ORTHOIMAGE PROCESSING IN ARCHEOLOGY.
THE SITE OF COLONIA CLUNIA SULPICIA
(PENALBA DE CASTRO, BURGOS - SPAIN)
G. Gillani a , M, Roggero b
a Departamento de Prehistoria y Arqueología, Universidad de Valladolid (España)
gillani@atlantic.polito.it
b Dept, of Georesource and Territory, Politecnico di Torino, C.so Duca Degli Abruzzi 24, 10129 Torino, IT
roggero@atlantic.polito.it
KEY WORDS: Archaeology, Digital image processing, Orthoimage, Reconstruction, Archaeological Heritage Conservation,
Cultural Landscapes Conservation, Photographic Recording and Documentation, Detection.
ABSTRACT:
In preserving and recovering cultural and archeological heritage, aerial photography and remote sensing, are useful tools, not only
for the detection of new sites, but also for archeological documentation and investigation. Multi-source and multi-temporal imagery
materials can guarantee a continuous monitoring of the state of site conservation.
We have studied some image processing techniques, with reference to archeological applications, achieving two goals: obtaining
more readable and measurable images. This methodology is very different from the traditional use of aerial photography in
archeology: not only stereo-photo-interpretation of the site, but digital filtering to magnify archeological evidence.
We have applied this experimental methodology to some sites in Spain. In this paper we present the results on the site of a Roman
town in the Iberian peninsula, Colonia Clunia Sulpicia (Penalba de Castro, Burgos). For some years, we have collected some
information about urban texture without excavating, using nadiral and oblique photography. The main product of this research is the
digital orthophotography of the entire site, that is very useful for archeologists.
3D exploration of digital orthophotography, makes the perception of micro-reliefs and slope irregularities in the site possible. The
identification of alterations in micro-reliefs, provides the elements to identify layers of material from the ancient roman town and to
highlight the urban texture and the access to the town.
Digital orthophotography is useful also for the reconstruction in virtual reality of the town, inserting the reconstructed models of the
best known buildings.
1. HISTORICAL BACKGROUND
Colonia Clunia Sulpicia, capital of Conventus Cluniensis in the
Province of Tarraconensis in Hispania, was the largest Roman
city in the Iberian Peninsula.
Situated on a limestone plain at an altitude of 1000 m it reached
an extension of 130 hectares. It was founded ex-novo in the
Augustean/Tiberian epoch as a sinecism of two pre-existent
celtic-iberian settlements the celtic-iberian nucleus of Clunioq
(which gave its name to the Roman city) and the settlement
known as Arauzo de Torre. The city underwent a remarkable
economic development during the 1st and 2nd centuries A.D.
and various archaeological expeditions have brought to light the
forum, the basilica, roman baths, an abattoir and other blocks
occupied by private houses as well as the theatre which exploits
natural features of the terrain and has been a popular subject for
prints since the 19th century.
We have been dealing with the problems of urban topography
for some years now to try to solve two problems. The first is to
try to understand if the entire area of 130 hectares was a single
built-up area or if the urban layout took the form of separate
city quarters. The second question regards some problems of
urban orientation since, from the digs, we have discovered three
different orientations.
With these problems in mind, years ago we decided to analyse
the site using particular methods. The strategy adopted
consisted of using photographs to reconstruct a 1:1000 scale
model of the area, with details of the plateau on a scale of 1:
500. This model also contains details of buried archaeological
evidence identified from aerial photographs. The data thus
acquired are integrated with those obtained from a study of the
excavated areas and from further studies of structures which,
although buried, are visible on the terrain The product obtained
is a digital relief model of all the data useful for an urbanistic
analysis of the city.
The following step in the development of the methodology
consists of improving the acquisition of the information present
in the aerial photographs and in the Digital Terrain Model
(DTM) of the hill on which the city is built. We decided to
move in two directions which will be illustrated in the
following pages.
First of all starting with the available data we created a digital
orthoimage of the entire area of the hill using the DTM as a
base and orthoprojecting onto it the photograms in scale 1:
12000 used for making the model. The purpose was to use the
digital orthoimage obtained for evaluating micro-reliefs on the
site, altimetry differences and other anomalies which might be
useful in identifying means of access to the city, possible piles
of rubble resulting from the ruins of ancient roman buildings
etc.
Secondly, we decided to test some specific filters for image
enhancing. In the present work we use a vertical photograph on
scale 1: 4000, which represents a sector situated between the
Casa de Taracena and Termas de Los Arcos. The purpose of
enhancing the image is to discriminate between archaeological
and non-archaeological traces, which are so numerous in aerial
photos.