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ibul 2004 
DIGITAL STEREO-ORTHOPHOTOS OF ARCHAEOLOGICAL SITES FROM SMALL FORMAT AERIAL 
PHOTOGRAPHS 
M. Jáuregui *', L. Jáuregui ", L. Chacón *, J. Vílchez 
? Photogrammetry Institute, Engineerring Faculty, Universidad de Los Andes, Av Tulio Febres, Mérida 5101 — (manuel, 
iluis, leirac, vilchez)@ula.ve 
Commission V, WG V/4 
KEY WORDS: Photogrammetry, archaeology, restitution, orthoimage, DTEM, pixel 
ABSTRACT: 
The digital orthophoto is a valuable tool for representing an object on orthogonal projection at a known scale, due to the relation between 
its relatively low production cost and the photographic detail representation in its true position. When this orthophoto is accompanied by 
its mate image, named stereomate, its advantages raises significantly, because the observation can be performed in 3D. 
Along the production process of the digital orthophoto the mate image can be produced with a minimum of additional processing. From 
the DEM, the parallaxes for each image point, and the pixel position for each point of the mate image are computed in a reference 
coordinate system. Finally a resampling is performed on the mate image in order to complete the image from a visual point of view. That’ 
is why we thought to use the stereo-orthophoto to facilitate the study of an archaeological site by archaeologists because the same allows, 
not only the observation, but also the annotation of thematic observations resulting from field surveys. (directly in orthogonal position 
when done on the orthophoto) 
The practical example on this paper has been done in the old mission town of San Antonio de Mucufio, which was founded in 1620 and 
abandoned in the early ninety century. The only way to obtain the images over the town, was using small format aerial photographs 
(SFAP), taken from a small airplane. The SFAP is a reliable tool to interpret archaeological sites 
1. INTRODUCTION 
In aerial photogrammetry commonly it has been used the 230 x 
230 mm. photograph, as standard format for the taking of aerial 
photographs. In a parallel way, the film formats of 35 mm and 70 
mm, known as Small format Aerial Photography (SFAP) also 
have been used. Nevertheless, these small formats have not been 
widely accepted for photogrammetric surveys due to the non 
metric characteristics of those cameras. Its main application has 
been in the field of photointerpretation. 
At present, the digital methods have permitted the determination 
of the external and internal orientation parameters of the camera in 
a simple form, expanding the potential of use of the SFAP in 
photogrammetric surveys in zones of small extension, when 
comply the following conditions: i) The area is it sufficiently 
small so that photogrammetric survey using standard format, are 
hot competitive economically. ii) The area is sufficiently large so 
that a topographical survey is not competitive economically. 
This paper shows a procedure used for the generation of digital 
stereo-orthophoto from SFAP in an archaeological site of difficult 
access, where is not possible to take standard format photographs 
lo an appropriately scale. This work is part of a cartographic 
documentation project of this site. 
The digital stereo-orthophoto consists of an orthophoto and an 
associate image or stereomate containing the corresponding 
parallaxes in order to achieve the stereoscopic vision. The 
orthophoto and stereomate are produced in digital form. The 
digital orthophoto is generated from the geometric information of 
the Digital Terrain Elevation Model (DTEM) of the area, and of 
the radiometric information of the original image, applying the 
colinearity equations and resampling procedures to the radiometric 
values of the original image. The digital stereomate is generated 
adding the parallaxes to the points image in the digital orthophoto. 
These parallaxes are calculated from the heights resulting from 
intersection of the DTEM with the plane of reference, assuming an 
appropriate relation between photographic base and point height 
(B/H). The stereo-images are useful in the representation of the 
planimetric information of the area, and in the photointerpretation 
of the zone. 
2. PROCEDURE 
The procedure scheme used for the generation of the stereo- 
orthophoto is shown in the figure 1. Each stage of the procedure 
is explained briefly in the next sections.