3D digital survey of the Bab al-Barqiyya Gate at al-Ahzar Park in Cairo (Egypt) and acquisition of HDR photographic data

The 3D digital survey with HDS 3000 laser scanner of the Bab al-Barqiyya Gate has been worked out during the field work in September 2006, as a collaboration project between the DIAPReM research centre and Consorzio Ferrara Ricerche (CFR) for Kacyra Family Foundation (KFF) in direct relation with Aga Khan Trust for Culture (AKTC).

The object to survey has been divided in different areas. The scanner positions and the target point distribution could be set up in a way that permitted the registration of all scans without the necessity of an external support. Therefore the scan data itself resulted in already in a closed network, which makes possible a major control during scan registration. The 3D digital survey was integrated by a topographical survey, conduced by staff members of the al-Ahzar Park, in which nearly all targets have been acquired (not all areas were accessible with the total station).
The acquired data has been registered in two partial models: one with the “room” scans, one with the “site” scans and a further complete model with an average error in the target point constraints of about 2mm. A registration of the complete model (room & site) with the topographic model was done, in order to obtain a reference to former surveys and to connect indirectly with other monuments in the area by using the georeferenced overall network of the site.
After a series of efforts and reducing to just three targets of constraints belonging to scans from different scanner positions, it was possible to process a georeferenced registration with an average error of 2mm.