Conserving Africa's cultural heritage digitally

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					                                                                                                       Surveying
                                                                                                         technical
Conserving Africa’s
cultural heritage digitally
by Heinz Ruther, University of Cape Town


Many of Africa’s architectural heritage sites are in a poor condition and threatened by slow destruction through
environmental and human impact. Such deterioration often occurs hardly noticed, especially in countries
where poverty and other social and political problems dominate life and set other priorities.




E
        ven in the face of such adversities,   Database. It took some eight years          with the mission “to accelerate the
        the relevance of cultural heritage     of design, applications, exploration        adoption of productive and efficient uses
        for the interpretation of the          and negotiations in order to obtain         of information technology for the benefit
past, understanding of the present and         the necessary approvals and permits         of the worldwide scholarly community.”
forming of the future has been realized,       and, above all, the required financial      As one of its first projects, Ithaka
and African countries, with their rich and     support.                                    launched a new initiative to create an
widely unknown architectural heritage,                                                     online archive of international scholarly
                                               In 2004 a generous grant of the
are now responding with a number of                                                        resources, known as Aluka (the Zulu
                                               Andrew W. Mellon Foundation made the
initiatives. Many attempts have been                                                       word aluka means “to weave”, reflecting
                                               dream of the African Heritage database
made to record and preserve Africa’s                                                       Aluka’s mission of joining together in a
                                               possible, which then took the form of
tangible and intangible heritage.                                                          single place resources from around the
                                               a joint project of Ithaka/Aluka and the
                                                                                           world). The "African Cultural Heritage
Architectural structures, historical           University of Cape Town, with the author
                                                                                           and Landscapes Database" is one of
cities and landscapes are important            as the principal investigator. Ithaka
                                                                                           Aluka’s three clusters, with the other
components of heritage, and this has           was formed in 2002 with the support
                                                                                           two clusters collecting and making
given surveyors and geomaticians an            of the Mellon, Hewlett and Niarchos
                                                                                           available data on ‘Struggles for Freedom
opportunity to contribute their skills         Foundations as a non-profit organization,
                                                                                           in Southern Africa’ and ‘African Plants’
and expertise to the documentation
                                                                                              respectively. The database will be
and conservation of heritage.
                                                                                              linked to Mellon’s widely-used JSTOR
Originally this was done with tape                                                            database for scientific publications.
and theodolites, producing simple                                                             The African Heritage database is a
ground plans of buildings and                                                                 non-profit project and will be available
excavation sites, followed by the                                                             free of charge to the African scientific
addition of close range and aerial                                                            community, while for users outside
photogrammetry for the production                                                             Africa, the rules similar to those of
of 3D building models, ortho-images                                                           JSTOR will apply. The team from the
and maps of sites and cities. Now,                                                            University of Cape Town is responsible
the laser scanner has been added to                                                           for the creation of the spatial
the tool box of the documentation                                                             component of the database, and was
expert. Databases and GIS                                                                     involved jointly with Aluka staff in the
technology is used to manage,                                                                 design of the database.
analyse and represent the acquired
heritage data.                                                                               The African Cultural Heritage
                                                                                             and Landscapes Database
Over the past 30 years, the author
has had the opportunity to apply                                                              The principal objectives of the
all these technologies and tools                                                              African Cultural Heritage and
to the recording of archaeological                                                            Landscapes Database are the
and historical sites, such as the                                                             provision of spatial data for scholars
conventional survey of Dingaan’s                                                              and students as well as the creation
Kraal in Mgungundlovu, the                                                                    of a permanent record of historical
photogrammetric recording of                                                                  architectural structures and towns
the 3,6-million year old hominid                                                              in Africa in digital form for future
footprints in Laetoli and the laser                                                           generations. It will also serve as
scanning of the fortress in Lamu.                                                             a basis for their restoration and
Out of these experiences, combined                                                            reconstruction and the creation of
with a deep affection for the African                                                      awareness of cultural African heritage
                                               The Great Mosque of Djenne, Mali, and
continent, grew the idea of the African        below, a screen print of the model of the   within the international and the African
Cultural Heritage and Landscapes               Great Mosque.                               community through educational




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 SURVEYING                technical

     material. Local academics and                                                         of the structure and its immediate
     government officers are involved in                                                   surrounds, and provide quantitative
     the acquisition and processing of                                                     data on the structure, such as height
     the spatial data which will result in                                                 of pillars and walls, window widths
     the creation of capacity building in                                                  and wall thickness, all of which
     these areas. The database is also                                                     are relevant for architectural and
     expected to have an impact on                                                         historical research.
     cultural tourism.
                                                                                           The models are created by a
     The documentation and database                                                        combination of laser scanning and
     are based on state-of-the-art                                                         photogrammetry, with scanning
     methods from digital aerial and                                                       providing the bulk of the data, and
     close range photogrammetry,                                                           photogrammetry serving to fill in
     laser scanning, remote sensing                                                        obscured areas, or areas where
     and image processing, geographic                                                      a laser scanner cannot be set up.
     information systems (GIS) and CAD,                                                    Photogrammetric algorithms are also
     computer visualization, database                                                      employed to drape the photographic
     design, as well as conventional                                                       texture over the generated model
     surveying methods.                                                                    surface.
     It is important to note that the                                                      Both the laser scanner and digital
     spatial component of the database,                                                    photogrammetry produce point
     as produced by the UCT team, is                                                       clouds. This is done by direct
     only one aspect of the database, and                                                  measurement of direction and
     does not represent the full extent.                                                   distance in the case of the scanner,
     Equally important, or as historians                                                   and by multi-image matching
     might say, even more important,                                                       and bundle adjustment for
     is the attribute component of the                                                     photogrammetry. There is, however,
     database, which contains information                                                  no doubt that laser scanning will
     collected by a group of scholars                                                      play a prominent role in this area,
     and experts on African history. This                                                  without necessarily replacing
     information, consisting of historical                                                 photogrammetry entirely.
     documents, excavation reports,
     diaries of early travellers, old maps                                                 Once the point cloud has been
     and photographs, and scientific                                                       generated, a model is created by
     papers, is linked trough the database                                                 connecting the individual points to
                                                                                           form a 3D (as opposed 2.5D) tin
     to the spatial information of the
                                                                                           or similar surface. For the African
     GIS and the 3D models, with latter
                                                                                           Heritage Database, this is done with
     forming a visual focus for each of the   Mosque in Timbuktu, Mali, and below a
                                              screen print of the model of the mosque.   a variety of software applications,
     recorded sites.
                                                                                         ranging from those supplied with the
     The content of the database varies                                                  scanner, to open source and dedicated
     from site to site, depending on the                                                 commercial modelling applications. The
     complexity, extent and nature of the        models of the structure, showing        draping of the photographic texture
     site, but in principle will comprise        the outline, as well as all visible     over the model surface for the heritage
     mostly of the following for each site:      surface features.                       project is achieved through in-house
        Integrated spatial/geographical          2D line drawings and 3D CAD line-       software produced by the UCT team.
        information systems and databases.       models of the inside of structures,     The field work associated with laser
        Metrically accurate 2D ground and        based on conventional survey            scanning is relatively quick; for
        elevation plans of structures, as        techniques and/or photogrammetry.
                                                                                         example, it took the UCT team five
        well as maps of the immediate            Interactive 3D computer models,         days to produce the approximately
        vicinity of sites in GIS format.         visualisations and virtual reality      50 scans required to model the inside
        Metrically accurate 3D-CAD models        scenes.                                 and outside of the Great Mosque
        with artificial surface structure        Virtual historical and current          of Djenne, Mali. Registering the
        (medium resolution).                     landscapes of parts of cities and       various scans to form a single model,
        Metrically accurate 3D-CAD               landscapes based on rectified aerial    although often complex, can also be
        or virtual reality models, with          and satellite images.                   completed in relatively short time, but
        photographic texture ‘draped’ over       Extensive non-spatial data in digital   considerable time may be required
        the surface (medium resolution).         form (documents, photographs,           to fill the typically numerous and
        Detailed, metrically-accurate,           scientific papers, excavation           practically unavoidable gaps in the
        maximum resolution, 3D surface           reports, historical maps, etc.).        point clouds. Once again the Mosque
        models of selected sections of                                                   in Djenne can serve as an example.
                                              3D models
        structures with photographic                                                     The flat roof of the building contained
        texture ‘draped’ over the surface     Central to the spatial component of        close to hundred air inlets in the form
        (high resolution).                    the database are 3D computer models.       of low clay mounds, each equipped
        2D line drawings and 3D CAD - line    They serve to increase understanding       with an opening to allow an airflow



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 SURVEYING                technical

     into the building. It is obviously                                                             be dealt with, and administrative
     practically impossible to find a                                                               hurdles have to be overcome. But
     single position from where all sides                                                           for those involved in its execution,
     of each of these mounds can be                                                                 it holds exceptional rewards, the
     ‘seen’ by the scanner, and over
                                                                                                    chance to explore new technologies,
     a hundred positions would have
                                                                                                    visit sites of unique beauty and
     been required to guarantee full
                                                                                                    interest, and, above all, to be part
     coverage. In a case like this, it is
     necessary to fill gaps by manual or                                                            of the preservation of Africa’s past.
     semi-automated modelling, or, in                                                               Acknowledgements
     cases of larger ‘holes’ in the point
     cloud, by photogrammetry. This                                                                 The creation of the African Heritage
     problem can arise in a variety of                                                              Database would not be possible
     situations, and becomes a central          Untextured 3D model of Bet Jyorgis in Lalibela,     without the support of the Mellon
     factor in the processing and planning Ethiopia.                                              Foundation and the staff of Aluka,
     of architectural scans. In fairness                                                          especially Tom Nygren and Rahim
     to the new technology of laser                 Ghana, the fortress and town of Lamu          Rajan; the University of Cape Town;
     scanning, it must be noted, though,            in Kenya, the stele of Axum in Ethiopia,      the international expert group on
     that this problem is only of relevance         Great Zimbabwe in Zimbabwe, the
                                                                                                  African history and the expertise of
     in applications where every single             pyramids and temples of Meroe in
     surface characteristic and deviation                                                         the UCT Heritage Team members,
                                                    Sudan, and one of the walled cities of
     need be recorded. This is not generally                                                      Rudy Neeser, Christoph Held and
                                                    West Africa are planned for the next
     the case, but definitely of relevance for      two years.                                    Ralph Schroeder. The author gratefully
     erosion monitoring and conservation                                                          acknowledges their respective
     work in architectural applications. As         Conclusions                                   contributions to the project. He also
     a principle adopted for the African                                                          wishes to express his gratitude to
                                                    Heritage documentation, which was
     Heritage Database, every effort is made                                                      Geosystems Africa for the loan of the
                                                    once at the fringe of the surveying
     to model the surface as objectively as
                                                    and geomatics discipline, and, to             laser scanning equipment, as well as
     possible, with maximum accuracy and
                                                    those involved in it, more of a               Leica Geosystems, which, through
     a clear indication of areas which are
                                                    hobby than a professional activity,           their academic discount programme,
     manually generated, as opposed to
     being accurately surveyed.                     has become well established in                have made it possible to obtain
                                                    geomatics, with dedicated conferences         an HDS 3000 system at a greatly
     Not only buildings, but also landscapes        and symposia, working groups                  reduced rate.
     are modelled by draping medium                 in international bodies, and an
     or high resolution satellite images            international organization, CIPA. A           Contact Heinz Ruther,
     or digital aerial photography over             number of professional geomatics and          University of Cape Twon,
     DTMs of the area surrounding each              survey practices that are exclusively         Tel (021) 650-3573,
     site. This data type was included into         involved in heritage documentation,           heinz.ruther@eng.uct.ac.za
     the database in response to modern             have emerged worldwide, and an
     archaeological and historical thinking,        increasing number of documentation
     which sees sites not as isolated               projects are underway. Events such as
     features, but in the context of their          the recent destruction of the Bamiyan
     immediate and wider environment. 3D            Buddha statues in Afghanistan, and
     city models will be created for historical     the fortress of Bam in Iran, have
     cities such as Lamu and possibly               increased international awareness of
     others.                                        the need for accurate documentation,
     Site selection                                 and geomaticians and surveyors
                                                    have been recognised as the group
     In the first three-year phase of the           of experts best equipped for this
     project, ten to twelve sites have been,        task, provided that they work in
     or will be, documented. The majority           cooperation with heritage experts.
     of these have UNESCO world heritage
     site (WHS) status. The selection of            With very few exceptions, sites
     sites is based on the recommendation           in Sub-Saharan Africa were not
     of a group of experts on African history       part of the international spatial
     and decided in close cooperation with          documentation efforts. The African
     antiquities experts of the countries in        Cultural Heritage and Landscapes
     which the proposed sites are located.
                                                    Database project will hopefully fill
     The field work for the four WHSs,              this gap, create awareness of the
     namely Kilwa Kisiwani in Tanzania,             rich spectrum of African architectural
     Djenne and Timbuktu in Mali, as well           culture, and provide records for future
     as part of Lalibela in Ethiopia, has           generations. The project is technically
     been completed. Documentation of               complex and demanding. Logistical
     Elmina Castle and Ashante shrines in
                                                    and transport difficulties have to



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