Proceedings 18 th International Symposium CIPA 2001 
Potsdam (Germany), September 18 - 21, 2001 
PHOTOGRAMMETRIC RECONSTRUCTION AND 3D VISUALISATION 
OF BET GIORGIS, A ROCK-HEWN CHURCH IN ETHIOPIA 
Thomas Buehrer & Zhang Li & Armin Gruen 
Institute of Geodesy & Photogrammetry, ETH Zurich, Switzerland 
E-mail: buehrer@geod.baug.ethz.ch & zhangl@geod.baug.ethz.ch & agruen@geod.baug.ethz.ch 
Clive Fraser 
Dept, of Geomatics, University of Melbourne, Australia 
E-mail: c.fraser@eng.unimelb.edu.au 
Heinz Ruther 
Dept, of Geomatics, University of Cape Town, South Africa 
E-mail: heinz.ruther@eng.uct.ac.za 
KEY WORDS: Heritage Recording, Lalibela Rock Churches, Photogrammetric Reconstruction, Visually Realistic Model, Texture 
Mapping, Ethiopia 
ABSTRACT 
Around 1200 AD, a number of remarkable rock churches were constructed in Lalibela, a town in northern Ethiopia. One construction 
manner stands apart in its uniqueness. This is the rock-hewn monolithic church, which while imitating a built-up structure is actually 
cut in one piece from the rock and separated from it by an all-around trench. The best known of the monolithic churches is Bet 
Giorgis (St George’s Church), a UNESCO World Heritage site. The narrowness of the trench around the church makes the 
photogrammetric image recording demanding. Numerous photographs were necessary for a sufficient coverage. In a first phase of the 
3D model generation only monoscopic image measurement was carried out. First results were not satisfactory due to problems in 
properly defining homologous points in the respective images. Such an ancient building suffers from erosion damages and hence 
lacks sharp comers and edges. Additional helpful construction features such as parallelism, perpendicularity and planarity can barely 
be exploited as the building is relatively irregular. For these reasons additional measurements are performed in stereo 
photogrammetric mode. Still, there is a high demand of visual interpretation and manual measurements are absolutely necessary for 
producing a comprehensive 3D model. For the 3D model rendering, the ETH-developed visualisation software Disp3D, which 
employs a view-dependent texture mapping procedure, has been used. The project, which is ongoing, will ultimately result in the 
production of a fine-detail visually realistic digital model of the church and its immediate surroundings. 
1. THE ROCK CHURCHES OF LALIBELA 
The town of Lalibela lies in the province of Wollo in northern Ethiopia, some 640 km from Addis Ababa. Lalibela is internationally 
renowned for its rock-hewn churches. Their creation is ascribed to King Lalibela, one of the last kings of the Zagwe dynasty. All 12 
churches in the town are thought to have been constructed within a 100-year period around 1200 AD. Of the three basic types of 
rock-churches in Ethiopia, built-up cave churches, rock-hewn cave churches and rock-hewn monolithic churches, the last, which is of 
current interest, is unique to the Lalibela region. Arguably the most significant of Lalibela’s four strictly monolithic rock-hewn 
churches is Bet Giorgis (the Church of Saint George), which is regarded as being the most elegant and refined in its architecture and 
stonemasonary. Fig. 1 shows the 12 x 12 x 13m Bet Giorgis standing within its 25m square trench. 
Fig. 1: Bet Giorgis rock-hewn church, Lalibela Fig. 2: Ornaments at upper windows and weathered 
comers of cornices in the foreground