Refinement of retrospective photogrammetry: an approach to 3D modeling of archaeological sites using archival data

Photogrammetric 3D modeling of archaeological excavations, structures and monuments using archival photographs has achieved encouraging results thus far. This paper discusses the limitations posed by analogue archival photographs in photogrammetric processes and limiting the photographs used to one moment in time as well as photogrammetric methods with regard to camera calibrations by eliminating elements that reduce the quality of the modeling. This can be particularly important for models using archival photographs from different cameras and photographic times. When archival photographs are made available in an online database, there have been a number of processing elements that contribute to a reduction in the quality and accuracy of the photographs and their ability to be used viably in 3D modeling. Based primarily on retrospective photogrammetric projects undertaken in 2018, this paper demonstrates how archival photographs can perform at a level equivalent to contemporary digital photographs which have metadata. The work presented here illustrates the use of photographs archived by American School of Classical Studies in Athens for reconstructing archaeological sites in the Athenian Agora in order to aid in ascertaining deterioration as well as determining means of preservation and restoration.