Church of the Holy Apostles

Aerial view of the Church of the Holy Apostles, Thessaloniki

CETI has published a short case study about their project to digitise the Church of the Holy Apostles in Thessaloniki. The fieldwork involved the terrestrial and aerial photography of the monument followed by a measured survey to capture key details.  A 3D model of the exterior of the monument was then produced using commercial Structure-from-Motion  and Dense Multi-View  3D reconstruction software.

A remote controlled GPS stabilized hexacopter used in the digitisation

Description of the monument

The Church of the Holy Apostles in Thessaloniki is situated in the square of the same name at the beginning of the modern Olympou Street. The church lies south of the decumanus (Saint Demetrius Street) around 50 meters from the west city wall and near the Litea Gate (which is ruined today).

Originally the church was the katholikon (main church) of a sizeable monastery. The dating of the church’s construction (along with its bell tower) is part of an ongoing scientific debate. The building is a four-column cross-in-square church. The nave is surrounded by two narthexes (porticos), a small rectilinear esonarthex and a U-shaped exonarthex. The designation of the church as Holy Apostles is of recent date and was said to be based on the existence of twelve vaults in the building. This popular association with the Apostles is documented in travelers’ accounts as early as 1735. The building is in a good state of preservation with much of its original construction elements intact and visible.

Fieldwork

The fieldwork was separated into three sessions. The first two involved the terrestrial and aerial photo shooting of the monument. For the terrestrial photo shooting session a pair of compact DSLR Samsung NX1000 at 20MP with a 20–50 mm lens along with tripods and monopods (3m-6m) have been used. On the other hand, for the aerial photo shooting session, a remote controlled GPS stabilized hexacopter has been used. The UAV was equipped again with the same type of digital camera and it was able to perform a 15 minutes flight per battery charge. The UAV was also capable of transmitting in real time the camera’s viewpoint to a ground station.

Hexacopter in use at the Church of the Holy Apostles

In addition, the orientation of the camera was performed by a different remote controller giving the team more flexibility during the aerial data collection phase. Six circular image sequences were captured at different heights starting from the terrestrial level at around 1.5 m. The total number of photographs that has been used for the generation of the 3D model of the monument was around 4,000. Finally, an empirical measurements session involved the measurement of short distances between several details on the surface of the monument. Again, a total of 10 distances between distinct points were captured in order to be used for the 3D data scaling and accuracy verification. During the digitisation phase, an undocumented inscription was discovered at the top of the monument and it is being currently being studied by the cultural heritage unit of the Athena research centre.

3D replica of the exterior of the Church of the Holy Aposles, Thessaloniki

3D replica of the exterior of the Church of the Holy Apostles, Thessaloniki

3D Model

Within the framework of the 3D-ICONS project, CETI has created a 3D digital replica of the monument’s exterior using a commercial Structure-from-Motion  and Dense Multi-View  3D reconstruction software. 

A high definition (1080p) video sequence of the monument’s 3D replica is available on YouTube