Zamani Team Surveys House of Wonders After Collapse

House of Wonders Documented by Zamani Team

On the 25th of December 2020, the front of the iconic House of Wonders (Beit-al-Ajaib) in Stone Town, Zanzibar, partially collapsed resulting in the tragic loss of life and the destruction of its North-West corner. The building was under restoration after an earlier collapse. 

The building is a central component of the UNESCO World Heritage site “Stone Town of Zanzibar” which was inscribed in the UNESCO World Heritage List in 2000. The building was completed during Sultan Bhargash’s rule in 1883 and acquired its name because it was electrified and equipped with the first lift in East Africa. The three-storey building has a footprint of 50 by 50 m, was 37m and is now 29m high. The, collapsed tower was a later addition constructed to replace the nearby lighthouse after it was destroyed in 1896 during the Anglo-Zanzibar war. This war is known as the shortest war in history with a duration of some 40 minutes. 

As part of a UNESCO emergency response, the Zamani Team from the University of Cape Town, executed the first of three technical missions from the 29^th January to the 3rd of February. The missions were designed to assess the extent of the damage to the House of Wonders, propose measures to stabilise the building and advance measures towards its rehabilitation. The Zamani teams was called upon to generate a highly accurate 3D model of the remaining building by means of a laser scanning/photogrammetry survey. Accuracy of the data and speed of execution were key in this project, as the availability of data was crucial for the immediate stabilisation and the planning of subsequent rehabilitation of the House of Wonders.

It was most fortuitous that a full laser scan/photogrammetry survey of the House of Wonders had been carried outby the Zamani team  in August 2019.

2019 and 2021 Scanning Campaigns

Zamani’s 2019 scanning mission had two objectives, the creation of a virtual 3D model of the House of Wonders for the re-enactment of historical scenes for a TV documentary on the “Omani Presence in East Africa” and to add a new site to the Zamani Heritage Database (www.zamaniproject.org). 

• The objective of the scanning mission in 2021 differed from all previous projects carried out by the Zamani team. Typically, a documentation project aims at the acquisition of spatial data as a record for the future, for research and education, for the development of tourism, as a site management tool, and it can serve in the planning of restoration interventions. While the latter was a common objective for 2019 and 2021, the 2021 mission had the important additional aim to detect and quantify any major deformations in the remaining structure by comparing the 2019 and 2021 models. Besides using the obvious tool of “cloud comparison“ for this analysis, the models were explored with a number of other methods, partly adapted from traditional geomatics based deformation analysis techniques. The results of this comparison can only be published at a later stage, as the investigation of the collapse is still ongoing.

2019 3D model (left) and 2021 3D model (right)

Equipment and Survey

In 2021 it was vital to capture the essential data in a short period of time due to the volatile nature of the site. Laser scanning formed the foundation of the field campaign supported by extensive  photography and GNSS measurements. The use of a tablet, connected to the Z+F scanner via Wi-Fi, made it possible to register the laser scans on site and thus economise the data acquisition process. Terrestrial and aerial photographs, aligned to the colour laser scans using Reality Capture software, served to provide additional texture  and coverage in the areas that could not be reached by the laser scanner. The aerial photography was acquired by manually navigating the drone over and around the building. The model was georeferenced via GNSS. In 2021 the drone was especially relevant in the collapsed areas of the building where physical access was impossible or too dangerous. Beside a textured 3D model of the House of Wonders, a panorama tour was created based on 150 panoramas taken by the laser scanner in 2019 for further visual comparisons and for the planning of any reconstruction. 

The table below shows the equipment used by Zamani in Zanzibar in 2019 and 2021. 

Zamani pilot doing pre-flight checks on the DJI Phantom 4 Pro drone

Further documentation on Zanzibar

The tragic collapse of the House of Wonders confirms, in the strongest possible terms, the importance of spatial documentation of heritage sites. In the interest of the protection of Zanzibar’s heritage the Zamani project plans to continue its work in Stone Town, which began in 2007, with the documentation of two Persian Baths, followed by the Peace Memorial, Palace Museum, the Stone Town Waterfront, the Old Fort the Forodhani Garden and the nearby Mtoni Palace.

It is planned to revisit some of the earlier monuments and document additional buildings in the Old Town of Zanzibar. The image below shows a combined colour point cloud of the Stone Town Waterfront, the House of Wonders and the Old Fort.

Combined colour point cloud of the Waterfront of Stone Town, including the House of Wonders and the Old Fort.

For the further monitoring of possible movements of the House of Wonders, the Zamani team plans to install a permanent GNSS monitoring system on the rooftop of the building as well as to monitor the surrounding area by a network of GNSS points established during the 2021 mission. 

The team wishes to express appreciation for the support provided by the Minister of Tourism and Culture, the Stone Town Conservation & Development Authority, UNESCO and the Saville Foundation. 

Cape Town 24^th March2021

Heinz Ruther

Roshan Bhurtha 

Bruce McDonald 

Ralph Schroder