Laser Technologies Document Historic Muslim Site in Cairo

by AScribe Newswire
April 25, 2007
The CyArk 3D Heritage Archive has archived 3D digital documentation of the Bab al-Barqiyya gate of the Ayyubid Wall, part of an extensive historic preservation and development project in Cairo of the Historic Cities Support Programme of the Aga Khan Trust for Culture (AKTC). The archived data and media consist of a High Definition Documentation (HDD) suite of data and media that include: 3D point cloud models, architectural CAD drawings, high resolution photographs, panoramic photographs and animations of this important historic example of Muslim architecture from the Ayyubid era.

The Bab al-Barqiyya (1176 CE) is a fortified gate that was built as a part of the Ayyubid wall by Salah al-Din after the fall of the Fatimid Dynasty. The wall was originally built to enclose and protect the existing Fatimid city in a single updated system that also included previously unprotected suburbs. Today the Ayyubid Wall defines the edge between the Darb al-Ahmar district of Cairo and the new al-Azhar Park. The Bab al-Barqiyya unites two parallel sections of the Ayyubid Wall at the place where they overlap. Interlocking the two walls, the volume of the gate serves both as tower for exterior defense and as a highly secure control space through which those entering had to execute somewhat disorienting turns and pass guards before entering the city. It is a unique and innovative design that attests to the ingenuity of the Syrian Ayyubid military engineers of the period. The ensuing years following the fall of the Ayyubid caliphate saw the Ayyubid Wall's gradual deterioration and eventual ruin until its recent restoration by the Historic Cities Support Programme of the Aga Khan Trust for Culture.

Today the restored historic Bab al-Barqiyya, has been the object of a study of the advantages of High Definition Documentation (HDD) which has been developed by CyArk to improve the speed, efficiency, and accuracy of archaeological and preservation documentation. CyArk is a nonprofit project of the Kacyra Family Foundation, a 501c.3 charitable trust, with the mission of "Preserving Cultural Heritage Sites through collecting, archiving and providing open access to data created by laser scanning, digital modeling, and other state-of-the-art technologies." HDD is CyArk's integrated documentation method that combines surveying, 3D laser scanning, and high definition photography processes that has proved to deliver a 60 percent time/cost savings over traditional archaeological documentation methods.

The technological core of HDD is high definition surveying (HDS) which utilizes a laser scanner to capture the physical features of a site and displays them in 3D as a "point cloud" model where each point represents the precise "x,y,z" location where the laser beam contacted the subject of study. The process becomes HDD when high resolution and dynamic range photography is integrated with the laser scanning, providing additional material and chromatic information for the 3D point cloud dataset, typically accurate to .5cm. These digital models can be used to generate a wide range of documents useful for historic preservation and heritage site management such as architectural drawings, condition assessment documents, and finite element method models for structural analysis. These are of great value to heritage site managers, archaeologists, and conservation professionals. But much visually rich HDD data can also be of great use for education and of interest to the general public. Such data from cultural heritage sites from around the world, including The Bab al-Barqiyya, can be viewed at the CyArk 3D Heritage Archive at www.cyark.org .

The Bab al-Barqiyya documentation was conducted in September 2006 at the beginning of Ramadan. The CyArk team included faculty from the Development of Integrated Procedures for Restoration of Monuments (DIAPReM) of the University of Ferrara. The scope of the project was to document the Bab al-Barqiyya gate itself, both exterior and interior, as well as twenty meters of wall to each side of the gate. The HDS 3D laser survey was executed with a Leica/Cyrax HDS 3000 by Alessandro Grieco and Daniel Blersch of DIAPReM. The 3D survey was coordinated and georeferenced to an average error of 2mm with an existing topographical survey conducted by survey engineers from the al-Ahzar Park staff. The final 3D laser scan survey produced master dataset point cloud model with a total of 43,175,477 points. High resolution and high dynamic range photography was executed from each of the laser scan set-up positions, by Oliver Monson who was Project Coordinator for CyArk.

The 3D documentation of the Bab al-Barqiyya is but a part of a much larger project funded by the Historic Cities Support Programme of the Aga Khan Trust for Culture (www.akdn.org/agency/aktc.html). AKTC is restoring the full 1.5 kilometer length of the Ayyubid Wall which includes fourteen towers. Two important monuments, the Khayrbek Mosque and the Aq Sunqur (Blue) Mosque sit newly restored by AKTC at the southern end of the wall. The Darb al-Ahmar district which adjoins the wall is a focus of historic preservation and community revitalization. Herein, not only are important monuments being restored, but AKTC is also funding the development of housing, education, medical and social services throughout the community. On the opposite side of the Ayyubid Wall, exists a 30 hectare park, created by AKTC, opened in 2005, where a vast refuse site previously existed. The new park landscape now provides much needed and appreciated first of its kind green public space for the citizens of Cairo. This introduction of open landscape and places of social gathering has been recognized internationally as a significant contribution to the quality of life to Cairo. Within this extensive project, CyArk's state-of-the-art HDD technologies and methods, bring significant innovations that are supporting this important work of historic preservation and community building in Cairo.
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