Digital Documentation of Reflective Objects: A Cross-Polarised Photogrammetry Workflow for Complex Materials

Abstract The quality of digital documentation of cultural heritage sites and objects is influenced significantly by the complexity of the subject. Complexity is an encompassing concept comprised of a range of factors including material properties and surface characteristics. Highly reflective items pose a challenge to traditional workflows, which has been previously addressed with a range of mitigating techniques and strategies, often including cross-polarised photogrammetry lighting setups to omit specular type reflections. However, in the removal of reflections to achieve more robust surface geometry, important information about the specular albedo of the surface can be lost. In this paper we demonstrate an accessible single camera cross-polarised photogrammetry workflow to retain the diffuse and specular albedo information. The results have enabled qualitative assessments about the individual objects and their materials through the workflow. The items discussed include ceramic, metal and wood material types, and through the separation of specular information offer unique improvements to their visualisation and insights to their physical condition for conservation purposes.