Application of a landscape feature classification technique to historical building facades

Abstract

Technological advances have led to the development of a range of non-destructive techniques for the assessment of stone decay. Of these evolving techniques, few are as extensively applied as 3D modelling for assessment of surface alteration. Many studies focus on alteration of elevation relative to a ‘baseline’ surface to determine the spatial distribution of surface change. These approaches are limited when dealing with historical stones, where through decay or architectural choices, original tool marks or base levels may not be apparent. However, these 3D scans of wall surfaces can be considered in much the same fashion as digital elevation models (DEMs) of landscape or earth surface features. Acceptance of this premise enables the application of comparative roughness assessments to determine the impact that different weathering pasts have had upon the microtopography. The study site for this work is Fitzroy Presbyterian Church in Belfast (UK). The church’s stonework was finished with a rough surface that obscures tool marks and through its ‘topographic’ complexity prevents the application of estimated geometric baselines. The church was built in stages and has been the subject of restoration campaigns, resulting in multiple wall sections of different ages and weathering histories. Two wall sections were scanned using the Konica Minolta VIVID 9i 3D scanner, creating models with submillimetre accuracy. The roughness assessment technique selected was topographic position index (TPI), a focal statistical technique developed to identify topographic features across landscapes. Using this technique, it’s possible to classify microtopographic features at a point on the wall surface.<br/