over 2D imaging, the avenues for further research, and the limitations of applying the technique on site. This research demonstrates the potential of photogrammetry as an accessible in situ condition monitoring tool using a workflow and equipment tailored to working on sites with wall paintings.

摘要

2D 图像的视觉比较或“摄影监测”通常用于文化遗产保护，以评估恶化率和干预措施的影响。虽然它是一种可访问的技术，但很难辨别三维变化，并且识别变化可能是主观的。运动结构 (SfM) 摄影测量，从数码照片生成 3D 点云，通过记录三个维度而不是两个维度的变化，有可能使监测更加客观和提供更多信息。在英国哈德姆的 St Botolph 教堂的罗马式壁画上测试了一种方法，以开发一种经济实惠、便携、非接触且可重复的 SfM 摄影测量状态监测系统。使用市售的相机设备进行拍摄，并且使用现成的或免费的软件来生成和检测两个 3D 点云之间的变化。Time-SIFT 是一种软件内点云对齐工作流程，它被用作一种可靠的非接触式方法来替换墙上的粘附或嵌入配准点，以对齐来自不同捕获时期的云。该技术能够识别壁画中的变化，最小的验证变化为 0.5 毫米。讨论了这些结果相对于 2D 成像的优势、进一步研究的途径以及在现场应用该技术的局限性。这项研究证明了摄影测量作为一种可访问的潜力 被用作一种可靠的非接触方法来替换墙上的粘附或嵌入配准点，以对齐来自不同捕获时期的云。该技术能够识别壁画中的变化，最小的验证变化为 0.5 毫米。讨论了这些结果相对于 2D 成像的优势、进一步研究的途径以及在现场应用该技术的局限性。这项研究证明了摄影测量作为一种可访问的潜力 被用作一种可靠的非接触方法来替换墙上的粘附或嵌入配准点，以对齐来自不同捕获时期的云。该技术能够识别壁画中的变化，最小的验证变化为 0.5 毫米。讨论了这些结果相对于 2D 成像的优势、进一步研究的途径以及在现场应用该技术的局限性。这项研究证明了摄影测量作为一种可访问的潜力 进一步研究的途径，以及在现场应用该技术的局限性。这项研究证明了摄影测量作为一种可访问的潜力 进一步研究的途径，以及在现场应用该技术的局限性。这项研究证明了摄影测量作为一种可访问的潜力现场状态监测工具，使用专为在有壁画的现场工作而设计的工作流程和设备。