Digital Documentation of Greek Orthodox Church of Taxiarches in Ermioni


Digital Documentation of Greek Orthodox Church of Taxiarches in Ermioni

This paper presents the digital documentation of the Greek Orthodox church of Taxiarches (Taxiarchae) in Ermioni(Argolida, Greece) using Structure-from-Motion photogrammetry.

Taxiarchesis an earlyChristian church with later additions in the form of a pronaos (portico) and belltower, both dating from the 1930s. Recently, the foundations of a previously unknown ancient temple were revealed during repair works in the portico. This determined the scope of the survey programme, which focused on the digital documentation of the pronaos with particular attention to the floor and foundations of the much earlier temple. Moreover, a detailed survey of the load-bearing structure was required for the static evaluation of the building. Finally, a complete set of 2D architectural drawings was necessary for obtaining the necessary permits for conservation works.

The project requirements in terms of absolute accuracy were within 1-2cm, which was met by Structure-from-Motion photogrammetry as the chosen methodology. Initially, a control network was established extending both inside and outside the church. The network was measured by Total Station and referenced to the Greek National Grid (EGSA ’87) using RTK GPS. A number of targets (photogrammetric control points), placed in both interior and exterior horizontal and vertical surfaces, were subsequently measured from the control stations.

The church exterior was photographed using a UAV-mounted digital camera SONY NEXSN 16MP with 16mm lens. Aerial images were captured at nadir orientation while flying in a criss-crossing pattern, as well as several oblique images at varying heights followed by ground-based photography. The same camera was used in the interiors of main church and pronaos from various heights and using additional lighting systems to improve internal lighting conditions.

The images were processed in Pix4D with good results in terms of absolute accuracy. The software was used to produce point clouds and 3D mesh models, which were then merged using CloudCompare. A high-resolution orthophotomosaic of the pronaos floor and excavated temple foundations was also produced using Pix4D. Finally, the 3D point cloud was used as a basis for the production of a complete set of 2D CAD drawings of the church, which were required both for a structural evaluation and legal permits for further repair works.

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