Traditional and Modern Methods of Surveying Architectural Heritage: ... the Fortified Island of Malta 
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analysing local situations in different detail; 
representing building volumes more accurately, producing cross sections; 
obtaining useful information for the preservation of the environment; 
enabling all kinds of future data processing and integration without negatively affecting the metric quality; 
providing an accurate georeferenced base for GIS. 
The extensive amount of information contained within this 3-Dimensional product can be further integrated with terrestrial 
topographic or photogrammetric surveys (e.g. façades) into a single reference frame for a complete representation of the urban 
system and its monuments. It is also possible to use these surveys for the preparation of new representation techniques (e.g. metric 
virtual reality products). 
Compared to smaller scale aerial surveys, a similar undertaking presents significant technical difficulties, particularly: 
high costs and long production time; 
difficulties in recognising the various objects, and subsequently their interpretation; 
the need for a strong integration between photogrammetry and terrestrial surveys; 
the complexity of statistical quality control, due to the large amount of information. 
For this reason, rigorous technical specifications, which define the various phases of the mapping process, were prepared. This also 
included provisions for the graphical representation of the surveys as well as the definition of the different layers, related primarily to 
the different elements forming the structure of the fortifications. Both from a historical and typological aspect, this, in particular, 
necessitated an extensive input from experts in military architecture. 
The accuracy required for the planimetric co-ordinates of a point is ± 20 cm while that for the Z of a well-defined altitude point is ± 
10 cm. Aerial photographs were taken at an average scale of 1:3100. This was mostly conditioned by the flight altitude limits 
imposed by the Civil Aviation Department of Malta, especially since the flights were affected over the most densely populated 
regions of the Island (Valletta-Floriana, Mdina, Gozo). 
The figures shown below represent an example of part of an aerial photograph of the medieval city of Mdina, situated on a 
promontory in the centre of the Island, and the corresponding restituted plan (fig. 3). 
Figure 3: Detail of an aerial photograph of the South-eastern part of the historic city of Mdina, 
and the corresponding restituted plan 
2.2 Close Range Photogrammetry 
A number of close-range photogrammetric techniques were adopted for the documentation of architectural elements. The methods 
used were decided upon after the building characteristics, the scope, and desired precision of the surveys had been evaluated. Metric 
and semi-metric, small and medium format cameras were used, while the restitution was carried out using both analytical and digital 
instrumentation. Digital rectification was primarily used in the case of objects prevalently on one plane. Extensive experiments on the 
use of digital orthophotos and automatic surface modelling, using matching methods implemented on medium-level DPWs, were also 
carried out. 
Figure 4 shows the restitution of Zabbar Gate (Cottonera Lines, Vittoriosa). Three distinct representational methods, vectorial 
treatment of the structural elements, detailed representation of the principal architectural elements, and a rectified raster image 
representation of the central parts were used. Different representations were plotted on distinct layers structured on various levels of 
information required for the eventual restoration of the gate, and specifically designed to be referenced to a database. The vector 
restitution was carried out using an analytical stereoplotter (Digicart 40).