CI PA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
and difficult to record and represent in diagrams and 
models. 
- the walls, built of coral rag and covered with lime mortar, 
display highly eroded, undulating surfaces that pose a major 
challenge to automated and visual edge detection and line 
drawing. 
- the technical and economic limitations of an African 
environment render some of the methods and approaches 
applied elsewhere in documentation, impractical or entirely 
impossible. 
Figure 1. Views of the Western wall of the Gereza 
1.2 A brief historical account of Kilwa 
Kilwa Kisiwani was first settled around 800 AD and by 1320 it 
had grown into one of the most prominent trading centres of the 
East African Coast. Its splendid buildings include mosques, 
palaces and ordinary residential buildings. Kilwa supplied 
timber, ivory & other African products to Southern Arabia, the 
Persian Gulf and locations as far as India and China. Kilwa’s 
trade to the North reached Egypt and other Mediterranean 
countries. For quite some time, Kilwa also controlled the coast 
to the South as far as Sofala beyond the Zambezi mouth, a 
harbour from where gold mined in Zimbabwe was exported. 
Around the 15th Century, Kilwa faced growing competition 
from Mombassa and Malindi to its North and at the beginning 
of the 16th Century it was invaded and subdued by the 
Portuguese who built the Kilwa fortress in 1505 to signify their 
dominance over the island. When leaving the island after a short 
occupation the Portuguese reportedly razed most of the original 
fortress and in its “present form the fortress dates to the period 
of late Swahili revival and Omani expansion around 1800 AD”. 
First structures of the Great Mosque were built in the 11 th 
century and expanded significantly in subsequent centuries. 
Other than for some reconstruction in the 15 th century, the 
present mosque has retained its original form (Sutton 1998). 
After some economic revival in the late 18th Century, Kilwa 
faced a new period of occupation by Omani rulers based in 
Zanzibar at the beginning of the 19th Century. In 1840 the last 
Sultan of Kilwa was deported to Oman, thus ending the 
dominance of Kilwa. (Chittick 1974). 
2. DATA ACQUISITION 
Documentation data was acquired in three field campaigns, 
during which digital imagery, supported by control point 
surveys, was captured. A Cyrax 2500 laser scanner was 
available for the last field visit and experimentally employed as 
an additional documentation tool. 
2.1 Photography 
Digital imagery was captured using a Kodak DCS 330 camera 
with 14mm and 28mm lenses. The two camera-lens 
combinations were pre- and post-calibrated with the lens 
focusing ring firmly taped down. The repeatability of the 
camera-lens configurations after removal and re-attachment of 
the lenses were tested prior to the fieldwork. In a laboratory 
experiment both lenses were removed ten times each and the 
camera-lens system was recalibrated after each lens change. 
The interior orientation parameters proved consistent within the 
accuracy requirements of the planned documentation. The 
following requirements were considered in the design of the 
geometry of the camera stations and the camera orientations: 
Multi-image photography had to be acquired to provide 
optimal imagery for surface generation by multi-image- 
geometrically-constrained matching, the mathematical 
model employed in the in-house software employed for the 
project. 
Cameras had to be oriented with the image plane parallel to 
the principal surfaces (walls) to provide optimal data for the 
generation of ortho- images 
Oblique and rotated photography were required to 
strengthen the geometry of the photogrammetric 
triangulation 
Multiple diagonal photography was needed at both convex 
and concave building comers to provide links between 
surfaces in rectangular orientation. 
Photography from different elevations had to be captured to 
obtain texture and detail for the up- and down facing 
surfaces of ledges, windows and doors. 
Photographs were taken, with the camera handheld, from 
ground positions, elevated positions on the fortress structures 
and from a six-meter tall ladder. As the site is located between 
the equator and the Tropic of Capricorn, it was possible to 
photograph South- and North-facing walls in full sunlight by 
visiting the site in summer and winter. A total of approximately 
1000 photographs of the two structures was acquired, of which 
some 500 were finally used for the photogrammetric 
triangulation and the creation of the model. A number of 
marked control points, distributed over the structure, was 
surveyed using conventional survey methods. 
Figure 2. Entrance area of the Great Mosque