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.