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DEVELOPMENT OF AN INTEGRATED SYSTEM OF TRUE ORTHO-RECTIFICATION. 
THE ALTAIS LRTO SYSTEM 
R. Antequera d , P. Andrinal 3 , R. González 3 , S. Breit a , J. Delgado b , J. L. Pérez b , M. Ureña b , S. Molina 6 
d Altáis, S.L. altais@altais-sl.com 
b Grupo de Investigación Sistemas Fotogramétrico y Topométricos. Universidad de Jaén, jdelgado@ujaen.es 
KEY WORDS: Most Right Method, True Orthophoto, Light Orthophoto, Nadiral Profiles Method, Multi-Visibility Analisis 
Method. 
ABSTRACT: 
At present orthophotographs are essential sources of information in all areas. The generation of these products in urban areas can be 
difficult and specific rectification methods are neededin order to obtain advanced orthoimages that usually have been denominated 
as true orthophoto. In this paper, the principal results of a research project (DATOS -Development of an Advanced True Orthoimage 
System for urban information source, sponsored by PROFIT Program from the Spanish Ministry of Industry, Tourism and Comerce) 
are presented. This system is developed thanks to the collaboration of a private company Altáis S.L. and the University of Jaén, 
using data from the company HIFSA for the different phases of the work. In this contribution, the different phases for the 
development of the system and the obtained basic results are presented. 
1. INTRODUCTION 
Since the beginning of digital orthorectification methods in the 
90s there have been important changes in cartography that have 
brought orthophoto to the most demanding cartographic product 
thanks to the simplicity on their generation methods (less time 
consuming methods and less production cost) and also for the 
countless applications as graphical base for geographical 
information systems. Nevertheless, the classic methodology of 
digital orthophoto generation presents some difficulties 
especially when the surface registered in the imagery to be 
orthorectify includes areas with high altitude changes. 
These problems are specially important where relief is 
particularly complex due to the existence of buildings, that are 
areas of high interest as they concentrate most of the economic 
activities that imply important (and fast) changes that must be 
registered within cartographic information in a reasonable 
period of time. 
In order to resolve this problem different production strategies 
have been developed to compensate these limitations: geometric 
flight desing (increase of longitudinal and transversal 
overlapping areas, selection of the optimal direction of flight, 
restriction of time windows within appropriate dates in order to 
avoid shadow presence, selection of cameras with less FOV, 
etc.) and making an effort to improve the quality of imagery 
using less rigorous solutions with low possibility to automate 
them (alterations of DTM to improve the visual aspect of the 
imagery, patch of imagery to avoid stretching, occluding and 
deformed areas, image enhancement methods to extract detailed 
information, etc.). All these strategies imply the increment of 
production costs and also the limitation on its applications, 
especially in urban areas. A perfect knowledge of the digital 
surface model (DSM) means a perfect correction of aerial 
photography, however, actual orthorectification methods do not 
resolve efficiently element rectification problems, occluding 
areas, mosaiking of images and shadows. This way, the 
commercial methods developed for digital orthophoto 
generation seem to resign the quality reached with these 
cartographic products, assuming limitations of techniques and 
reasoning deficiency in the geometric nature of aerial 
photography and the quality of altimetry data. 
2. ORTHOPHOTOS TODAY 
The most extended concept of orthophoto is based in correction 
of aerial imagery to terrain level, obviating rectification of all 
elements, artificial or natural, existing within it. 
This is, certainly, a simplified concept of the problem to correct 
aerial imagery, and it resolves most of the problems raised in 
agro-environmental projects: Parcel and Agricultural GIS 
establishment, inventories (Citric, Vineyard, etc.), Identification 
of Registered Properties, Control of Aid Requests for 
Herbaceous Crop Terrain and Fodder Terrain, Land Use and 
Cadastral Mapping, etc. This kind of orthophoto, named as 
Ground Ortho (GO), is yet very useful in urban areas, however 
it presents some problems when dealing with urban planning 
projects, because in these areas many occlusions due to 
existence of leaning objects in the terrain force in many 
occasions to do additional field work to complete the work and 
not letting to do a direct analysis and interpretation with 
imagery. 
Apart from the occlusions due to leaning objects, there is 
another phenomenon that obstructs the exploitation of imagery 
directly: shadows, which makes the quality of work worst and 
also it conditions the dates to obtain imagery, restringing the 
time of the year to flight when the sun leaning is higher, and 
reducing the daily window capture. 
Finally, it is true that the quality of Ground Ortho in rural areas 
is good, but it also presents the described problems, which 
makes difficult the extraction of measurements directly from the 
orthophotography in elements not rectified: viaducts, bridges, 
etc. Also, it’s typical to see deformations and stretching areas 
within these imagery and zones with high slope: costs, cliffs, 
etc. that could be avoided considering shots with appropriate 
perspectives. 
Nowadays, there is True-Ortho (TO) generation systems, but 
they present the following disadvantages: